Currently, all the states of our country adopted the laws, which set up speed limitations on the roads and highways. Speed limit is maximum (or minimum) speed established by legislation for one of another type of road. Usually, the drivers can be informed about speed limits on the roads with the help of traffic signs, which appear next to the roads.

Of course, speed limits vary according to the type of the roads and type of the vehicle. A number of states have different speed limits for such vehicles, as buses, trucks and other commercial means of transportation and, as a rule, maximum speed limit for such vehicles is lower, than the one for usual cars. Also, some states have different day-time speed limitations and night-time speed limitations.

Average speed limits in the United States are the following: 45–70 mph on the highways and expressways, connecting the cities or towns, 55–70 mph on non-Interstate expressways, and up to75 mph on interstate freeways. In some states speed limits can exceed 75 mph, like in Texas or Kansas, where it is allowed to drive with the speed 80mph on some roads. Certainly, speed limits slightly vary from one state to another. For example, in Arizona usual maximum speed limit for highways is 75 mph, and in Tennessee it is at most 65 mph. It is interesting also, that generally the states on the West of the country have speed higher limits, than the ones in the East.

There is a special rule, connected with establishing of speed limits, which is used in our country since the middle of XX century. It is called the 85th Percentile Rule. The concept of this rule is the following: typically 85% of drivers do not exceed the threshold of safeness in normal circumstances. It means that 85% of drivers usually drive with the speed, which is relatively safe for particular road or highway. That is why the majority of current speed limitations are set by traffic engineers, according to this finding.