Traffic Sensor Technologies
Houston TranStar uses various technologies to measure the average speed and travel time of vehicles as they travel along a roadway. Information collected from these technologies is the source for providing travelers with traffic information in various formats including:
- The color-coded speed map on the Houston TranStar Website.
- Travel time messages on roadside message signs.
- Information used by radio and television media for reporting traffic conditions.
Anonymous Wireless Address Matching (Bluetooth™)
Houston TranStar's AWAM System detects vehicles equipped with enabled Bluetooth™ networking devices, including cellular phones, mobile GPS systems, telephone headsets, and in-vehicle navigation and hands-free systems.
Every Bluetooth™ device has an electronic address, known as a MAC address, used to identify it to other network devices. Each roadside AWAM reader senses these addresses emitted by enabled devices as they pass the reader station.
For real-time applications, the AWAM reader then transmits the time and location of the device to the AWAM host processing system at Houston TranStar. As probes are detected at successive AWAM readers, the host system merges travel time readings to calculate average travel times and speeds for a roadway segment.
The MAC addresses read by AWAM are not directly associated with a specific user and do not contain any personal data or information that could be used to identify or "track" an individual's whereabouts. In addition, all addresses collected by AWAM are anonymized through encryption immediately upon receipt. Users who have privacy concerns are also able to turn off the Bluetooth discovery function of their device which prevents it from being read by AWAM at all.
Unlike the applications on a smart phone that use the GPS functionality, AWAM does not have the ability to "track" vehicles or devices everywhere they go. Also, unlike these applications, AWAM cannot correlate a device address with an individual or vehicle so determining who the device belongs to is virtually impossible. Alternative methods for gathering traffic data, such as those used by GPS (which is utilized by virtually every smart phone) or license plate recognition are more likely to warrant privacy concerns.
RFID AVI Toll Tags
The system uses Automatic Vehicle Identification (AVI) technology to collect the real-time traffic information. Houston was the first city to apply AVI technology for monitoring traffic conditions.
The AVI system operates through the use of AVI antennas and readers which are installed on structures along Houston area freeways. The AVI antennas and readers monitor the passage of vehicles equipped with transponder tags. The transponder tags are powered by a small battery which enables them to reflect signals transmitted from the antennas/readers.
The toll tag IDs read by the system are strictly used for estimating average travel times and are not used to "track" individual tags. Each tag ID is anonymized upon receipt and no personal information is stored by the system.
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.