The ADAAG also requires that one of every 8 spaces be van accessible (with wider accesss aisle)
4.1.1(b) Explains that you need to consider the following factors when making your decisions:
a) population being served
b) availability to user
c) location relative to distance and time
d) location relative to isolation and separation
e)function of the building or facility
f) equal treatment and opportunity
So this means that if you know more or less where your front doors will be located, then we need to try to locate the parking spaces in a logical place on the site close to the front doors, and in the same path of travel as the rest of the population. This may be just our best guesses sometimes.
Remember that the minimum number of accessible spaces is determined by the number of spaces in your parking lot, not your occupant load. Therefore it is also important to know where your parking lots are in relation to your buildings. If there is a parking lot along the perimeter of the site, but it is not close to a building, then the likelihood of needing an accessible space there is not very great.
On the other hand, if you have a parking lot close to your building, then count the spaces of that lot, and locate your accessible spaces so they are the shortest distance possible. Sometimes you might have to have more than the minimum in order to achieve the intended result of getting the spaces as close as possible to the entrances. Keep in mind that the users are not able to travel very far using their wheel chair.
If you want more information, the Access Board will have a FREE Webinar on May 6th, 2010 about Parking and Passenger Loading Zones