I have been researching this issue for a while now and the requirements are both pretty specific and yet, in another way, very general. Essentially, a city is required to make all pedestrian crossing on streets accessible to those who are disabled/handicapped.
The ADA sets out minimal requirements and then states can deviate from those if they choose to do so but they are only allowed to deviate and provide more or better access, never less.
All of the requirements are set out in various codes but it is easier to look through and understand the publications based on those codes than it is to look through the codes themselves, most of which are either in the United States Codes or the Code of Federal regulations.
Note that any deviation from these rules in a manner that makes it harder for a disabled person to use the walkways can be addressed through a lawsuit.
To be honest, I've never been in the building trade other than as a laborer and so when they discuss that "The slope requirements for the flared sides depend on the width of the sidewalk at the top of the ramp, “x” in the illustration to the right. If “x” is less than 48 inches, then the slope of the flared sides must be no more than 8.33 percent (1:12). If “x” is 48 inches or more, then the flared sides may slope up to 10 percent (1:10) but not more", I am lost as to what they are talking about, other than that I understand they are talking about how steep the ramp can be.
I am going to give you the link to a couple of ADa publications put out by the government and which appear to be to be the regulations which you are concerned about. If you would look these over and then tell me which direction you would like for me to look next.
This next link discusses the temporary access to areas while the area is being worked on. Note that the last "check box" on the second page states:
Make pedestrian routes ADA compliant and available to pedestrians during all phases of construction.