TIRTL

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TIRTL receiver on a portable stand

The TIRTL (The Infra-Red Traffic Logger) is a type of traffic counter. It has the ability to record volume, speed, and classification on a bi-directional, multi-lane roadway. This product is produced by CEOS Pty Ltd and marketed by CEOS Industrial Pty Ltd. It does this by placing a receiver unit and transmitter unit on either side of the road. The transmitter sends two cones of infrared light across the roadway and the receiver records the cones being made and broken; this creates two parallel beams and two crossed beams.

The unit has a single board computer (x486) running Debian Linux. The computer interpets the supplied traffic classification table (FHWA Scheme F or user supplied) and composes the axle events caused by the parallel beam breaks into a classified vehicle. The devices has two RS232 ports for data transfer and optional GSM & PSTN modems. The unit was originally developed to provide a verification for intersection safety cameras deployed in Victoria.^[1] It was first deployed in Australia in July 1998.^[2] The unit was introduced to the North American market during the 2004 NATMEC (North American Travel Monitoring Exhibition & Conference) and first deployed in May 2006.

1 Details of operation
2 Performance review
3 References
4 External links

[edit] Details of operation

TIRTL beam diagram

The TIRTL transmitter's infrared cones cross each other and form two straight and two diagonal beam pathways. When a vehicle crosses the beam pathways, the TIRTL records two beam events; it records one from the vehicle breaking and one leaving the beam pathway. These two beams events are recorded for all four beam pathways. Thus, eight time-stamped events are generated per axle. The velocity is derived from the timestamps of these beam events.

Since the velocity of each vehicle wheel is known and a timestamp is recorded for each axle crossing each beam, the interwheel (or interaxle) spacings can be determined. Once the interaxle spacings are known, it is compared to a table of interaxle spacing ranges stored in the unit to determine the correct classification of the vehicle. The results are stored on a per vehicle basis.^[3]

[edit] Performance review

The Minnesota Department of Transportation, in conjunction with 16 participating state DOTs, conducted a pooled fund study called PNITDS (Portable Non-Intrusive Traffic Detection System). The study's goal was to fabricate a portable non-intrusive detection system and then compare it with similar non-intrusive devices already available. This study also provided an opportunity to compare the already available devices to each other.

The final report stated that the TIRTL had an accuracy rate ranging between 94% and 97% correctly classified.^[4]

[edit] References

^ MORE SAFETY CAMERAS GET GREEN LIGHT. Department of Premier & Cabinet, Victoria, Australia. Retrieved on 2006-02-08.
^ Overview of TIRTL. Retrieved on 2006-07-13.
^ “Section 3.1: Vehicle Detection using 'Beam Events'”, TIRTLsoft V1.6 for Windows User Manual (PDF), v1.0.1 Imperial, CEOS Industrial, 13.
^ Kotzenmacher, Minge, et. al.. "Evaluation of Portable Non-Intrusive Traffic Detection System" (PDF). Minnesota Department of Transportation, Research Services Section. Retrieved on 2006-06-20.