Median Handbook

Median Handbook
Interim Version

The purpose of this document is to guide
the professional through the existing rules,
standards and procedures, as well as to
provide current national guidance on the
best ways to plan for medians and median
openings.

Unless stated otherwise or specifically
referenced, this is not a set of standards
or a Departmental Procedure but is a
comprehensive guide to allow the
professional to make the best decisions on
median planning.

The primary thrust of this handbook is
the unsignalized median opening. Even
though much of this material can be used
with signalized intersection planning, ,
issues of signalized queues and signal
timing are not covered in detail.

Florida Department of Transportation
State of Florida
Systems Planning Office
605 Suwannee St.
Tallahassee, Florida 32399
www.dot.state.fl.us/planning

MEDIAN HANDBOOK

FDOT Median Handbook 2 Interim Version 2/9/2006

MEDIAN HANDBOOK

PURPOSE

Median Handbook
PURPOSE

Purpose The purpose of this document is to guide the professional
through the existing rules, standards and procedures, as well
To provide guidance on as to provide current national guidance on the best ways to
designing and placing median plan for medians and median openings.
and median openings. Unless stated otherwise or specifically referenced, this is not
a set of standards or a Departmental Procedure but is
a comprehensive guide to allow the professional to make the
best decisions on driveway planning.
The primary thrust of this handbook is the
unsignalized median opening. Even though much of this
material can be used with signalized intersection planning, ,
issues of signalized queues and signal timing are not covered
in detail.

Please direct questions
and concerns to:
Gary Sokolow
gary.sokolow@dot.state.fl.us
850-414-4912


MEDIAN HANDBOOK

Acknowledgements In addition to all the Team members, we would like to recognize the
lifelong work of Dr. Vergil Stover for the impact his work has had on
this document.
The material we used to create this document came from many of the
important access management documents written over the last 40
years. Specifically though, we borrowed heavily from the following
documents. These documents should be used for further illumination
of the guidance in this handbook
Access Management Manual (Kristine Williams and Vergil Stover)
– Transportation Research Board – Center for Urban Transportation
Research
Transportation and Land Development (Vergil Stover) –
Institute of Transportation Engineers

Handbook Contributors: Theo Petrisch
Joel Leisch
Vergil Stover, Center for Urban
Transportation Research

Authors/Editors: Gary Sokolow, Central Office
Vergil Stover, Center for Urban Transportation Research
Frank Broen, Teach America

Statewide Access Antonio Acosta, D-6 Tom Hancock, CO Marshall Sander, D-2
Gary P. Amig, D-1 Tony Hailey, D-1 Rory Santana, D-6
Management Group: Rafael deArazoza, D-6 Dan Igelesias, D-6 Jim Scott, D-2
Ingrid Birenbaum, Tpk Charley Locke, D-3 Judith A. Smith, D-7
Carlos Bonilla, CO Armando Lopez, D-6 Deborah Snyder, D-1
Felix Blanco, D-6 David Lynch, D-2 Ronald Steiner, D-6
David Burlison, VMS George Marek, D-5 Greer Stephens, D-3
Donald Cashdollar, D-1 Robert May, Turnpike Michael Tako
June Coates, D-3 Alex Meitin, D-6 Janak S. Thakkar, D-4
Beth M. Coe, D-4 Jim Mills, CO Clark Turberville, D-4
Robert Downie, CO Delfin Molins, D-6 Freddie Vargas
Tom Dyal, D-2 Priscilla D. Moore, D-2 Jack West, D-5
Gary Ewin, D-1 Vicente Noboa, D-4 Jim Wood, D-5
Fred Ferrel, D-5 David W. Olson, D-7 Timothy Whitley, D-2
Ronald Fetzko, D-5 Jonathan Overton, D-4 Donald Witmer, D-1
Terry Fleischner, D-5 Robert Pearce, D-2 Carol Wright, D-2
Jorgr Frases, D-6 Ed Petersen, D-5
Carleen Flynn, Turnpike Ray Pippitt, D-4
Al Gilbronson, D-7 Alan G. Rothmann, D-4
Javier Gonzalez, D-6 Tony Russo, D-1
Ed Gassman, D-3
John Grant, CO

District 1 = D-1, etc.
Central Office = CO


MEDIAN HANDBOOK

PURPOSE ....................................................................................................................................3
PURPOSE ....................................................................................................................................3
Purpose .................................................................................................................................3
Acknowledgements ...............................................................................................................4
Handbook Contributors:.........................................................................................................4
Authors/Editors: .....................................................................................................................4
Statewide Access Management Group: ................................................................................4
Introduction ...................................................................................................................................9
INTRODUCTION ..........................................................................................................................9
1.1 Medians and their Importance for safety ........................................................................9
Why do we use medians? .....................................................................................................9
What are the Benefits of Medians? .....................................................................................10
How Do Medians Fit in with Access Management?.............................................................10
1.2 11
MEDIAN OPENINGS DEFINED — WHAT IS THE FUNCTION OF A MEDIAN OPENING?
.............................................................................................................................................11
1.3 13
CRASH COMPARISON AND PUBLIC OPINION OF ROADS WITH AND WITHOUT
MEDIANS ............................................................................................................................13
1.3.4.....................................................................................................................................15
DEPARTMENT POLICY ON MEDIANS AND MEDIAN OPENINGS ..................................15
Rule 14-97...........................................................................................................................15
Multi-lane Facility Median Policy .........................................................................................17
Plans Preparation Manual ...................................................................................................17
What is the impact of these Standards? ..............................................................................18
Median Opening Decision Process .....................................................................................18
FDOT Procedure: ................................................................................................................18
625-010-020 ........................................................................................................................18
District Median Opening Review Teams..............................................................................18
Guiding Principles................................................................................................................19
Minimum Queue Storage Requirements .............................................................................19
Conditions for More Flexibility .............................................................................................20
Other Considerations...........................................................................................................20
Conditions for Less Flexibility or Greater Scrutiny...............................................................21
Unfavorable Conditions .......................................................................................................21
Retrofit from Center Turn Lanes to Restrictive Median .......................................................21
Other Department Criteria and Standards ...........................................................................21
IMPORTANT CONCEPTS..........................................................................................................23
IMPORTANT CONCEPTS IN UNDERSTANDING MEDIANS AND MEDIAN OPENING
PLACEMENT ..............................................................................................................................23
2.1 23
IMPORTANCE OF ROADWAY FUNCTIONAL CLASSIFICATION.....................................23
Hierarchal Priority of Median Openings ...............................................................................25
2.2 26
MEDIAN OPENING PLACEMENT PRINCIPLES................................................................26
Median Opening Placement Principles................................................................................26
AVOID MEDIAN OPENING FAILURE.................................................................................28
2.3 PARTS OF THE FUNCTIONAL AREA OF AN INTERSECTION ..................................29
Perception Reaction Time/Distance ....................................................................................29
Right Turn Weave Distance.................................................................................................29


MEDIAN HANDBOOK
(Right Turn Weave Offset)...................................................................................................29
Full Width Median................................................................................................................31
Deceleration and Length of the Left-Turn Lane ...................................................................32
Total Deceleration Distance (Includes Taper) .....................................................................32
Florida DOT Standard Index #301.......................................................................................32
2. 4 Design Speed/Entry Speed ..........................................................................................33
Entry Speed .........................................................................................................................34
Non-Peak Hour Speeds.......................................................................................................35
Queue Storage ....................................................................................................................35
Rule of Thumb: ....................................................................................................................37
Queue Length Adjustments for Trucks ................................................................................38
Median Opening Spacing — How All These Factors Impact the Spacing of Openings ......38
2.4 40
WHAT DISTANCE IS NEEDED FROM A FREEWAY RAMP TERMINAL TO THE FIRST
MEDIAN OPENING? ...........................................................................................................40
2.5 43
MEDIAN END TREATMENTS.............................................................................................43
A Strictly Bullet Nose Opening ............................................................................................43
2.5 44
MEDIAN OPENING LEFT TURN RADIUS..........................................................................44
2.6 45
MEDIAN OPENING LENGTH .............................................................................................45
Excessively Wide Median Opening .....................................................................................45
2.7 46
PAVEMENT MARKINGS AND SIGNING ............................................................................46
Sight Distance.............................................................................................................................47
SIGHT DISTANCE AS IT RELATES TO MEDIANS AND MEDIAN OPENING DESIGN ...........47
3.1 47
INTRODUCTION TO SIGHT DISTANCE CONCEPTS .......................................................47
AREA SIZE OF VEHICLE ...................................................................................................48
TIME OF VISIBILITY ...........................................................................................................48
WHAT IS STOPPING SIGHT DISTANCE? .........................................................................48
3.2 49
SIGHT DISTANCE FOR SPECIFIC MEDIAN OPENING MANEUVERS ............................49
Turning left through a Median as a Two-Step Maneuver.....................................................50
Sight Distance for U-Turns ..................................................................................................51
Sight Distance for Left Turn into Side Street .......................................................................51
Left Turn Lane Offset...........................................................................................................51
From Plans Preparation Manual ..........................................................................................52
3.3 54
LANDSCAPING AND SIGHT DISTANCE ISSUES .............................................................54
Major Criteria for Decisions on Sight Distance and Planting Area and Spacing in Medians54
Median Width ..............................................................................................................................59
MEDIAN WIDTH .........................................................................................................................59
4.1 59
Function Determines Median Width ....................................................................................59
4.2 60
ANATOMY OF MEDIAN WIDTH .........................................................................................60
4.3 60
Minimum and Recommended Widths..................................................................................60
4.4 61
SOME EXAMPLES..............................................................................................................61


MEDIAN HANDBOOK
4.5 62
MINIMUM TRAFFIC SEPARATOR WIDTH AT INTERSECTIONS.....................................62
4.6 62
PEDESTRIAN CONSIDERATIONS AT TRAFFIC SEPARATORS .....................................62
4.7 62
SEEING TRAFFIC SEPARATORS AT INTERSECTIONS..................................................62
4.8 62
MINIMUM MEDIAN WIDTH FOR U-TURNS .......................................................................62
4.9 63
DESIGN FOR TRUCKS ......................................................................................................63
Special U-Turn Considerations ...................................................................................................65
SPECIAL U-TURN CONSIDERATIONS.....................................................................................65
5.1 65
AASHTO GUIDANCE ON WIDTH AND U-TURNS .............................................................65
5.2 66
OPTIONS FOR U-TURNS...................................................................................................66
1. Wide medians..................................................................................................................66
2. Median “Bulb-Out” ...........................................................................................................66
3. Flare-Out (Jug Handles) ..................................................................................................67
Two Examples of a Flare.....................................................................................................67
5.3 69
TRUCK U-TURNS ...............................................................................................................69
Alternatives for accommodating u-turns by large vehicles (such as delivery, trucks and
semis) ..................................................................................................................................69
5.4 70
U-TURN LOCATIONS .........................................................................................................70
U-Turn at Signalized Intersections ......................................................................................70
U-Turns in Advance of a Signal ...........................................................................................72
U-Turn After Signal ..............................................................................................................73
5.5 75
PLACEMENT IN RELATION TO DRIVEWAYS...................................................................75


MEDIAN HANDBOOK


MEDIAN HANDBOOK

Introduction
1

INTRODUCTION
1.1 Medians and
their
Importance for Why do we use medians?
safety

Vehicular Safety — to prevent crashes caused by head-on and
crossover traffic, headlight glare and
traffic turning left.

Pedestrian Safety — to provide a refuge for pedestrians
crossing the highway.

Vehicular Efficiency — to remove turning traffic from through
lanes thereby maintaining highway
operating speed.


MEDIAN HANDBOOK

Restrictive medians and well designed median openings are
known to be some of the most important features in a safe and
efficient highway system. The design and placement of these
medians and openings is an integral part of the Access
Management practice.

What are the
• Safety
Benefits of
• Fewer/less sever accidents
Medians? • Less auto/pedestrian conflict
• Efficiency
• Higher levels of service
• Less stop and go traffic
• Aesthetics
• More room for landscaping and pedestrians
• More attractive corridors
• Less asphalt

Restrictive medians help in both low and high traffic situations,
but where traffic is high, the benefits are greater.
Properly implemented median management will result in
improvements to traffic operations, minimize adverse
environmental impacts, and increase highway safety. As traffic
flow is improved, delay is reduced as are vehicle emissions. In
addition, roadway capacity and fuel economy are increased, and
most importantly, accidents are less numerous and/or less severe.

How Do Medians Fit in Access Management is the
with Access location, spacing and design of:
Management?
Driveways
Medians
Median Openings

Signals

Interchanges


MEDIAN HANDBOOK

1.2
MEDIAN OPENINGS • Median openings provide for cross traffic movement.
DEFINED — WHAT IS
THE FUNCTION OF A • Median openings allow left turns and u-turns from the
MEDIAN OPENING? highway.

A typical median opening that allows all turns has 18 major
conflict point

One way to limit the number of conflicts is through the design of
median openings. This is a “directional” median opening serving
a side street, a design which greatly reduces the conflict points by
limiting the number of allowed turning movements.

By providing a restrictive median along arterial roads, we can
assure that the number of conflict points is kept to the minimum.
Through use of restrictive medians, almost every driveway along
the corridor essentially becomes a right-in and right-out driveway
with only two conflict points.


MEDIAN HANDBOOK

The location of
median openings To assure efficient traffic operation full median openings should
has a direct only be at locations which are thoughtfully placed along the
relationship to highway. If median locations are properly spaced when
signalized, traffic can be progressed at efficient and uniform
highway efficiency
operating speeds.
and traffic
progression

For More Information on Signal Spacing and Progression:
• NCHRP Report # 348 - Access Management Guidelines for
Activity Centers (Section 7-3)
• V.G. Stover, P.B. Demosthenes and E.M. Weesner,
"Signalized Intersection Spacing: An Element of Access
Management," Compendium of Papers, 61st Annual Meeting
of the Institute of Transportation Engineers, September 1991.


MEDIAN HANDBOOK
CRASH COMPARISON AND PUBLIC OPINION OF
1.3 ROADS WITH AND WITHOUT MEDIANS
Research has shown that restrictive medians are
a large safety benefit. In 1993, an evaluation of
urban multilane highways in Florida revealed
that the crash rate, where there are restrictive
medians is 25% lower than those with center
turn lanes.

Some in the field complained that comparing
Memorial Drive the restrictive median roadways with those
Data
• 4.3 Miles roadways with center turn lanes was an unfair
• 6 Lanes comparison because they felt that the center
• 40,000 to 48,000 Vehicles per Day
• Speed Limit 45 MPH turn lane facilities were in areas with a high
Before percent of left turns, and that most crashes are
• Two way left turn Lane
After caused by left turns. In the early 1990’s
• Raised Median (14 ft width) Georgia DOT sponsored, “before and after”
• 14 Median Openings Provided
• 7 public streets were not given median
research on a Memorial Drive, a particularly
openings hazardous section of roadway in the Atlanta
• U turns allowed at all openings but one area (DeKalb County).
Memorial Drive Crash The research clearly showed that not only did
Findings mid-block crash rates go down, as expected,
but intersection crashes decreased significantly.
Forcing more left turn traffic through a few
Mid-Block Crashes Intersection Crashes
openings was expected to increase the crash
rate, but hopefully decrease the severity. But
the opposite proved to be true.
- 24%
- 55%

Center Turn Lane The researchers in the Georgia study felt that
Driver Perspective the decrease in intersection crashes, even
though traffic volumes increased at
Stop
intersections, was that the “Driver Information
Left Left
Load” was decreased by having well placed
and visible median openings. These increase
Left driver expectancy as shown in the exhibits
Merge Merge

Focus Areas - 3
Source: Sear Approach Directions - 6
Brown Group and NYDOT


MEDIAN HANDBOOK

Median - Driver Perspective

Stop

Merge

Focus Areas - 2
Approach Directions - 2
Source: Sear Brown Group and NYDOT

Other research has shown that the presence of
Access & Pedestrian Safety
restrictive medians makes the environment
Atlanta, Phoenix, Los Angeles
safer for pedestrians.
Pedestrian-Vehicle Crash Rates by Median Type

Intersection 0.97 Non-Traversable
2.49
(1) TWLTL
2.32
Undivided
Mid-Block 3.86
6.66
(2) 6.69

0 2 4 6 8
Pedestrian Crash Rates for Suburban Arterials
(1) Crashes per 100 million entering vehicles
(2) Crashes per 100 million vehicle miles
SOURCE: Bowman and Vecellio, 1994.

When medians are constructed, they can be
designed with the pedestrian in mind. Here’s
an example from Colorado where a pedestrian
cross over was made part of the design to more
easily allow neighborhood walkers to cross this
multilane roadway.


MEDIAN HANDBOOK

1.3.4
DEPARTMENT POLICY
ON MEDIANS AND
MEDIAN OPENINGS

Rule 14-97 Administrative Rule Chapter 14-97 establishes the seven
classifications for state highways and the criteria and procedures
for assigning these classifications to specific roads. These
classifications contain separation standards for access features.
Essentially, the Department of Transportation determines which
roads are the most critical to providing high speed, high volume
traffic, and these end up with the highest of standards.
Medians and median openings are regulated through the
requirement for a restrictive median in certain classes. For those
classes, spacings between median openings are regulated. The
Median Opening Spacing Standards and how these are measured
are found in the following Figures.
Access Management Standards
From Rule 14-97
Class Medians Median Openings Signal Connection

Full Directional More 45 MPH
than 45 and less
MPH Posted
Posted Speed
Speed
2 Restrictive 2,640 1,320 2,640 1,320 660
w/Service Roads
3 Restrictive 2,640 1,320 2,640 660 440
4 Non-Restrictive 2,640 660 440
5 Restrictive 2,640 660 2,640 440 245
at greater at greater
than 45 MPH than 45 MPH
Posted Posted
Speed Speed
1,320 1,320
at at
45 MPH or 45 MPH or
less Posted less Posted
Speed Speed
6 Non-Restrictive 1,320 440 245
7 Both Median 660 330 1,320 125 125
Types


MEDIAN HANDBOOK


MEDIAN HANDBOOK

Multi-lane Facility
Median Policy 2.2.2 Multilane Facility Median Policy
Plans Preparation All multilane facilities shall be designed with a raised or
Manual restrictive median except four-lane sections with design speeds of
40 mph or less.

Facilities having design speeds of 40 mph or less are to include
sections of raised or restrictive median for enhancing vehicular
and pedestrian safety, improving traffic efficiency, and attainment
of the standards of the Access Management Classification of that
highway system.

Topic #625-000-007 January 1, 2006
Plans Preparation Manual,
Volume I - English Design Geometrics and Criteria 2-18

Since 1993, the Multi-lane Facility Policy essentially directs all
Department multilane projects over 40 mph in design speed to
have a restrictive median.
It also directs our designers to find ways to use restrictive
medians in all multi-lane projects, even those below the 40 mph
design speed.
An example of a small pedestrian refuge that could be used on a
5-lane section is shown in the following Figure.


MEDIAN HANDBOOK

What is the impact of One of the impacts of these standards is the concentration of more
these Standards? left turn and more U-Turns. These are things that need to be
handled by careful planning and design. In response to this, the
Department created the Median Opening Decision Process.

WHAT IS THE IMPACT
OF THESE
STANDARDS?

HOW DO WE DEAL
WITH THE
CONCENTRATION OF
LEFT AND U-TURNS?

Median Opening Meeting the median opening spacing standards of Rule 14-97 can,
Decision Process at times, pose a practical problem. Therefore the Department
FDOT Procedure: created a process to analyze deviation from the standards found in
625-010-020 the rule. The process allows Project Managers a 10% deviation
from the standards for full median openings and gives complete
flexibility to Project Managers on decisions involving directional
median openings as long as they meet minimum traffic
engineering standards for storage, deceleration, sight distance and
maneuverability. All deviations greater than this must go to a
district Median Opening Review Team for further study and
recommendation.
MINOR DEVIATIONS (MEDIAN OPENING SPACING)

District Median Each District has a Median Opening Review Team to consider
Opening Review Teams deviations from Rule 14-97 standards but, safety, traffic
efficiency and functional integrity of the highway system must be
taken into account.


MEDIAN HANDBOOK

Guiding Principles
The decisions of the District Median Opening should be made
with the following principles of the process:

Safety of the entire transportation system
(not just the State system)

Traffic Efficiency

Functional Integrity

Minimum Queue • A critical measure for good median opening design is left
Storage Requirements turn queue storage.
• Site or project specific projections of queue storage should
be use at all major or critical intersections. (Due to the
variable nature of left turn demand, actual turn volumes
should be reviewed in many cases. Designs should also be
conservative enough to handle some of the uncertainty in
demand.)

Where left turn volume is unknown and expected to be minor
• Urban/suburban minimum = 4 cars or 100 ft.
• Rural/small town minimum = 2 cars or 50 ft.

Sources:
• Plans Preparation Manual Vol. I - 2.13.2 Queue
Length for Unsignalized Intersections
• Median Opening Decision Process (FDOT) Topic
No.: 625-010-020
RECOMMENDED QUEUES


MEDIAN HANDBOOK

Conditions for More The process also gives guidance for where more flexibility (or
Flexibility less) should be considered. Conditions that may be viewed
favorably in evaluating a proposed median opening deviation
include:
• Opportunities to alleviate significant traffic congestion at
existing or planned signalized intersections
• Opportunities to accommodate a joint access serving two
or more traffic generators
• Existence of un-relocatable control points such as bridges,
waterways, parks, historic or archaeological areas,
cemeteries, and unique natural features
• Where strict application of the median opening standards
in 14- 97.003(1) Figure 2, would result in a safety,
maneuvering, or traffic operational problem
• Where directional opening would replace existing full
service median opening.

Source: Median Opening Decision Process (FDOT)

Other Considerations • Un-relocatable or unique historic features
• Where strict adherence would cause safety problem
• Where a directional would replace a “full” opening
• Emergency vehicle openings


MEDIAN HANDBOOK
Conditions for Less • The Strategic Intermodal System (SIS) and the Florida
Flexibility or Greater Intrastate Highway System (FIHS)
Scrutiny • Facilities Access Class 2 or 3
• Full median openings and signal spacings
• Median openings in a high accident corridor or location,
unless a safety benefit can be clearly shown
• Situations where circulation can be provided through other
alternatives

Unfavorable Conditions

• Where any unsignalized intersection would be unsafe
(such as close to the Interchange at SR 436 and I-4 in
Altamonte Springs)
• Openings in functional area of intersection
• High crash locations
• Where alternatives exist

Source: Median Opening Decision Process (FDOT)

Retrofit from Center
Turn Lanes to Existing 5 lane sections on the FIHS and those facilities over
Restrictive Median 28,000 in daily traffic should be given the highest priority for
retrofit.

All 7 lane sections should be given a high priority for retrofit.

Other Department Other Department documents containing important standards and
Criteria and Standards criteria for medians and median opening design are:
• Plans Preparation Manual
• Standard Index
• Florida Highway Landscape Guide


MEDIAN HANDBOOK


MEDIAN HANDBOOK

IMPORTANT CONCEPTS 2

IMPORTANT CONCEPTS IN UNDERSTANDING MEDIANS
AND MEDIAN OPENING PLACEMENT

2.1
IMPORTANCE OF
Highway functional classification means classifying highways
ROADWAY
with respect to the amount of access or movement they are to
FUNCTIONAL
provide and then designing and managing each facility to perform
CLASSIFICATION that function.
“The failure to recognize and accommodate by suitable
design each of the different trip stages of the movement
hierarchy is a prominent cause of highway
obsolescence.” AASHTO Green Book (Chapter 1)
There is no definite dividing line between each of the classes or
rigid rules defining what makes a street a local, collector, or
arterial. The three basic functional classes represent a continuum
of facilities that range from unrestricted access (no through
traffic) to complete access control (no local traffic).
An important access management principle is that roads should
not connect directly to another of a much higher classification.
For instance, a local road may be connected to a major collector,
and a major collector may be connected to a minor arterial, but a
local road should not connect directly with a major arterial. See
the following Figure for illustration of this principle.


MEDIAN HANDBOOK

Full median openings serve a “Major” transition function. This
means that on arterial roads they should only be provided at
arterial junctures of the road system as defined for the public
street or internal circulation systems.

ROADWAY FUNCTION CLASSIFICATION

“Openings should only be provided for street
intersections or for major developed areas”
(AASHTO Green Book)
In keeping with the principles of functional design adopted by the
AASHTO Green Book, the choice of which opening is to be
closed in order to resolve the inadequate length of another
requires that the hierarchy (importance) of the median openings
be established. The following is a suggested hierarchy of median
openings.


MEDIAN HANDBOOK

Hierarchal Priority of
Median Openings
Priority of 1A and 1B are 1A Arterial intersection of freeway ramp
the same. 1B Major arterial-to-major arterial

2 Other signalized intersections (public street or private access
connection) which conform to the signalized intersection
spacing standard
3 Other intersections on major arterials which conform to the
signalized intersection spacing standard but which are not as
yet signalized
4 Signalized intersections (public street or private access
connection) which do not conform to the signalized
intersection standard
5 U-turn or left-turn/u-turn opening serving 2 or more public
and/or private connections. If two such conflicting openings
each serve 2 or more connections, the one with the higher
volume would typically be given the higher priority . If the
volumes are similar, the median opening serving the larger
public street volume would be given the higher priority.
Other U-turn/left-turn ingress should normally be given priority
over left turns out egress because ingress capacity is higher and
produces less conflict than the left turn out movement.
Source: Adapted from the course material notes of Virgil Stover.

For More Information on Roadway Hierarchy:
• AASHTO Green Book, Chapter 1.
• Transportation and Land Development, Stover/ Koepke


MEDIAN HANDBOOK

2.2
MEDIAN OPENING
PLACEMENT
PRINCIPLES

The basic concept used in median opening location and
design is avoidance of unnecessary conflicts which result
in crashes.
The unsignalized median opening is essentially an intersection.
Properly designed it will have an auxiliary lane allowing the left
turning vehicles to decelerate without interfering with the through
movements of the leftmost through lane.
Important: The through lane is where the fastest traffic is.
This means that the potential of high speed crashes is the greatest
there. Before any design of this area can be done, it is important
to know what speed, maneuvering distances, and storage
requirements you should design for.
Median Opening
Placement Principles
• Follow the spacing criteria in Rule 14-97 as close as
possible.
• Median openings should not encroach on the
functional area of another median opening or
intersection.

“Driveways should not be situated within the functional
boundary of at-grade intersections. This boundary would
include the longitudinal limits of auxiliary lanes.”
AASHTO Green Book


MEDIAN HANDBOOK

Median Openings That Allow Traffic Across Left- Turn
Lanes Should Not Be Allowed
A median opening within the physical length of a left-turn bay as
illustrated in the Figure is potentially dangerous. Such an opening
violates driver expectancy.

Median openings that allow the following movements should
be avoided
across exclusive right turn lanes
across regularly forming queues from neighboring
intersections
Avoid openings across right turn lanes due to the danger of
queues building up across the opening area. The problem here is
that when these queues build, “Good Samaritans” might allow the
left turner through only to crash with a vehicle moving freely in
the separate right turn lane.


MEDIAN HANDBOOK

Exclusive right-turn lanes are most appropriate under the
following conditions:
1. No median openings interfere,
2. The right-turn lane does not continue
across intersections, and
3. No closely spaced high volume driveways.

AVOID MEDIAN Median opening failure can occur when critical features of the
OPENING FAILURE functional area of the opening are not designed appropriately.
This is usually due to the inadequate space for left turn storage.
This can either result in excessive deceleration in the through
lane, because cars are stored in the needed deceleration length of
the functional area. Or, if it is critically under-designed it can lead
to cars “hanging out” in the through lane for an even more
hazardous situation.
WHAT IS MEDIAN OPENING FAILURE?

THROUGH LANE QUEUE BLOCKS ENTRY INTO THE
LEFT-TURN LANE

Watch out for this
problem
When the queue in the through traffic lane spills past the left-turn
bay, turning vehicles are trapped in the queue, as illustrated in this
figure. The left-turning vehicles are not able to move into the turn
bay until the queue advances. Dual left turn lanes may be more
prone to this problem.


MEDIAN HANDBOOK

2.3 PARTS OF THE The functional area consists of distance traveled during
FUNCTIONAL AREA OF perception reaction time, plus deceleration distance, plus queue
AN INTERSECTION storage.
Perception Reaction The perception-reaction time required by the driver varies. For
Time/Distance motorists who frequently use the street this may be as little as one
second or less. However, unfamiliar drivers may not be in the
proper lane to execute the desired maneuver and may require
three or more seconds.
.
Suggested Perception/Reaction distance may be used as follows:

Suggested Perception and Reaction Distance

Area Seconds 35 MPH 45 MPH 55 MPH
Rural 2.5 130 ft 165 ft 200 ft
Suburban 2.0 100 ft 130 ft 160 ft
Urban 1.5 75 ft 100 ft 120 ft
For More Information On Perception-Reaction Time: AASHTO Green Book

Right Turn Weave Vehicles turning right from a downstream driveway will need
Distance distance to weave if they are turning left at the next opening
(Right Turn Weave Offset)
The following exhibit shows the potential conflicts from having
driveways too close to median openings.


MEDIAN HANDBOOK

Source: NCHRP 420 Impacts of Access Management Techniques
- 1999

A study, “Determination of the Offset Distance between
Driveway Exits and Downstream U-turn Locations for Vehicles
making Right Turns Followed by U-turns” gives us some
guidance for the needed right turn offset or weaving distance
needed. See the following exhibit for a picture of the “offset
distance”.

Source: Determination of the Offset Distance between Driveway
Exits and Downstream U-turn Locations for Vehicles making
Right Turns Followed by U-turns –University of South Florida,
November 2005 - Jian John Lu, Pan Liu, and Fatih Pirinccioglu


MEDIAN HANDBOOK
Even though the study focused on the weaving made by vehicles
positioning for a U-turn, the distances recommended are
transferable since the movement to get into a left turn lane is the
same maneuver as the one for a U-turn. The research pointed to
the fact that the more lanes you have, and the existence of a
traffic signal necessitates longer offset distances to safely and
efficiently move the left of U-turning traffic.

Recommended Offset Distances from the
Research

Source: Determination of the Offset Distance between Driveway
Exits and Downstream U-turn Locations for Vehicles making
Right Turns Followed by U-turns –University of South Florida,
November 2005 - Jian John Lu, Pan Liu, and Fatih Pirinccioglu

Full Width Median Where at all possible, you should try to get the perception-
reaction distance as a full width of median. This allows a larger
portion of median which will be more visible to the driver. This
also gives more area for traffic signs and landscaping.


MEDIAN HANDBOOK
Deceleration and Length Taper — The Taper is the portion of the median opening that
of the Left-Turn Lane begins the transition to the turn lane. Standard Index #301
contains the standards for this feature.
Design standards for left turn lanes are available from several
sources, most of which base their rate of taper on approach speed;
the faster the speed, the longer the taper. The FDOT does offer
standards for the design of left turn lanes. The FDOT Standards
Index dictates the use of a 4:1 ratio for bay tapers on all multilane
divided facilities regardless of speed. This may be an abrupt
transition area, however, most urban areas will benefit from a
longer storage area. Urban speeds are generally lower which
lessens the need for gradual tapers.

Total Deceleration
Distance (Includes
Taper)
Florida DOT Standard Minimum standards for the distance needed to properly slow a
Index #301 vehicle down, and bring the vehicle to the storage portion of the
median opening is found in Standard Index #301. This distance is
measured from the beginning of the taper to the end of the queue
storage portion.

The standards found in the Standard Index however should be
considered a minimum because research has shown reactions vary
considerably with drivers. And in many cases, more space may be
needed.


MEDIAN HANDBOOK
MEDIAN OPENINGS SHOULD NOT BE IN FUNCTIONAL
AREA

2. 4 Design The design speed is the speed used to make critical decisions on
Speed/Entry Speed the roadway design features. The AASHTO Green Book defines
the design speed as:
“Design speed is the maximum safe speed that can be
maintained over a specified section of highway when
conditions are so favorable that the design features of the
highway govern.”
The Green Book also makes the following statements regarding
the design speed.
“Once selected, all of the pertinent features of the
highway should be related to the design speed to obtain a
balanced design. Above-minimum design values should
be used where feasible.” (emphasis added)


MEDIAN HANDBOOK
Entry Speed When considering medians and median openings, the greatest use
of design speed is for determining the length of right and left turn
lanes. A reading of the FDOT Standard Index #301 will show that
design speed or the related entry speed are the basis for
determining the minimum length of the turn lane for deceleration
and stopping behind the turn lane queue.

Deceleration Distances from the Design Standards
Index #301
Design Speed (MPH) Entry Speed (MPH) Total Deceleration (ft)
35 25 145
45 35 185
50 Urban 40 240
50 Rural 44 320
55 Rural 48 385

Total Deceleration The turn bay should be designed so that a turning vehicle will
Distance — Why Do We develop a speed differential (through vehicle speed minus the
Care About Deceleration entry speed of turning vehicle) 10 MPH or less at the point it
Distance? clears the through traffic lane. The length of the bay should allow
the vehicle to come to a comfortable stop prior to reaching the
end of the expected queue in the turn bay.

EXCESSIVE DECELERATION

If the turn bay is too short, or queued vehicles take up too much
of the deceleration distance, there will be excessive deceleration
in the through lane. This creates a high crash hazard as seen in
research.


MEDIAN HANDBOOK

CRASHES AND SPEED DIFFERENTIAL

Non-Peak Hour Speeds Non-Peak Hours are also important considerations since around
80% of the daily traffic takes place at that time, usually at higher
speeds. Turning volumes are lower at those times which will
make queuing requirements smaller.

For More Information on Speed Definitions:
• Design Speed, Operating Speed, and Posted Speed
Practices, NCHRP Report 504, 2003
• AASHTO Green Book

Queue Storage
Turn lanes must include adequate length for the storage of traffic
waiting to turn. This is also called turn lane queue length. Where a
specific queue study does not exist, the Florida Department of
Transportation will normally require a minimum of a 100 ft. queue
length (four passenger cars) in an urban/suburban area and a 50 ft.
(two passenger cars) queue length in rural or small town areas.
Sources:
• Plans Preparation Manual Vol. I - 2.13.2 Queue
Length for Unsignalized Intersections
• Median Opening and Access Management
Decision Process (FDOT) Topic No.: 625-010-020

The AASHTO Green Book suggests the use of a 2 minute interval
for unsignalized locations. The following Figure illustrates that
where the average queue is 2 vehicles, the actual queue will
probably be over 2 vehicles much of the time.


MEDIAN HANDBOOK

HOW CAN DESIGNING TO THE AVERAGE FAIL?

The technique used to analyze this distribution of queue length is
the Poisson Distribution. The Poisson Distribution is used to
predict randomly occurring discrete (i.e., 0, 1, 2, 3, etc.
occurrences) events such as queues. Using this statistical
technique we see that building queue storage to fit the average
means you will “fail” 30% to 40% of the time.
QUEUE STORAGE

You should recognize that application of the Poisson
Distribution to queue storage length problems assumes that
all vehicles arriving on a cycle (or in a specified interval) clear
the intersection on that interval. The Poisson Distribution
should not be used where one or more vehicles do not clear the
intersection and must wait for the next interval. Queue storage
where such “carry over” from one cycle to another involves much
more complicated analyses. Using Poisson Distribution you can
determine the queue length necessary to have "success" 90% of
the cycles (usual standard).


MEDIAN HANDBOOK
Rule of Thumb: Design queues are usually

1.5 to 2 times the average.
The following table contains the recommended queue storage
length of as variety of left turn volumes. The recommendations
were based on a 90% success rate for non-SIS/FIHS facilities and
95% for the FIHS. You must consider the historic variability of
these numbers, as well as the inherent inaccuracies of traffic
projection models when making your recommendation. When
possible and desirable get more storage where projections seem to
be “light”.

Recommended Queue Storage for Unsignalized
Median Openings

Lefts per Hour Recommended Recommended Queue
Queue ( SIS/FIHS)
(non SIS/FIHS)
30 2 3
(only in small towns (only in small towns or
or rural areas) rural areas)
40 3 4
(only in small towns
or rural areas)
50 3 4
60 4 5
70 4 5
80 5 6
90 5 6
100 6 7
110 6 7
120 7 8
130 7 8
140 7 8
150 8 9

Assumptions: 120 second interval, Approximate probability of success is 90% non-FIHS and
95% SIS/FIHS


MEDIAN HANDBOOK
Queue Length The length of 25 feet is an average distance, front bumper-to
Adjustments for Trucks bumper of a queue. If the queue is comprised mostly of passenger
cars, this distance provides for an average distance between
vehicles of about one-half car length.

If 5% or more large vehicles are expected, the average queue
length, including gap, per vehicle should be increased as follows:
ADJUSTMENT FOR LARGE VEHICLES
Percent Average Storage
Trucks Length per Vehicle
5% 27 ft
10% 29 ft
15% 32 ft
20% 35 ft
Source: Adapted from Transportation and Land Development,
Stover and Koepke
Use Caution Near Railroad
Crossings Use caution to assure that queues will not be placed over
downstream railroad crossings. Railroad crossings should not be
anywhere near the functional area on an intersection.

For more information on Queues, Storage, and Projecting Left
Turns:
• AASHTO Green Book
• FDOT Project Traffic Forecasting Handbook, Statistics
Office,
• Volume Warrants for Left-Turn Storage Lanes at
Unsignalized Grade Intersections, M.D. Harmelink
• For Signalized Intersections: Storage Requirements for
Signalized Intersections Approaches, Joseph and Jane
Oppenlander, ITE Journal, Feb. 1996

Median Opening
Spacing — How All
These Factors Impact The spacing of median openings will be the sum of the following
the Spacing of factors for both directions of the roadway.
Openings


MEDIAN HANDBOOK
• Deceleration
• Queue Storage
• Turn Radius (usually 60 feet)
• Perception/Reaction distance or Full Width of Median
- The length of the median which is not a part of the turn
lanes or the taper. These sections provide for visibility,
buffer and landscaping opportunity.

A REALISTIC MINIMUM URBAN
Design Speed – 45 mph SCENARIO
Suburban Location

Left Turn Queue Storage
(Signalized) = 350 ft
Deceleration = 185 ft

Left Turn Queue Storage
(Unsignalized) = 100 ft
Full width median = 130 ft
Turn Radii = 60 ft

WHY IS ½ MILE SPACING SO GOOD?

Space for:
• Safety
• Operations
• Flexibility
• Signal Progression
• Aesthetics


MEDIAN HANDBOOK

2.4
WHAT DISTANCE IS
NEEDED FROM A Observations indicate that drivers tend to make erratic maneuvers
FREEWAY RAMP when there is a limited separation between the gore area of the
TERMINAL TO THE off-ramp and the median opening, drivers will make erratic
FIRST MEDIAN maneuvers as illustrated. Desirable conditions would permit a
OPENING? driver to accelerate, merge into the outside traffic lane, select an
acceptable gap in order to merge into the inside lane and then
move laterally into the left-turn lane and then come to a stop as
illustrated.

SPACE NEEDED BETWEEN FREEWAY OFF-RAMP AND
MEDIAN

We already have sufficient guidance on the distance needed for
queues and deceleration. Determining the appropriate distance for
the weaving portion of this maneuver may be accomplished
through a technique developed by Jack Leisch in Procedure for
Analysis and Design of Weaving Sections (FHWA Project -
1982). The procedure was developed to determine weaving
distances from freeway ramps to intersections on frontage roads.
This technique as adapted by Joel Leisch, is transferable to the
analysis of weaving on to an arterial road.

This weaving distance may be determined by.
• conflicting weaving vehicle flows
• desired running speed of the weaving vehicles

The next figure shows how conflicting movements are
determined.


MEDIAN HANDBOOK

The total volumes for conflicting crossing (not simply weaving)
streams are as follows:
Movement Volume
2 150
3 250
4 150
5 650
Total 1,200
If you wanted to design for a weaving speed of 35 mph you
would use the following graph going up the left side to 1,200 and
then going to the right until you get to the 35 mph line. Then you
would follow the line down to the bottom of the graph to read
approximately 600 feet. Experience shows that most urban
situations fall within 800 to 1,600 conflicting weaving
movements in the peak hour. If we design for a weaving running
speed between 35 and 45 mph, we see that the weave section
should be between 400 to 1,600 feet.


MEDIAN HANDBOOK
Experience shows
that most urban
situations fall within
800 to 1,600
conflicting weaving
movements in the
peak hour. If we
design for a
weaving running
speed between 35
and 45 mph, we see
that the weave
section should be
between 400 to
1,600 feet.

These measures is strictly the minimum weaving and maneuver
IMPORTANT distance from the end of the ramp to the beginning of the
POINT deceleration area of the interchange not to the median opening or
traffic signal.
This technique is most useful in unsignalized off ramp situations.
If the ramp is signalized, this weaving distance will need to be
determined by a signal spacing analysis.


MEDIAN HANDBOOK

2.5
MEDIAN END The median end design for an urban arterial should be designed
TREATMENTS for a passenger vehicle while assuring it can accommodate a
larger design vehicle. Different median ends can be used.
Alternative designs are semicircular, symmetrical bullet nose,
asymmetrical bullet nose, half-bullet nose, but remember:
always use turn lanes.

The only new openings that will be provided without turn
lanes would be for official or emergency use only.

Problem A Strictly Bullet Nose Opening

The “bullet nose” median opening requires a vehicle to make a
left turn from a through traffic lane (see next figure) interfering
with the through traffic. This will result in a situation with a high
potential for rear-end crashes.

POTENTIAL CRASH PROBLEMS WHEN LEFT-TURN IS
MADE FROM THE THROUGH TRAFFIC LANE

Solution
The only way in which left-turn vehicles can be removed from a
through traffic lane is to install a left-turn bay (see next Figure).
The lane should be of sufficient length to allow for adequate
maneuver distance plus queue storage as discussed in Chapter 2.
The total length of the left-turn deceleration lane, including the
taper, should be sufficient to allow the turning vehicle to
decelerate from the speed of through traffic to a stop plus queue
storage. Existing bullet nose, median openings should be replaced
with a left-turn lane.


MEDIAN HANDBOOK

LEFT-TURN LANE TO REMOVE LEFT-TURN
VEHICLES FROM THE THROUGH TRAFFIC LANES

2.5
MEDIAN OPENING The Department has historically used 60 ft for most situations and
LEFT TURN RADIUS 75ft when significant truck volumes are expected.


MEDIAN HANDBOOK

2.6
MEDIAN OPENING
LENGTH Median opening length is governed by the
• Turn radii
• Side street geometrics
• Median (traffic separator) width
• Intersection skews
• Intersection legs
Problem: Excessively Wide Median Opening

An excessively wide median opening will store two or more
vehicles in an unsignalized full median opening while they are
waiting to complete a maneuver results in multiple conflicts for
both the turning vehicles and through traffic. The situation shown
results at full median openings on high volume roads during peak
periods. This often occurs in areas where development has
occurred and traffic volumes substantially increased since the
median opening was originally constructed.
VEHICLES STOPPED IN EXCESSIVELY WIDE MEDIAN OPENING

Solutions: Alternative solutions to the problem are:
1) Reconstruct the unsignalized full opening as a more
restrictive median opening.
2) Close the median opening.


MEDIAN HANDBOOK
Which solution is selected, as well as the design of the restrictive
movement if used, will depend upon such things as proximity to
other median openings, alternative routes, traffic volumes and
crash experience.
The presence of several vehicles in the median opening results in
impaired sight distance, especially when one or more of the
vehicles is a pickup, van, or RV. Signalization should be
considered only if the median opening otherwise conforms to
signalized intersection standards.

For More information on Median Opening Length:
• AASHTO Green Book Median Openings Section of "At-
Grade Intersections”
2.7
PAVEMENT MARKINGS The Manual on Uniform Traffic Devices (MUTCD) contains
AND SIGNING guidance on the type and placement of signs and traffic control
devices at median opening areas.

Excerpt from the lower portion of M.U.T.C.D. figure 2-3a

This is an example for signing on extra wide medians in
rural areas.


MEDIAN HANDBOOK

Sight Distance 3

Source: Florida Highway Landscape Guide - 1995
SIGHT DISTANCE AS IT RELATES TO MEDIANS AND
MEDIAN OPENING DESIGN
This chapter addresses sight distance issues related to
3.1 unsignalized median openings and roadway connections. The
INTRODUCTION TO bulk of the chapter contains discussion of the assumptions
SIGHT DISTANCE relating to stopping and intersection sight distances. We use
CONCEPTS AASHTO Green Book as a basis for much of the Florida
standards. Right turn and passing sight distance is not addressed
because they are not normally an element in median opening
location and design.

Highways must be designed to provide sufficient sight distance so
that drivers can control and safely operate their vehicles. The
following sight distances are of concern on median and median
opening decisions, both urban and rural.
• Stopping Sight Distance: The distance necessary for the
driver to safely bring a vehicle to a stop.
• Intersection Sight Distance: The distance necessary for
drivers to safely approach and pass through an
intersection.


MEDIAN HANDBOOK
• Height of Eye - In determining sight distance, the height
of the eye of the person who must stop or pass through the
intersection is assumed to be a certain measure. This
assumption has significant bearing on such issues as the
placement of landscaping which might obstruct the view
of the vehicle at the assumed height.
• Height of Object - AASHTO assumes a determined
height of object for intersection sight distance. This will
allow the driver to view the headlights of an oncoming
passenger car.

AREA SIZE OF VEHICLE
Florida DOT has developed criteria for sight distance that allows
a 50% “Shadow” control for sight DISTANCE. This means that if
a driver can see at least 50% of the visual area of a vehicle it is
considered “visible”.

TIME OF VISIBILITY
Where visibility is blocked by over 50%, the Department will
allow for two seconds unobstructed visibility.

WHAT IS STOPPING Sight distance is the length of roadway ahead visible to the driver.
SIGHT DISTANCE? The minimum sight distance available on a roadway should be
sufficiently long to enable a vehicle traveling at or near the design
speed to stop before reaching a stationary object in its path. The
sight distance at every point along the highway should be at least
that required for a below-average operator or vehicle to stop in
this distance.


MEDIAN HANDBOOK

Minimum Stopping Sight Distance (Feet)
Minimum Stopping Sight For application of stopping sight distance, use
Distance an eye height of 3.5 feet and an object height of
0.5 feet above the road surface

Design Speed Minimum Stopping
Sight Distance (feet)
35 250
45 360
55 495
60 570
65 645
Source: Plans Preparation Manual Vol. I
Table 2.7.1

3.2
SIGHT DISTANCE FOR
SPECIFIC MEDIAN
OPENING MANEUVERS

3.2.1 Right Turns and Left Design Standard Index #546 specifies the following sight
Turns on Divided Roadway distances for right and left turns at intersections on multi-lane
roads with medians. These should be considered minimums. The
following figure shows an example at 45 mph with a 22 ft median
width.


MEDIAN HANDBOOK

590 Feet (with a 22 ft median)

Intersection Sight Distance by
Design Speed
Design Speed Intersection Sight Distance
(mph) (Feet)

25 to 64 ft
22 ft Median
median*
35 460 330
45 590 430
55 720 530
60 780 570

• If the median width is over 25 feet, than the passenger car
(P) can make the maneuver as a two-step process
Source: Design Standard Index 546

Turning left through a For divided highways with medians (the median is wider than the
Median as a Two-Step length of the design vehicle plus front and rear clearance), the
Maneuver maneuvers can be performed as two operations. The stopped
vehicle must first have adequate sight distance to depart from a
stopped position and cross traffic approaching from the left. The
crossing vehicle may then stop in the median prior to performing
the second operation. The second move requires the necessary
sight distance for vehicles to depart from the median, to turn left
into the cross road, and to accelerate without being overtaken by
vehicles approaching from the right.


MEDIAN HANDBOOK
Sight Distance for U- U-Turns are more complicated than simple turning or crossing
Turns maneuvers. Knowing this, sight distances for U-Turns were
calculated for automobiles with the following assumptions:
• “P” vehicle (Passenger vehicle)
• 2.0 seconds reaction time
• Extra time spent in the u-turn maneuver
• Begin acceleration from 0 mph only at the end of the U-
Turn Movement (this is conservative)
• Use of speed/distance/and acceleration figures from
AASHTO Green Book 1990, Figures IX-34 pg. 749
• 50 feet clearance factor

HOW A U-TURN SIGHT DISTANCE WAS CALCULATED

Sight Distance for Left In most cases the right turn sight distance from the side street
Turn into Side Street would control the sight distance of this area. If the area has
enough sight distance to allow a right turn vehicle from the side
street, the sight distance should have sufficient sight distance for
the vehicle turning left from the median into the side street.

Left Turn Lane Offset Vehicles turning left from opposing left turn lanes restrict each
other's sight distance unless the lanes are sufficiently offset.
Offset is defined as the lateral distance between the left edge of a
left turn lane and the right edge of the opposing left turn. When
the right edge of the opposing left turn is to the left of the left
edge of the left turn lane, the offset is negative as shown. If it is to
the right, it is a positive offset as indicated below.


MEDIAN HANDBOOK
Desirable offsets should all be positive with a recommended
minimum 2-foot offset when the opposing left turn vehicle is a
passenger car and a recommended minimum 4-foot offset when
the opposing left turn vehicle is a truck. In both cases the left turn
vehicle is assumed to be a passenger car.
From Plans Preparation On all urban designs offset left-turn lanes should be used with
Manual median widths greater than 18 feet. A four foot traffic separator
should be used when possible to channelize the left turn and
provide separation from opposing traffic. On rural intersections
where high turning movements are involved, offset left-turn lanes
should also be considered.

On median widths 30 feet or less, an offset turn lane parallel to
the through lane should be used and the area between the left turn
and traffic lane where vehicles are moving in the same direction
should be striped out. On medians greater than 30 feet, a tapered
offset should be considered.
Source: Plans Preparation Manual Vol. I, 2.13.1


MEDIAN HANDBOOK

For More Information on Offset:
• District 1 Access Management Unsignalized Median
Opening Guidelines
• Transportation Research Record #1356


MEDIAN HANDBOOK

3.3
LANDSCAPING AND
SIGHT DISTANCE
ISSUES
Two important Florida Department of Transportation documents
address landscaping as they relate to medians:
• Standard Index #546 (Sight Distance)
When the number of
• “Florida Highway Landscaping Guide” (FDOT,
median openings
Environmental Management Office)
and driveway
connections are
reduced, a greater The Landscape Guide States the Importance of Access
area is generally Management in Providing Good Visibility and Landscaping
available for Opportunities:
landscaping.
“Access management is the management of vehicular access
to the highway. This includes ingress to the highway, egress
from the highway and median openings on divided highways.
A well-designed highway with good access management can
be aesthetically pleasing. It provides the landscape architect
greater opportunity in the development of practical and
efficient landscape plans. When the number of median
openings and driveway connections are reduced, a greater
area is generally available for landscaping. The reduction of
median openings and driveways also reduces the number of
locations that must meet clear sight requirements. This
allows greater flexibility in the landscape plan. Therefore,
any plan for landscaping a highway should consider access
management.”

Major Criteria for Decisions • Sight Distance - for left turns as stated in Standard Index
on Sight Distance and #546
Planting Area and Spacing • Stopping Sight Distance (for absolute clear area)
in Medians • Tree Caliper – 4 – 11 in. and greater than 11 in. to 18 in.
• Tree Spacing - as stated in Standard Index #546
• Area Size of Vehicle Seen - 50% coverage or 2 seconds
of complete visibility
• Horizontal Clearance - as stated in Standard Index #700
or Plans Preparations Manual
• Clear sight window criteria - see next Figure.


MEDIAN HANDBOOK
Why are the same standards used for both signalized and
unsignalized intersections?
• Signal can malfunction
• Signal can go to flashing mode

5’
1’ 6”

3’ 6”

median landscape sight window.ppt
Source: Adapted from the Florida Highway Landscape Guide,
Environmental Management Office, 1995

Tree Spacing Guidance – Standard Index 546


MEDIAN HANDBOOK

The spacing of trees is based on the design speed and the caliper
of the tree trunk. Once the caliper of the tree trunk is over 18", the
driver can completely loose sight of the other vehicle, therefore,
the spacing of the trees increases dramatically to allow a complete
2 second view between trees.

Areas Limited to Ground
Cover Standard Index 546 also has important direction on areas that
should never have any landscaping except low groundcover. At a
minimum, it should be stopping sight distance or to the start of
the turn lane taper (whichever is the longest measure)


MEDIAN HANDBOOK

Trees In Median Intersection Sight Corridor
And Outside Clear Zone (6' Horizontal
Clearance), Curb And Gutter

For More Information on Landscaping and Sight Distance:
• Florida Highway Landscaping Guide, FDOT -
Environmental Management Office (1995)
• AASHTO Green Book (1990), pg. 739
• Standard Index #546 (Sight Distance at Intersections)


MEDIAN HANDBOOK


MEDIAN HANDBOOK

Median Width
4

MEDIAN WIDTH
4.1
Function Determines
Median Width
The appropriate median width is a function of the purpose which
the median is to serve in a particular application. Applications on
roadways having at-grade intersections which affect median
width include the following:
• Separate opposing traffic streams
• Pedestrian refuge
• Left-turn to side street
• Left-turn out of side street
• Crossing vehicles
• U-turns
• Aesthetics and maintenance


MEDIAN HANDBOOK

4.2
ANATOMY OF MEDIAN
WIDTH

Important Point:
Never use the gutter
space as part of
your turn lane
width.

Median width in most urban situations is made to accommodate
turning lanes and a separator. The width of both the lane and
separator are critical to the operations of the median opening.
4.3
Minimum and
Recommended Widths

SUMMARY OF STANDARDS AND RECOMMENDATIONS

Guidance Design Speed and Notes Width
(Feet)
Minimum Plans Preparation Manual (Reconstruction 15.5
Projects) = 40 mph and less
Minimum Plans Preparation Manual (Reconstruction 19.5
Projects) 45 mph
Minimum Plans Preparation Manual (less than 55 22
mph)
Guidance from
Plans When greater than 55 mph 40
Preparation
Manual
4 lane highways with medians expecting 30
Recommended significant u-turns and directional median for single
openings with excellent positive guidance left turns
42
for dual
lefts
6 lane highways with medians expecting 22
Recommended significant u-turn and directional median for single
openings with excellent positive guidance left turns
34
for dual
lefts


MEDIAN HANDBOOK
Where left turns are not expected due to terrain or land use, a
median as narrow as 6 feet can help channelize traffic and provide
more positive guidance and prevent unwanted left turns.
A critical function of many medians is to protect vehicles turning
left. The following figure shows how some narrow medians
cannot do this task.

4.4
SOME EXAMPLES

Median Width: 9m (30 ft) - DESIRABLE ASPECTS
What it does • Greater flexibility in the choice of lane widths and
separation width at double left-turn, full median openings.
• Additional width for landscaping the overlapping “traffic
separators” at directional median openings.
• Permits separate vertical and/or horizontal alignment of
the two roadways.

For more information on Turn Lane Width:
• Plans Preparation Manual Table 2.1.1


MEDIAN HANDBOOK

4.5
MINIMUM TRAFFIC The minimum width of a median traffic separator "nose" has
SEPARATOR WIDTH AT commonly been 4 ft. Where the right-of-way is limited, 2 ft and
INTERSECTIONS even as little as 18 in. has been used. AASHTO indicates that “...
the minimum narrow median width of 4 ft is recommended and is
preferably 6 to 8 ft wide.” (AASHTO Green Book). The 1994
edition included the same statement with 1.2m minimum and
preferable widths of 1.8 to 2.4m (p. 786).

4.6
PEDESTRIAN Pedestrian refuge minimum for common practice is to use a
CONSIDERATIONS AT minimum of a 4 ft separator between the left-turn lane and the
TRAFFIC SEPARATORS opposing traffic lane. The minimum width for pedestrian refuge is
6 ft. Where more than occasional pedestrians may be present, the
median width should be at least 8.5 ft and preferable at least 10 ft.

4.7
SEEING TRAFFIC Very narrow median noses are very difficult to see, especially at
SEPARATORS AT night and in inclement weather. Reflectorized paint is of little
INTERSECTIONS help as it rapidly becomes dirty and loses its limited reflectivity.
Reflectorized traffic buttons and/or reflectorized pylons help but
lack the “bulk” to provide good “target value”. Carefully selected
landscaping is the only effective way to provide excellent
visibility of the median and median openings. A minimum traffic
separator width of 6 ft and preferable 8.5 ft. is needed for the
median nose to be of sufficient width back-to-back of curbs to
provide adequate area for vegetation to make it highly visible.
Landscaping of the median nose to provide visibility is especially
important where long left-turn lanes are used. Obviously the
choice of vegetation and the landscaping design must ensure that
sight distance is not obstructed.

4.8
MINIMUM MEDIAN SEE CHAPTER 5 FOR COMPLETE ANALYSIS
WIDTH FOR U-TURNS
U-turns should not be permitted from through traffic lane because
of the potential for high speed, rear-end crashes and serious
detrimental impact on traffic operations. Rather all left-turns, and
u-turns should be made from a left-turn/u-turn lane.
Extremely wide medians are needed for a u-turn by all design
vehicles other than the P-vehicle, the P-vehicle can not make a u-


MEDIAN HANDBOOK
turn on a 4-lane divided roadway with curb and gutter and
commonly used median nose widths. A very high percentage of
the automobile fleet is intermediate and smaller than the "P"
design vehicle. Small or intermediate vehicles can complete a u-
turn on a 4-lane divided roadway having curbs and gutters and a
2m (6 ft) median traffic separator nose.
The design P-vehicle can make a u-turn on a 4-lane divided
roadway with a 6 ft. median nose by “flaring” the receiving
roadway.

4.9
DESIGN FOR TRUCKS See chapter 5 for a more complete discussion of truck U-turns
The extremely wide median that is required for buses and trucks
to make a u-turn makes it impractical to design for these vehicles
except in exceptional cases. The need for u-turns by large
vehicles can generally be avoided in the following ways:
(1) Bus routes can be laid out so as to eliminate the need for u-
turns on a major roadway.
(2) Driveway connections can be located and on-site circulation
designed to eliminate the need for u-turns by trucks.


MEDIAN HANDBOOK


MEDIAN HANDBOOK

Special U-Turn Considerations
5

SPECIAL U-TURN CONSIDERATIONS

5.1
AASHTO GUIDANCE ON
WIDTH AND U-TURNS
The AASHTO GREEN BOOK contains some guidance on the
relation between median width and u-turn movements.
Unfortunately, the figure in the Green Book shows the u-turn
movements made from the inside (left) lane. This is contrary to
the basic principle of having left turns made in auxiliary lanes
rather than through lanes. Therefore, you need to add at least 12
feet to the width for this purpose. The next figure shows the
AASHTO Green Book figures with 12 feet added for a better
guide to median width and u-turns. As you can see, in order to
make the width sufficient for a Passenger Car (P) to make a u-
turn from the turn lane to the outer lane, it would require 30 feet.
If you cannot provide 30 feet, then the car will encroach on to the
shoulder. This is okay as long as this encroachment has been built
into the design. When designing for 6 lane highways, 20 feet of
median width will usually provide sufficient space for the u-turn
for the passenger car (P) vehicle.


MEDIAN HANDBOOK

IMPORTANT: The “P” vehicle is
approximately the size of a luxury car or a
Chevy Suburban. Therefore, many vehicles
in today’s passenger car fleet can make
tighter u-turns.

5.2 In order to handle u-turns there are essentially three options
OPTIONS FOR U-TURNS available:
1. Wide medians

2. Median “Bulb-Out”


MEDIAN HANDBOOK
3. Flare-Out (Jug Handles)

Each of these options has their strengths and weaknesses. Traffic,
land use and terrains will play important roles in the decision on
their options.

Two Examples of a Flare The design P-vehicle can make a u-turn on a 4-lane divided
roadway with a 6 ft. Traffic separator by “flaring” the receiving
roadway or where a far-side bus stop is used, the u-turn can be
accommodated as illustrated in the following Exhibits.


MEDIAN HANDBOOK


MEDIAN HANDBOOK

5.3
TRUCK U-TURNS Special consideration for truck u-turns is usually not a major
consideration.
These special The extremely wide median that is required for buses and trucks
designs will to make a u-turn makes it impractical to design for these vehicles
probably only be except in exceptional cases. The need for u-turns by large
necessary at, or vehicles can generally be avoided in the following ways:
near, truck facilities, • Bus routes can be laid out so as to eliminate the need for
major industrial u-turns on a major roadway.
areas, or truck • Driveways can be located and on-site circulation designed
staging areas. to eliminate the need for u-turns by trucks.
• Local governments can avoid the need for u-turns by large
vehicles through their subdivision, and site development
ordinances.
Alternatives for U-TURN DESIGNS FOR LARGE VEHICLES
accommodating u-turns by
large vehicles (such as
delivery, trucks and semis)

In most cases Option "A" would need a signal. Option "B" has the
following desirable operational features.
• The u-turning vehicle is stored in the median parallel to
the through traffic lanes.
• A suitable gap is needed in the opposing traffic stream
only.
• After completion of the u-turn the driver can accelerate
prior to merging into the through traffic lane.
These options require more right-of-way than most standard
highway designs, but it may be designed into our highway
corridors where public land is available such as parks,
government maintenance facilities, etc. These truck u-turns might
be most helpful on our Florida Intrastate Highway corridors


MEDIAN HANDBOOK

Jug-handle at a Miami horse race track specifically designed for
horse trailers

5.4
U-TURN LOCATIONS

U-Turn at Signalized Where medians are of sufficient width to accommodate dual left-
Intersections turn lanes, an excellent option is to allow u-turns from the inside
(left-most) left-turn bays as illustrated.
U - turns at signal when:
• Median is of sufficient width
• Low combined left-turn plus u-turn volume at signalized
single left-turn .

You should note:
• Consider "right-on-red" restrictions for side streets
• Remember to look at signal operation
• Don't let the signalization work against U-turns


MEDIAN HANDBOOK
Right turn on red restrictions
may be necessary on the
side streets to minimize
conflicts with U-turns.


MEDIAN HANDBOOK

U-Turns in Advance of A u-turn in advance of a signalized intersection will result in two
a Signal successive left-turn lanes as illustrated in the figure. Unless there
is a substantial length of full median width, drivers may
mistakenly enter the u-turn lane. And realizing their mistake,
make an abrupt re-entry into the through traffic lane. Over one
hundred feet of full median width would help avoid this problem.
If 100 feet is not possible, signage or other markings can be used
to help guide the driver.

Indications that you should consider a U-Turn opening before a
signal are:
• Level of Service problems at intersection
• Heavy left turns currently at signal
• High conflicting right turn
• Lanes at signalized side street (where restrictions would
hurt)
• Where gap of oncoming vehicles would be beneficial at
separate u-turn opening
• Where there is sufficient space to separate signalized
intersection and opening
A Study on U-turns by the
University of South Florida
has shown that having u-
turns made before a
signalized intersection can
greatly decrease delay at the
signal.

Source: Safety And Operational
Evaluation Of Right Turns
Followed By U-Turns As An
Alternative
To Direct Left Turns, Dr. John Lu,
University of South Florida


MEDIAN HANDBOOK
U-turn Before Signal

U-turn Before Signal

U-Turn After Signal Locating the u-turn after a traffic signal has the same separation
issues as the U-Turn located before a signal. There should be
sufficient space to assure left and U-turns don't become confused
on the location of their turn lanes. These have been very popular
in Michigan and they are called “Michigan U-turns” or “Michigan
Lefts”


MEDIAN HANDBOOK
Michigan U Turn Aerial

Source: Maryland State
Highway Agency

Depiction of a proposed
“Michigan U- turn proposed
in North Carolina

Source: North Carolina DOT


MEDIAN HANDBOOK

5.5
PLACEMENT IN
Access connections should be located directly opposite or
RELATION TO
downstream from a median opening as illustrated. Driveway
DRIVEWAYS access should be located more than 100 upstream from the
median opening to prevent wrong way maneuvers as seen in the
figure.
ENTRY MANEUVERS


Median Handbook

More Related Content

Similar to Median Handbook (20)

Median Handbook