Parking Studies and Layouts
Learn the fundamental principles of evaluating parking supply and demand, the geometry of parking stall layouts, and the operational characteristics of off-street and on-street facilities.
Parking Accumulation
The total number of vehicles parked in a specific area (a lot, a block, or an entire district) at any given moment in time.
Key Parking Metrics
Engineers use standard metrics to evaluate the efficiency and utilization of parking facilities.
Fundamental Parking Equations
- Parking Volume (): The total number of vehicles that parked in a study area during a specific period of time (e.g., 500 cars parked between 8 AM and 6 PM).
- Parking Load (): The total volume of parking expressed in space-hours. It is calculated by integrating the accumulation curve over time or multiplying the volume by the average duration. (e.g., ).
- Average Parking Duration (): The average length of time a vehicle remains parked. .
- Parking Turnover (): The rate of usage of a single parking space over a given period. It indicates how many different vehicles utilized one space. . High turnover (e.g., > 4) is desirable for retail areas to maximize customer access.
Parking Supply vs. Demand
- Practical Capacity: For operational efficiency, a parking facility should never operate at 100% occupancy. Planners generally consider a facility "full" at 85% to 90% occupancy. This allows arriving drivers to easily find the remaining empty spaces without excessive circulating and queuing, which would otherwise spill out onto the adjacent street network and cause congestion.
- Parking Generation: Similar to trip generation, this is the process of estimating the peak parking demand a new development will create based on its size and land use (e.g., 4 spaces per 1,000 sq ft of retail space).
Geometric Layouts and Efficiency
The geometric design of a parking lot dramatically affects how many cars it can hold and how safely drivers can maneuver.
On-Street Parking
Checklist
- Parallel Parking: The most common form of on-street parking. It requires the most linear curb length per vehicle (typically 20 to 22 feet per stall) but minimizes the width taken from the travel lane.
- Angle Parking: Increases the number of vehicles that can be parked along a given curb length but requires a wider road cross-section. It is easier for drivers to enter than parallel parking but creates safety hazards when backing out blindly into the travel lane.
Off-Street Parking (Lots and Garages)
Checklist
- 90-Degree (Perpendicular) Parking: Requires the widest parking aisles (typically 24 feet) to allow a vehicle to swing in and out fully. However, it is the most efficient use of total floor area per parked car and allows for two-way traffic in the aisles.
- Angle Parking (45, 60, or 75 Degrees): Easier for drivers to pull into and requires a narrower aisle width (e.g., 18 feet for 60-degree parking). However, it strictly requires one-way traffic circulation in the aisles, making the overall site layout less flexible.
- Stall Dimensions: Standard passenger car stalls are typically 9 feet wide by 18 feet deep (9x18). Compact car stalls (often 8x16) can be used to squeeze in more capacity, but overusing them leads to sideswipe damage and driver frustration.
Modern Parking Management
Strategies to handle excess demand without building expensive new structures.
Demand Management Strategies
- Dynamic Pricing: Automatically adjusting parking meter rates based on current occupancy. If a block is consistently 100% full, the price is raised until occupancy drops back to the target 85%, freeing up spaces for high-priority short-term parkers (like retail shoppers) and pushing long-term parkers (like employees) to cheaper, remote lots.
- Shared Parking: A concept where adjacent developments with different peak demand times share a single parking facility. For example, an office building (peaks at 10 AM on weekdays) sharing a garage with a movie theater (peaks at 8 PM on weekends), drastically reducing the total number of spaces that need to be constructed.
Key Takeaways
- Parking Turnover measures the number of different vehicles that use a single space during a study period; high turnover is critical for retail viability.
- 90-Degree parking is the most space-efficient layout overall and supports two-way aisles, though it requires the widest aisle width for maneuvering.
- Angle parking allows for narrower aisles and easier entry but restricts traffic to one-way circulation.
- An occupancy rate of 85% to 90% is considered the "practical capacity" of a facility to prevent excessive circulation delay.