ADAAG 4.7.2 Slope.
Slopes of curb ramps shall comply with 4.8.2. […] Transitions from ramps to walks,
gutters, or streets shall be flush and free of abrupt changes. Maximum slopes of
adjoining gutters, road surface immediately adjacent to the curb ramp, or accessible route
shall not exceed 1:20.
ADAAG 4.8.2 Slope and Rise.
The least possible slope shall be used for any ramp. The maximum slope of a ramp in
new construction shall be 1:12. [...] Curb ramps and ramps to be constructed on existing
sites [...] may have slopes and rises as allowed in 4.1.6(3)(a) if space limitations prohibit
the use of a 1:12 slope or less.