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.
While towing a trailer on a highway with a 65 mph speed limit, you should adhere to that limit if it is safe to do so. Make sure your vehicle and trailer are properly equipped and balanced, and maintain a safe following distance from other vehicles. Drive at a speed that is comfortable and manageable given the conditions.
55
45 mph
"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
The speed limit on most freeways in California is 65 miles per hour, but it can vary in certain areas.
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.