<P> Speed limits in the United States vary depending on jurisdiction, with 75 to 80 mph (120 to 130 km / h) common in the Western United States and 65 to 75 mph (100 to 120 km / h) common in the Eastern United States . States may also set special speed limits for trucks and night travel along with minimum speed limits . The highest speed limit in the country is 85 mph (140 km / h), which is posted on a single stretch of tollway in rural Texas . </P> <P> In Alabama, it is illegal to drive at a speed that is not "reasonable and prudent" for the current conditions and hazards . Drivers must also not drive so slowly that they impede the flow of traffic . If the speed limit is not otherwise posted, it is: </P>

The speed limit on some interstate highways is roughly 135 km/h