Design of Off-Street Facilities

The following excerpts were taken from the1992 edition of the Traffic Engineering Handbook, published by the Institute of Transportation Engineers (pp. 205-215).

Elements of Good Design (pp. 205-206)

In designing any off-street parking facility, the elements of customer service, convenience, and safety with minimum interference to street traffic flow must receive high priority. Drivers desire to park their vehicles as close to their destination as possible. The accessibility, ease of entering, circulating, parking, unparking, and exiting are important factors. Good dimensions and internal circulation are more important than a few additional spaces. Better sight distances, maneuverability, traffic flow, parking ease, and circulation are the results of well-organized, adequately designed lot or garage.

Site Characteristics

Factors such as site dimensions, topography, and adjacent street profiles affect the design of off-street parking facilities. The relation of the site to the surrounding street system will affect the location of entry and exit points and the internal circulation pattern.

Access Location

External factors such as traffic controls and volumes on adjacent streets must be considered --- particularly the location of driveways or garage ramps. It is desirable to avoid locating access or egress points where vehicles entering or leaving the site would conflict with large numbers of pedestrians. Similarly, street traffic volumes, turning restrictions, and one-way postings may limit points at which entrances and exits can logically be placed. It is important to investigate these factors at the beginning of design.

Driveways should be located to provide maximum storage space and distance form controlled intersections. . . .

General Elements and Layout Alternatives (p. 212)

Because of their lack of walls or cover, parking lots have no ventilation problems, and lighting is sometimes provided by relatively tall poles, thus affording high efficiencies and minimizing the number of poles. Generally, lots have clear sight lines and offer a feeling of greater security than in a more confined space. Lots are not restricted on vehicle heights and thus afford access to both commercial and emergency vehicles. . . .

Generally, the layout of a parking lot seeks to strike a balance among maximizing capacity, maneuverability, and circulation. . . .

The general advantages of 90° parking, as compared with lesser angles, are:

1. Most common and understandable;
2. Can sometimes be better fitted into buildings;
3. Generally most efficient if site is sufficiently large;
4. Uses two-way movement (can allow short, dead-end aisles);
5. Allows unparking in either direction. Thus it can minimize travel distances and internal conflict;
6. Does not require any aisle directional signs or markings;
7. Wide aisles often provide room to pass vehicles stopped and waiting for an unparking vehicle;
8. Wide aisles increase separation for pedestrians walking in the aisle and between moving vehicles;
9. Wide aisles increase clearance from other traffic in the aisle, during unparking maneuvers;
10. Fewer total aisles (hence easier to locate parked vehicle).

Several advantages and disadvantages of angle parking (usually 45° to 75° ), are:

1. Easiest in which to park
2. Can be adapted to almost any width of site by varying the angle;
3. Requires slightly deeper stalls but much narrower aisles and modules;
4. Drivers must unpark and proceed in original direction; hence producing greater out-of-way travel and conflict;
5. Unused triangles at end of parking aisles reduce overall efficiency;
6. To avoid long travel, additional cross aisles for one-way travel are required, which adds to gross area used per car parked;
7. Difficult to sign one-way aisles.

Wheel Stops and Speed Bumps (p. 215)

In general, the ends of parking stalls within lots can be marked in a satisfactory fashion by only a paint line. Wheel stop blocks in the interior of a lot have disadvantages, for they may interfere with and present a hazard to people walking between cars, provide traps for blowing debris, and interfere with snow plowing in northern climates. . . .

Wheel stops are often used along the side boundaries of a lot, where large landscaped areas extend beyond the edge of pavement and an occasional override would present no significant hazard.