Maximum Slope for Heavy-Duty Vehicle Parking Lot

What is the maximum grade/gradient allowed for non-temporary (overnight or longer) parking/vehicle storage areas in parking lots for heavy-duty vehicles such as semi-trucks and buses?

All I could find is that the International Building Code allows a maximum gradient of 1:15 (6 2/3% grade) in any direction for parking spots, that the Americans with Disabilities Act allows 1:20 (5%) running/longitudinal maximum for accessible areas that do not count as ramps, and that the ADA allows a maximum of 1:48 (2.0833%), with 1:50 (2%) preferred maximum, in any direction for disabled parking spots.

On a related note, I could also find that the Federal Aviation Administration limits the runway to 1.5% longitudinal maximum for aircraft approach categories C, D, and E (all jet airliners (heavy-duty if such a classification existed) fall within this), that the FAA limits it to 0.8% maximum longitudinal for the first and last quarters of the runway for the same categories, and that the FAA limits airport aprons (parking areas) to 1% maximum in any direction for the same categories.

Similarly, I could find that most mainline railroads (more accurately railways) and metros limit it to 0.5%-1% maximum at station platforms, most mainlines 0.1%-0.25% maximum in parking and coupling/decoupling areas, most metros 0.15%-0.5% maximum in parking and coupling/decoupling areas, most light rails 1%-2% at station platforms, and most light rails 0.3%-0.5% in parking and coupling/decoupling areas.

So, is there any legal, industry, or trade association standard that sets a maximum slope for truck and bus long-term parking/vehicle storage areas, especially to prevent rollaways in case of brake failures? Here, I am not referring to loading docks, where there is a structure to rest against.