AUSTIN, Texas — The new US 183 South toll road runs from U.S. 290 East to Texas 71 near the Austin airport. The 8-mile roadway opened in early 2021 but, more than a year later, it still has no posted speed limits.
However, that doesn't mean drivers can drive as fast as they want.
In Texas, most highways have a default speed limit of 70 mph unless there is some hazard that requires motorists to drive slower. However, speed limits can be more or less than 70 miles an hour.
According to a report from KUT, for the past year, the Central Texas Regional Mobility Authority (CTRMA) has been conducting a study to figure out what the posted speed limit should be on US 183 South.
Mike Sexton, the CTRMA's acting director of engineering, told KUT that the agency hired a firm to go out to the road during off-peak periods when traffic is moving freely. The crews set out devices that collect the speeds of vehicles and that data is then run through an analysis.
That analysis then determines something called the 85th percentile speed, which is the speed at which 85% of cars are traveling at or below. To put it another way, KUT said if you had 100 cars driving down the road, the 15th fastest car would be the speed the CTRMA is looking for.
"That's determined to be the most safe and prudent speed for the corridor," Sexton told KUT. "That's the speed that you drive feeling safe on the roadways, and generally the rest of the vehicles around you are kind of doing that same speed."
The 85th percentile speed method is outlined in a Texas Department of Transportation manual and is used for highways all over the state.
KUT reports that the yearlong speed limit study for US 183 South is complete, but the CTRMA would not reveal what speeds the study recommended. However, Central Texans will learn the answer soon.
The CTRMA's board of directors voted on the recommended speed limit on Monday, April 25. They decided on 75 mph. Speed limit signs can now be posted.
To learn more about Texas' process of deciding speed limits and how the state enforces those limits, read KUT's full report.
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