How to calibrate a speed and red light camera

A few years ago I spotted something of note while out driving – a forest of traffic cones set up around the combined speed and red light camera system at the intersection of Mount Alexander Road and Maribyrnong Road in the Melbourne suburb of Ascot Vale.

Calibrating a combined speed / red light camera

I pulled over to take a closer look, and found a car belong to SGS S.A. – a Swiss multinational company which provides inspection, verification, testing and certification services.

Contractor at work calibrating a combined speed and red light camera

There was a piece of tripod mounted equipment labelled TIRTL on one side of the intersection.

Infrared sensors at one side of the intersection

And a second unit on the other side.

TIRTL ('The Infra-Red Traffic Logger') device being used to calibrate a speed camera

Also connected to an equipment box.

Second set of infrared sensors on the other side of the road

So what was it all for? The green thing labelled ‘TIRTL’ is actually a ‘The Infra-Red Traffic Logger‘ unit:

The transmitter sends two cones of infrared light across the roadway, and the receiver records vehicles as they break and remake these cones. TIRTL transmitter’s infrared cones cross each other and form two straight and two diagonal beam pathways.

When a vehicle crosses the beam pathways, 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 timestamped events are generated per axle. The velocity is derived from the timestamps of these beam events.

This velocity data is then compared with the velocity data calculated by the speed camera system itself, as part of the testing and maintenance procedures required under the Road Safety (General) Regulations 2019.


– Speed accuracy and speed reliability testing
– Camera system asset inventory
– Camera system sensor evaluation

Which leads to the issuing of an annual test certificate for each camera.

Footnote: and another one

I’ve also found the speed and red light camera at the corner of Flinders Street and William Street undergoing testing.

Contractors checking up on a combined speed and red light camera

Back in 20114 it was the speed camera which issued the most fines in Victoria, with 20,774 in one quarter. While in 2017 it claimed the dubious honour of Victoria worse location for motorists running red lights, with almost 2000 fines issued in one quarter.

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9 Responses to “How to calibrate a speed and red light camera”

  1. Philip says:

    Those Tirtl counters are very clever. They can give you all the axles of all the vehicles passing because they only see what’s just above the ground. Then they instantly turn that into vehicle lengths and speeds. Of course they have to be supervised or arseholes will destroy them. They can also be mounted permantently in modified kerb sections, which you’ll see in some places with little black windows to allow the beams to shoot across the road.

  2. Jesse says:

    The intersection of Canterbury Rd and Elgar Rd in box hill is where new speed camera technologies are tested and verified. At any given time they have several experimental speed cameras installed, plus at least two conventional approved speed cameras to verify results and actually issue fines. Short version of the story: DO NOT ATTEMPT TO SPEED through that intersection!

  3. Andrew Cee says:

    It is good to know cameras are carefully calibrated. I will guess the speed detection indicator cameras on the Princes Highway near Geelong will never work again.

    I think after the William Street camera, the one at Fitzroy Street and Lakeside Drive was very successful at revenue raising. I saw so many cars flashed there. So many 40 km/h signs but apparently no one could see them.

    • Marcus Wong says:

      The speed check units on freeways have all died over the years – there also used to be one on the Hume Freeway northbound at Beveridge, and westbound on the Western Freeway at Ballan.

      Defective speed check units on the Western Freeway westbound at Ballan

      • Aiden Webber says:

        There also used to be another one on the Hume just west of Wodonga (Melbourne Bound only), and when I travelled past it back in October it didn’t seem to be working at all.

        They were also on the Calder Freeway (Melbourne Bound) at the Bulla-Diggers Rest Rd Overpass in Diggers Rest, An Eastbound speed Checker on the Western Fwy at the same Ballan location, and another Westbound speed checker on the Western Fwy at the Gillies Street Nth overpass in Ballarat.

        TBF, they had become increasingly redundant over the years with quite a lot of cars these days having built in (and thus probably more accurate) current speed displays alongside the existing speedometers, and the amount of standalone GPS systems that have a ‘your current speed’ in KM/H displayed as well.

  4. Paul Westcott says:

    The speed check system on the Melbourne-bound lanes of the Princes Freeway, mounted on the Beach Road (Avalon Airport) overpass, has been out of action for well over a year.

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