Robust Design of Parking Facilities

Parking planning is an integral part of modern transportation planning and, more specifically, that of urban development. The way in which parking space is provided affects land-use, choice of destination and mode of transport, quality of road transport, etc.

As the number of vehicles increases exponentially on a global level, the need to house them in close proximity to destinations creates a complex design challenge, whereby vehicle, engineering and traffic issues related to site locations must be integrated to create the appropriate solution. Designing a parking facility requires, therefore, an integrated approach.

Parking Space Planning and Analysis

Parking space planning and analysis shall include the following steps:

1. Estimation of parking demand and supply.

2. Design and construction.

3. Operation and use.

Parking supply is determined on the basis of a parking space demand forecast and should be compatible with the respective land-use and traffic conditions.

The result of the parking demand forecast is the future demand for parking space of the demand groups for individual time intervals during the day, possibly for different development scenarios. If the requirements of the individual demand groups are added, the total parking space requirement in the study area is obtained.

In the subsequent design and construction step, the geometry and design requirements are defined, which are specific to the use of the parking and loading areas, based on the dimensions of the relevant design vehicle. The connection to the public road network as well as their integration into the respective urban/rural development is also considered.

Finally, the use and operation step include the design of parking control systems, handling systems and signage, as well as the choice of an appropriate operating mode and features of specific uses.

Parking Facilities

Parking facilities are classified into three main types:

1. On-street parking spaces developed adjacent to the travelled lanes of a road.

2. Independent parking stalls developed off-street, at-grade as surface parking.

3. Parking structures (simple, multi-level) developed underground or over ground as parking garages.

Each facility consists of parking space(s) and aisle areas. In the case of on-street parking, the traffic lanes of the street also serve as the aisle.

Parking is permitted on highway and streets of specific functional classifications, such as collectors, local roads, etc.

All parking facilities shall be appropriately marked and signed

On-street parking lies within the public Right-of-Way (ROW). In urban areas and rural communities located on arterial highway routes, on-street parking should be considered in order to accommodate existing and developing land-uses.

Off-street parking facilities are those located outside the road ROW and account for the larger share of parking supply in any urban establishment. Off-street parking facilities can constitute at-grade surface facilities, simple structures or multi-level building parking structures (parking garages).

Parking Configurations

In principle, three types of parking configurations can be distinguished:

• Parallel.

• Angled.

• Perpendicular.

Parking parallel to the travelled lane is one of the most commonly used types in urban areas and appropriate for all streets. However, the parallel configuration is too complex to adopt in surface parking facilities and parking buildings. In general, it allows simple parking operations that are not particularly disruptive to the normal traffic flow. The disadvantage may be the potential obstructions during reverse parking in terms of increased parking demand and/or endangering cyclists and that entry and exit manoeuvres must often take place on shared spaces, with the traffic constituting a potential hazard.

The comparative advantage of angled parking is that this type of parking configuration provides a larger number of parking stalls compared to parallel parking. It also allows for easier manoeuvrability to enter the parking stall. For one-way roadways, angled parking should be preferred.

It is not recommended to use an angle smaller than 45°, as it would leave a larger area not used for parking or any other purpose. On the other hand, angled parking may present specific issues because of the varying lengths of certain vehicle types and related sight distances; longer vehicles may interfere with the travelled way. Also, parking in and out without the use of an additional lane is normally only possible at a small angle.

The perpendicular configuration allows for one-way or dual-way traffic; however, fast parking is not always guaranteed. 90° parking is not advisable along roadways with a median to avoid confusion of direction. In dead ends, the perpendicular position is preferred, so vehicles which have entered the dead end for parking can exit without any special turning manoeuvres. Nevertheless, in such cases, an additional lane should normally be used.

On-Street Parking

On-street parking areas for passenger cars can be either parallel or at certain angles. The parallel (longitudinal) parking configuration includes parking lanes and parking stalls. Parking lanes form part of the traffic space, provide better clearance from the travelled way and can be used during peak periods as through-travel lanes.

Parking stalls are positioned adjacent to the traffic space lateral boundary (which coincides with the paved edge line) and shall be designed at a height of approximately 0.05 m above the roadway surface.

In general, the following shall apply to on-street roadside parking:

• Longitudinal parking stalls should be preferred, parallel to the roadway, to reduce the areas appropriated for the ROW and save on road construction costs.

• Parking lanes should be used on local streets due to the narrow roadway width.

• In the angled or perpendicular parking configuration, an intermediate special lane shall be provided for manoeuvring to reduce the impact of exit/entry manoeuvres on the traffic on the roadway.

• Parking shall be prohibited within 4.0 m of either side of fire hydrants and allowed at certain distances from pedestrian crossings and intersections in order to maintain proper sight distance triangles, depending on speed and highway geometry.

Parallel parking

For both parking lanes and parking stalls, the distance allocated for parking shall not be less than 6.5 m in length and 2.5 m in width.

In order to prevent careless vehicle side door opening on the pedestrian sidewalk, a safety boundary of 0.75 m should be included, which will be formed by a lateral space of 0.25 m, adjacent to the vehicle, followed by a 0.5 m stripe width.

The accommodation of vehicles in parking stalls is generally preferable to the installation of parking lanes on the roadway, because they provide:

• Improved visibility for drivers at intersections and between drivers and pedestrians

• Reduced length of pedestrian and cyclist crossing paths

The beginning and end of parking lanes or parking stalls shall be determined at intersections, taking into account sufficient visibility distances.

In the case of high parking demand, parking spaces can be laid in an existing separating median to gain living space along the side spaces. The disadvantage is that users have to cross lanes on the way to their destinations.

The following criteria apply to the design of parking lanes:

• For a parking lane in a two-directional roadway with no median, the minimum traffic lane width in one direction shall be no less than 6.0 m, including 3.5 m of a traffic lane and 2.5 m of the parking lane.

• The parking space boundaries along parking lanes shall be clearly marked.

• At signalised intersections, the distance between the stopping line and the first parking space shall not be less than 9.0 m from the entrance to the intersection (6.0 m for non-signalized intersections). Also, parking spaces shall be positioned at a distance from marked or unmarked pedestrian crossings, the first parking space at least 6.0 m away from the crossing.

• If acceleration or deceleration lanes are included, the above distances shall be measured from the start of the tapered part to the first parking space from the entrance to the intersection, and from the end of the tapered part to the first parking space at the intersection exit.

The following criteria apply to the design of parking stalls:

• At signalised intersections, the distance between the stopping line and the first parking stall shall not be less than 15.0 m from the entrance to the intersection (6.0 m for non-signalised intersections). Also, parking stalls shall be positioned at a distance from marked or unmarked pedestrian crossings, the first parking stall at least 6.0 m away from the crossing.

• At intersections with secondary roads, the distances of the last parking stall before and the first parking stall after the intersection along the main roadway, shall not be less than 15.0 m and 6.0 m, respectively. The distance of the last parking stall before the intersection along the secondary road shall not be less than 6.0 m.

• The parking space boundaries along parking stalls shall be clearly marked

• In the case of acceleration or deceleration lanes, the above distances shall be measured from the last parking stall to the beginning of the tapered part at the entrance to the intersection and from the end of the tapered part to the first stall at the exit of the intersection.

• Long sections of continuous parallel parking stalls shall be interrupted by buildouts, e.g., for additional landscaping. This is to ensure empty parking will not be used as additional traffic lane, or to circumnavigate queues at traffic lights.

• It is advisable to allocate 5% of the number of parking spaces on commercial roads to electric cars, and the parking spaces be equipped with electric power sources for the purposes of charging cars.

Angled parking

In angled or perpendicular parking configurations, a special intermediate (manoeuvring) lane must be added to reduce the impact of vehicles manoeuvring on adjacent traffic lanes when entering and exiting the parking stalls. This type of parking requires additional width due to the obvious differences in vehicle lengths and the limited visibility of the vehicles when manoeuvring out of the parking stall; the latter increases with the angle of parking. A typical width for this manoeuvring lane is set to 2.00 m, however depending on the angle of the parking a swept path analysis shall be required.

Usually, angles of 45°, 60° or 90° (perpendicular parking) are used. Nevertheless, angled parking over 45°shall be used mainly on residential streets or combined with low traffic volumes in other areas. Notably, the number of perpendicular parking stalls along a specific length of a road is greater compared to the other types of angled roadside parking configurations, but vehicles need more room for manoeuvring. The following criteria apply to the design of the angled and perpendicular car parking stalls:

• For all types of intersections and all types of angled and perpendicular parking stalls, the distance shall be at least 12.0 m measured from the pedestrian crossing line and the first parking stall at the beginning of the roadway (according to the direction of traffic on the roadway) and at least 9.0 m from the stopping line and the last parking stall at the end of the roadway.

• For parking stalls at an angle of 45° to the direction of traffic, the minimum width of the roadway in one direction shall be 4.2 m, and the vertical dimension of the parking stall on the platform shall be 6.4 m. The minimum width of the roadway in two directions shall be 8.4 m. However, in case of land acquisition constraints, the width of one-directional and two-directional roadway shall be limited to 4.0 m and 8.0 m, respectively.

• For parking stalls at an angle of 60° to the direction of traffic, the minimum width of the roadway in one direction shall be 5.4 m, and the vertical dimension of the parking stall on the platform shall be 6.7 m. The minimum width of the roadway in two directions shall be 10.8 m. However, in case of land acquisition constraints, the width of one-directional and two-directional roadway shall be limited to 5.0 m and 10.0 m, respectively.

• For perpendicular parking stalls (at an angle of 90° to the direction of traffic), the minimum width of the roadway in one direction shall be 7.6 m, and the vertical dimension of the parking stall on the platform shall be 6.0 m. For a two-way roadway, the width shall be 15.2 m. However, in case of land acquisition constraints, the width of one-directional and two-directional roadway shall be limited to 6.0 m and 12.0 m, respectively.

• Parking stalls shall be appropriately marked

• In the event of acceleration or deceleration lanes, the distances are measured from the beginning of the tapered section to the last parking stall at the entrance to the intersection and from the end of the tapered section to the first parking place at the exit of the intersection.

• Oversizing of angled parking stalls should be avoided.

Surface Parking Facilities (Off-Street)

The surface parking facilities that are located outside the road right-of-way are termed as surface off-street parking facilities.

The division of a passenger car parking into series of parking spaces and aisles is determined by the desired traffic route, which in turn depends on the position of the entry and exit routes and the conditions for one-way and two-way aisle traffic.

When designing the movement of vehicles within the surface parking facility, the following should be taken into account:

• Traffic cycle should be short and safe and not confusing to the driver.

• All parking stalls should be clearly visible.

• Conflict points for the movement of vehicles should be eliminated to the extent possible.

• Aisles leading to the exit should be clear.

The following design criteria apply to surface parking:

• The minimum dimensions of an off-street perpendicular or angled parking stall shall be 6.0 m long and 3.0 m wide.

• The minimum dimensions of an off-street parallel parking stall shall be 6.50 m long and 2.5 m wide.

• The parking angle shall be chosen to give the highest possible number of parking spaces in accordance with the configuration and dimensions of the parking area. Angled parking stalls could be at angles of 30°, 45°, 60° or 90°. A uniform angled parking configuration shall generally be selected.

• Most efficient use of land area in larger parking stalls is obtained by placing all vehicles perpendicular to the aisles. In general, a perpendicular layout is readily adaptable and is desirable.

• Trees or other shading equipment (e.g., canopies) shall be installed in parking areas to provide shade, windbreaks, spatial enclosure, and a visual buffer of parking areas.

• 5% of surface parking spaces shall be allocated to people with disabilities, provided that the number of parking spaces is not less than two.

Parking Garages

Parking garages include in general simple structures or complex, multi-level garage parking facilities. The location of the parking structure shall be away from intersections and away from congested points in the road network. Space requirements for all features and installations related to parking garage structures must be taken into account in the early stage of the design, as they restrict the usable area and can also significantly impair the operation of the overall system.

The basic design components, such as, parking stall dimensions, aisle widths and circulation used for off-street surface parking also apply to parking structures.

Additional design requirements applicable to garage parking structures include the following:

• The various levels (excluding ramps) must be horizontal.

• The number of levels should preferably be limited to a maximum of six.

• The inner distance between the structure’s pillars shall not be less than 9.0 m, as wide as to accommodate three parking stalls.

• Each level shall have a minimum vertical clearance of 2.5 m.

• The height of the ground floor shall be preferably 3.75 m to allow entry of elevated vehicles.

• Counterclockwise rotation shall be preferred to match the entrance and exit traffic movement in the parking facility.

• 5 % of multi-floor parking spaces shall be allocated to parking spaces for people with disabilities.

Multi-level structures

Multi-level car parking structures are used where parking is in high demand, such as in cases of commercial complexes and mixed-use structures. There are two types of multi-level parking facilities. The first is the one that makes use of ramps, while the second type uses mechanical movement (car lifts). It is not advisable to use the second type (mechanical movement), because any malfunction often leads to the complete disruption of the facility.

Vehicles move from one level to another within the garage parking facility building via ramps. There are several different types of ramp systems and related structures with no single combination that can best fit-all. The selection should be made based on site layout and parking demand characteristics.

The following main four ramp systems are available:

• Full ramps, which connect levels in a tangent run. The ramps themselves are easy to drive on. However, the shifting of the ramps may have an unfavourable effect on the safety and quality of traffic flow.

• Semi-ramps, which connect the parking levels split in two parts and spaced half a level apart. The shorter ramps result to higher grades.

• Helical ramps, which are external ramps of the parking structures. Given the higher area requirements, helical ramps are particularly suitable for large park structures.

• Parking ramps, which form an integral part of the parking areas, as at least one side of the ramp is used also for parking. In cases where accessible parking spaces are provided, their grade shall not exceed 8 %. Parking ramps are the most economical solution; however, they are not suitable when shopping carts are used in the parking facility.

All the above ramp configurations may accommodate one-way or dual-way traffic; however, in semi-ramps, the widening of the lanes in curves may be required. The latter is usually difficult to accommodate. In any case, a swept path analysis shall be carried out.

In the case of dual-way ramps, care should be taken to ensure that there is as little as possible overlap of up-stream and down-stream traffic at their endings. Nevertheless, this can hardly be avoided in the case of helical ramps, which explains why they are less suitable in large installations with high degree of handling than, for example, helical ramps with one-way traffic.

In general, dual-way traffic as left-hand traffic shall be excluded for safety reasons. If it cannot be avoided in individual cases, e. g. the case of semi - ramp systems in left - hand corners and separate traffic streams, the individual lanes shall be clearly identified and separated by appropriate structural measures and vertical control devices.

Ramps are designed with safety clearances on both sides, which are raised to 0.08 m. On dual-way traffic ramps, safety clearance (raised by 0.08 m) is also designed between the opposing traffic.

The circulation path shall be free from physical and visual obstacles. Vehicle paths shall be designed respecting pedestrian conflicts.

Parking for the Disabled (Accessible Parking)

Parking spaces designated for individuals with disabilities or the mobility-impaired must be provided at all types of parking facilities.

As a general rule, 5 % of any parking space (parking garage or off-street surface parking facility) shall be allocated to parking stalls for people with disabilities. In more detail, the minimum number of parking space requirement is based on the total number of parking spaces in a facility.

The following design principles shall apply:

• Minimum stall dimensions shall be 6.0 m (length) x 3.5 m (width) including: an additional width of at least 1.6 m along each side, in cases of stalls perpendicular to the parking aisle; in cases of adjacent disabled parking stalls, space can be saved by using the same 1.6 m access aisle to serve both sides.

• Parking spaces for people with disabilities must be distinguished via appropriate signage, typically the international symbols of accessibility. It shall be clearly visible at the entrance to the parking area, and also when a vehicle is parked in the designated space.

• Parking spaces shall be located on level terrain with surface slopes that do not exceed 2% in all directions.

• In parking structures, parking stalls shall be located on the shortest possible accessible route to an accessible building entrance/elevator.

• Accessible parking stalls not located adjacent to the accessible entrances shall have signage that indicates the direction to these entrances.

• Sidewalks shall be equipped with the necessary well-lit ramps to reach the parking stalls with a width of not less than 0.9 m.

• Dropped curbs shall be provided adjacent to the parking stall to enable ease of access.

On-street parallel parking should only be provided to vehicles transporting disabled passengers who are able to board/alight on the passenger side. On-street parallel accessible parking stalls for vehicles must meet the following requirements:

• Minimum dimensions of 6.5 m x 2.5 m.

• Access aisle minimum dimensions 6.5 m x 2.4 m.

• Adequate vertical and horizontal clearance (minimum 2.5 m high and minimum 4.0 m wide to accommodate both parking space and access aisle).

Safety and Security Requirements

A number of measures shall be adopted to ensure the adequate safety and security of both the users and the parking facility.

With regard to entrances and exits, the following shall apply:

• Each entrance and exit shall be provided with an illuminated sign clearly indicating the “entrance” or “exit” in full.

• Each entrance shall be provided with a sign indicating the permissible vehicle height for entry. Movement of the sign plate shall be enabled if it comes into contact with the top of a vehicle exceeding the permissible height.

• Mobile barriers shall be placed at entrances and exits.

• Special consideration to the design of pedestrian paths shall be given in order, to ensure that the sidewalk level does not rise or fall in front of the entrances or exits in a way that impedes the movement of pedestrians or people with disabilities.

• Pavements leading to entrances or exits shall be marked in a clear colour to ensure the safety of pedestrians crossing.

Regarding internal circulation:

• Adequate sight lines shall be provided to enhance safety at points where traffic movement and flows conflict, such as, exit points from ramps and in between floors.

• Good visibility at locations where pedestrian access routes cross or intersect with vehicle circulation routes.

• Depending on the mode of use, escape routes and emergency crossings shall be provided in enclosed car parks, which are clearly identifiable even in the event of a power failure.

With regard to ramps:

• Skid resistant surface shall be provided on ramps.

• Additional anti-skid features that also limit vehicle speed on ramps include anti-skid bumps that shall be used on the floor of the entrance and exit ramps. These are either concrete humps within the ramp or metal strips fixed to the ramp.

• Skid resistant walkways shall be provided for pedestrians.

Regarding fire protection:

• Each floor shall be provided with the necessary extinguishing devices complementing the automatic fire extinguishing system when needed.

• Coordination shall be made with the local fire department of each individual site.

With regard to security, the following requirements shall apply:

• Surveillance, either through on-site personnel or CCTV cameras shall be provided in off-street parking facilities.

• On-site personnel shall be present especially in multi-level parking facilities.

• Landscaping and boundary features shall not obstruct surveillance or provide opportunities for concealment.

• High levels of illumination shall be provided throughout the facility with vandal resistant fixtures.

• Payment machines shall be positioned in high visibility, busy areas.

• Pillars shall preferably be spaced as far away as possible to allow more visibility and reduce the chances of hiding and stalking.

• As far as possible, elevators and stairs (stairs) should be visible through open walls.

• Escalators, where possible, should be preferred as an alternative to stairs and elevators, as they allow vertical movement between floors with a high degree of visibility.