TIRTL

[1] It uses infrared light cones sent from a transmitter to a receiver situated on opposite sides of the road perpendicular to the flow of traffic.

[2] These options allow for real time applications, such as variable message sign triggering and traffic enforcement, as well as data logging for statistical purposes.

It is currently in use in Australia, New Zealand, the Netherlands, Belgium, Luxembourg, Norway, Germany, Denmark, Sweden, South Africa, Turkey, India, Singapore, the United States, Canada, and Mexico.

[3] Primary applications for this device include speed verification for enforcement purposes, traffic volume and density data collection for both statistical and real time usage, and vehicle classification by axle spacing.

[3] The unit was originally developed to provide secondary verification for intersection safety cameras deployed in the state of Victoria, Australia.

TIRTL transmitter's infrared cones cross each other and form two straight and two diagonal beam pathways.

[2] 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.