If the existing accessible parking spaces are in compliance with the 1991 ADA Standards, then the “safe harbor” provision applies and you do not have to make modifications to the accessible parking spaces even though the new 2010 ADA Standards have a few different requirements. However, if your business chooses to alter the parking spaces, the safe harbor no longer applies and your accessible parking must comply with the 2010 ADA Standards.
For example: A business’ parking lot has a total of 250 parking spaces and, as required in the 1991 Standards, the lot includes seven accessible parking spaces, one of which is van-accessible. The 2010 Standards now require two van-accessible spaces even though the total minimum number of accessible spaces remains at seven. The business does not have to modify its parking lot to provide the additional van-accessible space until the lot undergoes a planned alteration (re-striping, re-surfacing, etc.).
If the existing accessible parking spaces are not in compliance with the 1991 ADA Standards, you must construct or alter accessible parking spaces in compliance with the 2010 ADA Standards if it is readily achievable to do so.