Lecture 03 Intersection Control (Traffic Engineering هندسة المرور & Dr. Usama Shahdah)

TRAFFIC ENGINEERING COURSE
(PWE 8322)
Instructor: Usama Elrawy Shahdah, PhDLecture # 02

Intersection Control
2
 References
Roger P. Roess, Elena S. Prassas, William R. McShane-
Traffic Engineering
 Chapter 16 in the 3rd edition
 Chapter 18 in the 4th edition

Conflict points at Un-signalized intersections
T intersection
Crossing = 3
Merging = 3
Diverging = 3
Total = 9
4-leg intersection
3

TWO Factors affecting a driver’s ability to
avoid conflicts
4
 A driver must be able to see a potentially
conflicting vehicle or pedestrian in time to
implement an avoidance maneuver, (sight
distance related) and
 The volume levels that exist must present
reasonable opportunities for a safe maneuver
to take place (gap availability related).

The Hierarchy of Intersection Control
 Level
I
Passive control – basic rules of the road apply
 No control
 Guide signs only
 Warning signs with or without guide signs
 Level
II
Direct assignment of ROW to major street or rotational ROW
 YIELD control (roundabouts are in this category)
 Two-way STOP control
 All-way STOP control
 Level
III
Positive alternate assignment of exclusive ROW
Traffic signals: 2-phase, multiphase
 Traffic control agent/officer
5

18.1 Level I Control: Basic rules of the Road
Primary prerequisite for safety under basic rules-of-the-road: Sight distance must
be adequate for the driver before he/she is accountable for full responsibility for his
action.  The first thing you want to check is whether adequate SSD is available at
the intersection. This must be satisfied before traffic volume concerns come into
consideration.
bd
ad
d
d
bd
abadab
da
bd
ab
ad
bd
ab
a
bd
ad
b
A
A
B
B
A
A
B
A
B
A
A
B











From the similarity
of triangles (1-3-
2 and 6-4-5):
“Visibility Triangle: Veh A is on minor street”
How do you
determine dA
and dB?
6

Rule 1: Both vehicles have at least one safe SSD to the collision
point (AASHTO recommended)
Step 1: Assume that Vehicle A (on minor street) is located one safe SSD from
the collision point. Usually the vehicle is considered to be on the minor road.
Step 2: Based on the assumed position, determine the
actual location of Vehicle B when it first becomes visible.
Call it dB(act)
Step 3: Rule 1 requires Vehicle B (on major street) to have one safe SSD.
Call it dB(min).
Step 4: If dBact > dBmin, then adequate SSD for basic rules-of-the-road has been
provided. Otherwise, violated and under Rule 1, not safe.
 G
S
tSd A
AA
01.0348.030
47.1
2


bd
da
d
A
A
B


 G
S
tSd B
BB
01.0348.030
47.1
2
min


7

Rule 2: Vehicle A must travel 18 feet past the collision
point in the same time that Vehicle B travels to a point 12
feet before the collision point
  (min)1218
468.1
12
468.1
18
B
A
B
AB
B
B
A
A
d
S
S
dd
S
d
S
d




This dB is used in Step 3 in Rule 1.
Step 4 is the same as Rule 1.dA
dB
8

When dBact < dBmin then operation with no
control cannot be permitted.
 Implement intersection control, using STOP- or YIELD-control, or traffic
signals.
 Lower the speed limit on the major street to a point where sight
distances are adequate.
 Remove or reduce sight obstructions to provide adequate sight
distances.
9

Sample problem: Fig. 18.3, p.412
Step 1:
Step 2:
Step 3:
Step 4:
ftdA 5.196
)348.0(30
)30(
)5.2)(30(47.1
2

ft
bd
ad
d
A
A
Bact 4.25
425.196
)5.196)(20(





ftd
ftd
RB
RB
0.29812
30
40
)185.196(
3.300
)348.0(30
)40(
)5.2)(40(648.1
2min,
2
1min,


dBact << dBmin,R1 and dBmin,R2
Both rules were violated.
dA
dB
The sight triangle between Vehicle A and B
fails to meet the criteria for safe operation
under basic rules of the road.
10
a
b

18.2 Level II Control: Yield and STOP Control
11
YIELD or STOP
control?
If the critical
approach speed
(CAS) is between 10
to 15 mph, use
YIELD.
If less than 10 mph,
use STOP.

Stop Control: Sample
Problem: Figure 18.4
18ft = (10 ft from the edge of
curb to the stop line) +
(8 ft form the front bumper to the
driver)
dA-STOP = 18 + dcl
dBmin = 1.47*Smaj*tg
13
dcl = Distance from the curb line to the center of
the closest travel lane from the direction under
consideration (ft): cl = curb line. (because LTs
must enter the median lane.)
bd
ad
d
A
A
B


(Eq. 18-5)
dA-stop(from left) = 18.0 + 6.0 = 24.0 ft
dA-stop(from right) = 18.0 + 18.0 = 36.0 ft
The minimum sight distance requirement for
Vehicle B is determined using a time gap ( tg) of
7.5 s for typical conditions.
dB min =1.47*40*7.5 = 441 ft
Now the actual distance of Vehicle B from the
collision point when visibility is established is:
For most STOP-controlled intersections, the design
vehicle is the passenger car, and the criteria for left
turns are used, as they are the most restrictive.
Trucks or combination vehicles are considered only
when they make up a substantial proportion of the
total traffic on the approach. Values for right-turn
and through movements are used when no left-turn
movement is present. For these typical conditions,
AASHTO recommends the use of tg = 7.5 s.

18.2.3 Multiway-way
stop control
16

18.3 Level III Control: Traffic Control Signals
18.3.1 Advantages of traffic signal control
 Provide for the orderly movement of traffic
 Increase the traffic-handling capacity of the intersection if
proper physical layouts and control measures are used
 Reduce the frequency and severity of certain types of
crashes, esp. right-angle collisions
 Provide for continuous or nearly continuous movement at a
definite speed when coordinated (by coordination)
 Used to interrupt heavy traffic at intervals to permit other
traffic, vehicular or pedestrian, to cross
17

18.3.2 Disadvantages of traffic signal control
 Excessive delay (when timing is improper)
 Excessive disobedience of the signal
indications (when red interval is improperly
long) – may encourage red-light running
 Increased use of less adequate routes as
road users attempt to avoid the traffic
control signal
 Significant increases in the frequency of
collisions (especially rear-end collisions)
18

1. Traffic volumes in each approach, at
least 12 consecutive hours (24 hrs
count preferred) containing the
highest % of 24-hour traffic (include
two peak periods)
2. 15-min counts by approach and
movement classified by vehicle type
during the 2 hours in the AM and
PM peak periods (4 hours total)
3. Pedestrian counts in each crosswalk
during the same 4 hours in item 2
4. Information on nearby facilities and
centers serving the young, elderly,
or disabled
5. Posted or statutory speed limit
and/or the 85the percentile speed
6. A condition diagram (i.e. geometry)
(ch.11)
7. A collision diagram (ch.11)
8. For the two peak AM and two peak
PM hours:
a) Vehicle-hours of stopped delay
for each approach
b) Number and distribution of gaps
c) Speed limits
d) Pedestrian delays for at least two
30 minute peak pedestrian delay
periods
e) Queue lengths on STOP-
controlled approaches
18.3.3 Warrants for traffic signals: Data requirements
(See page 418 and 419.)
19

MUTCD has 9 warrants for a traffic signal. They are guides, not
specifications. Use professional judgments.
 Warrant 1: Eight-hour vehicular volume
 1a: minimum traffic volume;
 1b: interruption of traffic;
 1c: combination of warrants)
 Warrant 2: Four-hour vehicular volume
 Warrant 3: Peak hour
 Warrant 4: Pedestrian volume
 Warrant 5: School crossing
 Warrant 6: Coordinated signal system
 Warrant 7: Crash experience
 Warrant 8: Roadway network
 Warrant 9: Intersection near a highway-rail crossing
Warrants for Traffic Signals
20

Signal warrant 1A: 8-hour volume
Min. vehicle volume: Principal factor is the intersection traffic volume. Must
satisfy for each of any 8 hour of an average day (they do not need to be
consecutive 8 hours).
May reduce the values by 30% if the 85th percentile speed on the major approach is
greater than 40 mph or population is less than 10,000 (built-up area of isolated
community).
21

Signal warrant 1B
Interruption of continuous traffic: The volume requirements must be met for
each of any 8 hours of an average day.
May reduce the values by 30% if the 85th percentile speed on the major approach is
greater than 40 mph or population is less than 10,000 (built-up area of isolated
community).
22

Signal warrant 1C
Combination of warrants: Only in exceptional cases.
When none of the warrants are satisfied but when
the first two warrants of Warrant 1 are satisfied to
the extent of 80% of the stipulated volumes.
23

Signal warrant 2: 4-hour volume
Check for each of any
4 hr of an average day.
To meet the warrant ,
at least four hours
must plot above the
appropriate decision
curve.
24

Signal warrant 3: Peak-hour volume
Justified where traffic
condition during 1 hr of
the day result in undue
(too much) delay to traffic
on the minor street.
25

Or Signal warrant 3B: delay
This applies to cases in which
STOP control is already in
effect for the minor road.
Cannot jump from no-control
or YIELD to signals.
26

Warrant 4: Pedestrians (4 hours)
27
(a) Normal criteria
(b) Pop < 10,000, major road
speed exceeds 35 mph
If a signal is warranted only by
this warrant, start with a
semi-actuated signal. A full
actuated signal is possible
at an isolated intersection.
Another one nearby < 300 ft?
Then, this warrant is not met.
May be reduced as much as by
50% if majority of walkers
walk at less than 3.5 mph.
Fig. 18-7

28
Or, Warrant 4: Pedestrians (peak hour)
Fig. 18.8

Warrant 5: School Crossing
29
 The warrant requires the study of available gaps to see whether
they are "acceptable“ for children to cross through.
 An acceptable gap would include:
 the crossing time,
 buffer time, and
 an allowance for groups of children to start crossing the street.
 The frequency of acceptable gaps should be no less than one
for each minute during which school children are crossing.
 The minimum number of children crossing the major street is
20 during the highest crossing hour.
 If only this warrant is met, use a pedestrian-actuated signal.

Warrant 6: Coordinated System
30
This should not result in
signal spacing of less than
1,000 ft.

Signal warrant 7: Crash Experience
 Less restrictive measures
must be used before this
warrant is used.
 5 or more injury or property-
damage-only accidents within
a 12-month period, AND
signal control is a suitable
countermeasure. AND,
 the traffic and pedestrian
volumes should not be less
than 80% of the requirements
of warrants 1A and 1B
31

Signal Warrant 8: Roadway Network
32
Warrant 8: Roadway Network.
When lights help to encourage
concentration and organization of
traffic networks.
(1) The total existing or
immediately projected volume
is at least 1000 during the
peak hour AND the 5-year
projected traffic volumes
satisfy the requirements of
one or more of the Warrants
1, 2, 3, on average weekday,
OR
(2) (2) The total existing or
projected entering volume is
at least 1000 vehicles for
each of any 5 hr of a
Saturday and/or a Sunday.

33
Signal warrant 9:
Intersection Near a
Highway-Rail Grade
Crossing

34
The minor-street volume used in entering either Figure18.9 or 18.10 may be multiplied by
up to three adjustment factors: (1) for train volume, (2) for presence of high-occupancy
buses, more than 20 passengers, and (3) for truck presence.
One lane approach

35
Two lane approach

36

A sample problem in application of signal warrants
39

Warrant 1
41
 There is no indication that the 70% reduction
factor applies
 Condition A or Condition B must be met at
100%, or both must be met at 80%
 Condition A is not met
 Condition B is met  no need to check C
 Warrant 1 is satisfied

Warrant 2
42
 Only one of the 12 hours of data is above the
criterion.
 To meet the warrant, four are required.
 Warrant 2 is not met.

Warrant 3
43
 None of the 12 hours of data is above the criterion.
 The volume portion is not met.
 Delay = 125 (The peak one-direction ) * 30
(sec/veh) = 3,750 veh-secs
 3,750/3,600 = 1.04 veh-hrs < 4 veh-hrs, which
required by the warrant.
 The delay portion is not met

Warrant 4
44
 The four-hour
pedestrian
warrant is met
 peak-hour
pedestrian
warrant is not met.
 Warrant 4 is met.
Four-Hour Pedestrian Warrant
Peak-Hour Pedestrian Warrant

Warrant 5
45
 The school-crossing warrant does not apply.
 This is not a school crossing.

Warrant 6
46
 No information on signal progression is given, so
 this warrant cannot be applied.

Warrant 7 (crash experience)
47
 Have lesser measures been tried? Yes, the minor
street is already STOP-controlled.
 Have five accidents susceptible to correction by
signalization occurred in a 12-month period? Yes,
four right-angle, three left-turn, and three
pedestrian.
 Are the criteria for Warrants 1A or 1B met to the
extent of 80%? Yes, Warrant IB is met at 100%.
 The crash experience warrant is met.

Warrant 8
48
 There is no information given concerning the
roadway network
 This warrant is not applicable

Warrant 9
49
 this situation is not a highway-rail grade crossing
location,
 this warrant does not apply.

Summary
50
 A signal should be considered at this location because the
criteria for:
 Warrant 1B (Interruption of Continuous Traffic),
 Warrant 4 (Pedestrians), and
 Warrant 7 (Crash Experience) are all met
 The fact that Warrant IB is satisfied may suggest that a semi-actuated
signal be considered.
 Warrant 4 requires the use of pedestrian signals at least for pedestrians
crossing the major street.
 If a semi-actuated signal is installed, it must have a pedestrian pushbutton
(for pedestrians crossing the major street).
 The number of left-turning accidents may also suggest consideration of
protected left-turn phasing

Home Reading
51
 Roger P. Roess, Elena S. Prassas, William R. McShane-
Traffic Engineering book
 Chapter 16 in the 3rd edition
 Chapter 18 in the 4th edition

Where do these
values come from?
My guess is…
Use the random
arrival case and use
the Poisson
distribution.
53

Lecture 03 Intersection Control (Traffic Engineering هندسة المرور & Dr. Usama Shahdah)

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