Counting Cars: How TxDOT keeps track of traffic volume

The traffic volumes the cables read will be used for future design. (Dugan/KXAN)
The traffic volumes the cables read will be used for future design. (Dugan/KXAN)

AUSTIN (KXAN) — The Texas Department of Transportation annually collects on average 82,000 short-term traffic counts, 1,000 manual traffic counts and more than 300 long-term counts. Data is collected 24 hours a day, 365 days a year to support federal, state, regional and local transportation entities.

The traffic counters are long black cables that are strewn across a road, usually in a set of three. They’re screwed right into the pavement but many times fast moving traffic can rip the cables right out of the road.

TxDOT spokesperson Diann Hodges says staying on top of ever changing traffic data is crucial for future road development. “To account for how much traffic we’re going to have on the interstate as we transform 79 miles of I-35 we want to get a true understanding of just how much traffic is on the road.”

Along with counting cars annually, TxDOT also monitors traffic entering and exiting highways and through traffic every five years. “It gives us the most information possible for us to make the best decisions for improvements to the road,” says Hodges.

Twenty-four hour counts are currently underway from Farm to Market 1431 in Williamson County to State Highway 45 SE in Hays County. Along with counts on entrance and exit ramps, they’re also studying four major locations on Interstate 35 main lanes and frontage roads with radar.

  • I-35 and 51st Street
  • I-35 near Stassney Lane
  • I-35 near SH 45N
  • I-35 near FM 1431

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