SH-99 Grand Parkway from US-290 to I-45 is now open. No tolls on this segment of SH-99 until February 15.
The Greater Houston Transportation and Emergency Management Center City of Houston Harris County METRO Texas Department of Transportation
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Houston TranStar AVI Traffic Monitoring System

Introduction | AVI Technology  | How It Works

How It Works

The system uses vehicles equipped with transponder tags as vehicle probes. The main source of vehicle probes are commuters using the "EZ-Tag" automatic toll collection system installed by the Harris County Toll Road Authority (HCTRA). Transponder tag readers are placed at 1 to 5 mile intervals along freeways and HOV lanes. Each reader senses probe vehicles as they pass a reader station and transmits the time and location of the probes to a central computer over a telephone line. As the probe vehicles pass through successive AVI readers, software calculates average travel times and speeds for a roadway segment. The averages are made available to software which provides the data for the Houston TranStar web site.

See an animated demonstration of the system.