Limestone sand/aggregate may not be your best paving choice
QUESTION: I eagerly read your monthly column and have a follow-up question about ground surface treatments. We have a rail/trail with the portion outside of city limits made of a finely compacted limestone sand. This surface, over time, becomes very stable and solid due to the cementitious characteristics of the limestone. Folks using wheelchairs and parents with strollers use this trail often. My question is related to the gravel parking lot’s accessible parking spaces and accessible route to the rail/trail surface. Since funds are limited, we are hoping that the compacted limestone sand now used on the actual rail/trail is acceptable for the parking lot. Can you help us out? -Terry
Answer: In my area we call it limestone aggregate, and I’m sure it has other titles in other areas. No matter what you call it, it is addressed by Surfaces 302.1 General in the 2010 ADA Accessibility Guidelines (ADAAG), which states that floor and ground surfaces shall be stable, firm, and slip-resistant. In particular, the Advisory for 302.1 states:
“A firm surface resists deformation by either indentations or particles moving on its surface. A slip-resistant surface provides sufficient frictional counterforce to the forces exerted in walking to permit safe ambulation. “
My personal experience is that rain, wind, and usage causes eventual corrosion with ruts and washed-off edges, resulting in the “deformation by either indentations or particles moving on its surface.” Knowing about this problem, my concern is that the constant maintenance efforts required to prevent the corrosion and deformation might end up costing more in the end. A question that you need to ask is whether the up-front cost of asphalt or concrete would actually save money over the long run.
By the way, I love trails with asphalt rather than concrete. They provide a softer surface for runners and walkers. Asphalt also blends better with trail aesthetics. Some jurisdictions even color the asphalt to match the surrounding vegetation.
You also mentioned that the surface, over time, becomes very stable and solid. But what happens while the surface is in the process of becoming stable and solid? That is another problem.
Concerning the actual parking space and access aisle: These positions must be identified with appropriate marking, as specified in 502.3.3 Marking (“Access aisles shall be marked so as to discourage parking in them.” See Figure 502.3 Parking space access aisle.) Now, according to the Advisory for 502.3.3:
“The method and color of marking are not specified by these requirements but may be addressed by state or local laws or regulations. Because these requirements permit the van access aisle to be as wide as a parking space, it is important that the aisle be clearly marked.” (See Figure 502.2 Vehicle parking spaces)
Can you provide the required marking for the spaces and access aisle using the limestone sand? Also, don’t forget the requirement that the slope in all directions of an accessible parking space and access aisle cannot be steeper than 1:48.
Cross slopes and other concerns
Below are a few more 2010 ADAAG regulations that you should consider.
502.4 Floor or Ground Surfaces. Parking spaces and access aisles serving them shall comply with 302. Access aisles shall be at the same level as the parking spaces they serve. Changes in level are not permitted.
EXCEPTION: Slopes not steeper than 1:48 shall be permitted.
Advisory 502.4 Floor or Ground Surfaces. Access aisles are required to be nearly level in all directions to provide a surface for wheelchair transfer to and from vehicles. The exception allows sufficient slope for drainage. Built-up curb ramps are not permitted to project into access aisles and parking spaces because they would create slopes greater than 1:48.
502.6 Identification. Parking space identification signs shall include the International Symbol of Accessibility complying with 703.7.2.1. Signs identifying van parking spaces shall contain the designation “van accessible.” Signs shall be 60 inches (1525 mm) minimum above the finish floor or ground surface measured to the bottom of the sign.
502.7 Relationship to Accessible Routes. Parking spaces and access aisles shall be designed so that cars and vans, when parked, cannot obstruct the required clear width of adjacent accessible routes.
Advisory 502.3.4 Location. Wheelchair lifts typically are installed on the passenger side of vans. Many drivers, especially those who operate vans, find it more difficult to back into parking spaces than to back out into comparatively unrestricted vehicular lanes. For this reason, where a van and car share an access aisle, consider locating the van space so that the access aisle is on the passenger side of the van space.
You should also check out your state and local county or city regulations. They are permitted as long as they are more stringent than the federal requirements.
I can’t make the decision for you. But I hope the concerns I have shared, along with the actual regulations, will help you with your final decision.