Approach and Departure Angle Design for Fire Trucks

[CFCivil]

The local fire department has established a standard that sets the maximum approach/departure angle at 10.5%. I understand this to mean that I can not have an instantanious grade change of more than 10.5%. Lets say I need to transition between 2% and 15% grade at a residential driveway. I will no doubt need a vertical curve of some length. It is the determination of that length that I am wanting help with. It would seem that the mimimum limit of the VC length would be equal to a distance greater than the wheelbase of the longest wheelbase fire engine that the department would expect to fight a residential structure fire with. If the wheelbase were to be assumed to be 30', then a fire truck "centered" on a vertical curve g1=2% g2=15% with a VC length of 30'would be at a grade of (15-2)/2 = 6.5%. If the max rate of grade change of a VC is at the Midpoint of the VC then that would be the "worst case". 15%-6.5% = 8.5% comfortably under the 10.5%.

Does any of this hold water? Sorry for being so long winded?

Thanks for your thoughts,
CFCivil