The same as it is for any other vehicle.
Know that most all trailer tires, with an "ST" before the tire size, are rated for max. 65 MPH. While you won't get a speeding ticket for going 70 on a freeway driving a vehicle towing a trailer ... you are risking tire failure.
45 mph
55
"The maximum speed limit on the freeway is 70mph."
The highest speed limit I know of on an Interstate highway in the U.S. is 75 MPH, but that varies.
60 Maximum Speed Towing a Trailer (in the UK)
the answer is 30mph
70 mph. But the turnpikes are 75 mph.
5 mph
Germany has the Autobahn there is no speed limit on the Autobahn. It is Germany's version of a freeway.
90 Km/Hr
Varies by jurisdiction. In Texas, these roads have speed limits of up to 75 MPH.