Park-and-Ride Lot Calculator

Total Parking Spaces is sized purely from how many riders are expected to drive and park (Daily Station Ridership, Drive-to-Station percentage, and Avg Vehicle Occupancy). ADA Spaces (%) is applied afterward, carving a percentage of that already-calculated total out as ADA-accessible rather than adding extra spaces on top, so it has no effect on the overall lot size.

Avg Vehicle Occupancy represents how many riders typically share a single car, so it divides the number of car-driving riders down to a number of vehicles. Raising Avg Vehicle Occupancy (more carpooling) reduces Total Parking Spaces for the same ridership, since fewer individual cars are needed to move the same number of people.

The 325 square feet figure is a standard planning allowance that covers not just the parking stall itself but also a share of the drive aisles and circulation space needed to access it, following typical Institute of Transportation Engineers (ITE) planning guidance. That is why Lot Area scales up directly with Total Parking Spaces rather than just the stall footprint alone.

Total Parking Spaces scales linearly with Daily Station Ridership when the Drive-to-Station percentage and Avg Vehicle Occupancy stay fixed, so doubling ridership roughly doubles the number of spaces needed. Since Lot Area is a fixed multiple of Total Parking Spaces, it grows by about the same proportion.

It is floored at the federal minimum. The 2010 ADA Standards for Accessible Design set accessible-space counts with a table (Section 208.2), not a flat percentage: 1 accessible space for lots of 1-25 spaces, 2 for 26-50, 4 for 76-100, 5 for 101-150, and so on up to 2% of the total for 501-1,000 spaces. This calculator takes whichever is larger -- your entered ADA Spaces (%) or that statutory minimum -- and also reports the minimum separately as ADA Minimum Required. One of every six accessible spaces must additionally be van-accessible, which this calculator does not break out.