Fastest, slowest states: Where your state ranks

This year marks four decades since President Richard M. Nixon signed into law a mandate that set the maximum national speed limit at 55 mph, helping to fend off an oil crisis, diminishing Americans' ability to make good time on a cross-country road trip and inspiring rocker Sammy Hagar's signature song. It's been nearly two decades since that law's repeal and, since then, two-thirds of U.S. states have picked up the pace significantly, raising their speed limits to 70 mph or higher on stretches of their roadways.

So which state is the fastest? Put another way, which states have the highest average top speed limit?

Well, if you're familiar with the saying, "everything's bigger in Texas," the sentiment extends to speed limits, too. The Lone Star State not only lays claim to the fastest posted limit on a single highway in the U.S., it also boasts the greatest overall top speed when you average the highest allowable speeds on its rural interstates, urban interstates and other limited access roads, as compiled by the Governors Highway Safety Association.

That nonprofit group, which represents the nation's state and territorial highway safety offices, lists Texas' 85 mph speed limit as the highest in the U.S. Moreover, the state's average top speed for all three types of roadways is 78.3. That's nearly 2 mph greater than the next-fastest state, Idaho, which has a top limit of 80 mph and an average top speed of 76.7 mph.

On the other end of the speed spectrum are Alaska and the District of Columbia, both of which have a top speed and average top speed of 55 mph, according to the GHSA.

As Cars.com previously reported, the high-speed portion of Texas State Highway 130, which stretches 91 miles between San Antonio and Austin, became the nation's first 85-mph toll road in late 2012. Also, as of late July, Idaho raised speed limits to 80 mph on stretches of several interstates. The Gem State's transportation department initially put the brakes on the speed hike, following lawmakers' authorization of the increase, so that it could complete safety studies at the urging of the AAA of Idaho. Those studies, according to Idaho's KTVB-TV news, have been completed, and crews began replacing speed-limit signs July 24.

Safety advocates generally don't view raising speed limits in a favorable light. At the time Texas debuted its 85 mph speed limit, Insurance Institute for Highway Safety spokesman Russ Rader said in a statement that, "the research is clear that when speed limits go up, fatalities go up." That said, the 55 mph national limit wasn't set for safety's sake, but in an effort to conserve fuel on a national level during the 1973 oil crisis, when gas prices quadrupled.

Since that time, we as a nation have hit the gas. Four states — Idaho, Texas, Utah and Wyoming — now have top authorized limits of at least 80 mph. A dozen more states have top speed limits of 75 mph, including Kansas, Louisiana, Maine, Montana, Nevada, New Mexico, North Dakota, Oklahoma and South Dakota. Moreover, 22 additional states have a top speed limit of 70 mph, five of which (Michigan, Mississippi, North Carolina, Pennsylvania and Tennessee) average 70 mph across their urban and rural interstates and other limited-access roads, as listed by the GHSA.

In addition to the aforementioned pokiest places of Alaska and the District of Columbia and their 55 mph limits, five more states — Delaware, Hawaii, New York, Rhode Island and Vermont — all have top speeds of no more than 65 mph and average top speeds in just the high-50s.

See how your state ranks in the chart above.