When Texas first increased their speed limits to 80 on long stretches, they dropped them down to 65 at night.

My girlfriend and I just finished a road trip through thirteen states with nearly as many speed limit schemes. And in all of them, fifty-five as a standard limit on the highway is pretty much dead. Most states appear to go at least as high as seventy. That’s good. The 55 limit was rarely observed unless a cop was nearby or your grandma was at the wheel, and often not even then, and it made our roads more dangerous.

One other thing I noticed, however, is that throughout most of our trip the highway speed limit that garnered the most compliance was 70 mpg. Where the speed limit was 55, people drove 65 to 80. Where the speed limit was 65¹, people drove 65-75. Where the speed limit was 70, people drove 68-75.

Except in Texas, where 75 means people drive 70-75. Eighty means 70-80, and 65 means 60-70. I expect this is because we assume that, since speed limits are set to 80² when appropriate, the 75, 70, and 65 limits are also appropriate rather than arbitrary.

Even the rare 55 zones get higher compliance in Texas, in my experience, than in other states. When we hit New York, I instinctively dropped to 55-60 when we hit a 55 mph highway, until I started getting almost rear-ended by New Yorkers going 75-80. I slowed down because my experience in Texas is that the safe speed limit is usually near the posted speed limit. I was quickly disabused of that notion while driving from Chatham to Ithaca.

Texas’s speed limits make it a lot easier for us Californians to come to the Lone Star State… quickly.

Research backs up my personal experience over the last several weeks: drivers do not automatically drive over the speed limit by the same amount when speed limits are increased; drivers tend to drive the safe speed for the road and conditions, and continue doing so when the speed limit changes, whether up or down. The main effect of a speed limit increase is to allow law enforcement to focus on those few drivers who do not drive safely.

We have the National Motorists Association to thank for fighting the inane 55 mile per hour national limit. They kept on congress and the states to pay attention to real-world research when most people thought 55 was here to stay. Without the NMA, our six-week road trip would have meant a lot more time on more dangerous roads and a lot less time enjoying our destinations!