The way speed limits go up and down on different stretches of the same Texas roads can be confusing. A law approved by lawmakers in Austin and sent to Governor Abbott for his signature could make it even worse.

The legislature has approved a law that would allow for variable speed limits.

That's right, the road you traveled yesterday with a speed limit of 75 could have a speed limit of 60 today. It could be 70 tomorrow. To many, it sounds like just another speed trap. Traffic engineers, however, say that is not so.

Variable speed limits or VSLs use available information on the roadway, like traffic speed, the number of vehicles, and road surface conditions to determine appropriate rates and display them to drivers in real-time.

According to the U.S. Department of Transportation Federal Highway Administration, VSLs improve driver expectations by providing information in advance of slowdowns and potential lane closures. This reduces the probability of secondary crashes. It can also slow down drivers when weather conditions make driving more hazardous, or visibilities are lowered.

Not everyone agrees, and pilot programs studying the effectiveness of variable speed limits are mixed. Sheila Dunn, a Wisconsin-based National Motorists Association spokeswoman, a drivers' rights group, said variable speed limits confuse drivers, and some consider them nothing more than a speed trap.

A federal study found that enforcement has been challenging for police. Officers are unsure of the speed limit or fear there isn't enough supporting evidence to issue speeding citations.

If police aren't even sure of the speed limits at any given time, how can motorists be expected to keep up?

Another problem is the systems are expensive. Deploying changeable lighted speed limit signs along a route can cost millions. Some suggest that money would be better spent on upgrading the roads themselves.

In Missouri, they walked away from variable speed limits. Tom Blair, a district engineer for the Missouri Department of Transportation, told a press conference, "We walked away from it because we couldn't prove we had dramatically reduced the number of crashes or decreased traffic congestion."

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Studies in Georgia and Wyoming found that variable speed limits did reduce accident rates. At the same time, studies in Virginia were inconclusive.

I guess we'll have to wait and see the impact in Texas. Governor Abbott is expected to sign the measure into law.

Being able to change the speed limit in real time makes me nervous. In a state that has more legal speed traps than any other, maybe I'm just skeptical that this is anything but another form of legalized highway robbery by law enforcement.

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