:h
Not sure if this has been previously mentioned, but good grief! How many times in ones actual towing are you going from zero to sixty????
I'd say not that many times.
Most are mentioning merging into freeway traffic from an on ramp. Yes, many of these begin just after stop lights, but a turn is usually involved and once one hits the actual ramp from the light itself, you have some sort of rolling speed going that you actually accelerate from.
So I would guess that the acceleration involved comes once one has built up a little rolling speed, in the 20 MPH range or better, and one goes up from there.
In my mind (warped as it is :B ) it is this acceleration, from an already moving vehicle, that is of the most importance.
Zero and up is irrelevant. It is what the vehicle does merging, passing or whatever, and that acceleration starts from an already moving vehicle.