By John McDevitt

John McDevitt

PHILADELPHIA (CBS) – Planning a summer road trip? Watch your speed because how fast you can go varies from state to state.

Thirty-six states have speed limits of 70 mph or above on some roads, according to the Insurance Institute for Highway Safety.

The highest in the nation is in Texas with an 85 mph limit on a 40-mile stretch of divided toll highway between Austin and San Antonio.

In Pennsylvania and New Jersey the highest posted sign is 65 mph.

“We believe that speed limits have to be set in a way that improves mobility, safety and respect for the law, so it’s really an individual thing about the location,” says Jenny Robinson, with AAA Mid Atlantic. “We urge states to use engineering studies [and] traffic studies to figure out what that safe best maximum speed limit should be for that particular roadway.”

Robinson says higher speeds present safety issues in terms of potential crashes and more gas is used when traveling more than 65 mph.