Here is a link to all 50 states maximum legal speed limit for towing a
boat. It also shows numerous other requirements for towing in all 50
states.

I am sure no one in here has ever exceeded the maximum legal speed limit
on our Interstates, so we don't even need to consider the thought that
anyone would ever exceed the legal speed.

http://www.hitchsafe.com/Hitch-Cover.html

Here is the maximum speed limits for cars in the US.

http://en.wikipedia.org/wiki/Speed_l..._United_States

You will notice that trucks in many states have a lower speed limit than
cars.

http://en.wikipedia.org/wiki/Speed_l..._differentials