Hm I just found a website saying:

Utah’s basic speed law and the presumed speed limit

Maximum speed limits in Utah are the direct statutory consequence of Utah’s Basic Speed Law which states:
A person may not operate a vehicle at a speed greater than is reasonable and prudent under the existing conditions, giving regard to the actual and potential hazards then existing.
UT ST §41-6a-601(1)

What makes Utah’s maximum speed limits unique is that exceeding them results in merely a presumption, not a determination, of a violation of the Utah Basic Speed Law. Most other states have strict liability speed limits, whereby a ticket for speeding is based solely upon the prima facia (latin for at first face or appearance) evidence that you were physically exceeding the posted limit. This evidence is obtained by local or state police or county sheriff using radar or pacing.

In most states other than Utah merely exceeding the speed limit, albeit safely, reasonably and prudently, given the present road, weather and traffic conditions, cannot be raised as a valid defense in traffic court. In Utah this defense can be validly raised. In other words, even if you are caught exceeding the speed limit, Utah allows you to claim your innocence if you can present affirmative evidence that you did so safely and in conformance with the letter and spirit of the Basic Speed Law (which does not actually make any explicit reference to maximum speed limits).


But maybe the information is incorrect