Why are the typical low-slop roofs surfaces not appropriate when public access in planned?

Typical low slope roofs simply wont and are not rated for foot traffic. Check out hydrostop system they are very versatile and they have a system(coating that will hold up to foot traffic. However, the base should be able to hold up foot traffic, and a lot of of low slope surfaces are a foam system and that is not an acceptable base to handle foot traffic. Finally if you are thinking of making a low slope roof accessible to foot traffic you should have a qualified contractor and most likely an engineer take a look to determine if its safe.