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Traffic Data Recorder


A metal protective case with a single handle, two lockable latches, and a hinged lid, contains an built-in instrument whose console is revealed when the lid is opened.

A conventional tape recorder (a Realistic CTR-41) is integrated into the console. Below the tape recorder is a row of rocker switches and a green charge indicator. To the right of the tape recorder is a six-digit LED display. Below the display is a keyboard consisting of a white twelve-key hexadecimal keyboard and eight blue function keys (seven + “clear entry”).

The left side of the case exterior contains several ports for connecting sensors and cameras, charging batteries, and displaying data on an external computer terminal.

The a hollow in the case beside the console contains the following items:
– One Cerlox-bound operation manual.
– One traffic data recorder summary card in a plastic liner
– Two audio tapes, one of which is in its plastic case.
– One plastic shoulder strap corresponding to attachment points on either side of the case.
– One charging cable for attaching to a 12v DC lighter port.
– One 25-pin data cable with two one plug end and two socket ends.
– One coaxial cable with a single socket end.
– Two case keys attached to a piece of red plastic.
– One Toronto Transit Commission business cards for Frank J. Ahlin.

Accession Number:

Alternative Name:

Primary Materials: Iron Alloy, Aluminum Alloy, Plastic


The front of the console includes the following identifying information: “TDR NO. 703”
“703” is also embossed on a grey adhesive label on the left side of the case.

A stylized “LA” logo, representing Leo Ahlin, Computer System Consultant, is printed on the instrument console above the audio recorder.

The brand of the case, “HAKUBA”, is stamped on part of the carrying handle.

Dimensions (cm): Height = 17, Width = 34.5, Length = 46/


This instrument was developed to study traffic patterns. It measures and records vehicle speed using sensors attached to its sensor ports. Data is read to magnetic audio tape and can be transferred to a computer using the data port. The instrument can also control a 16mm film camera in order to record vehicle license plates.


This instrument is in very good cosmetic condition with only light signs of dirt and wear. Unusually, the foam lining of the interior of the case does not appear to be degrading. There are light dents and abrasions on the outside surface of the case.

Associated Instruments:


Leo Ahlin, Computer System Consultant. Rexdale, Ontario, Canada.

Date of Manufacture: c. 1979.


Note that this instrument was developed and used at the University of Toronto Department of Civil Engineering (currently the Department of Civil & Mineral Engineering of the University of Toronto Faculty of Engineering). Because there is no corresponding collection, and the instrument was obtained from the Department of Chemistry, it is catalogued with other material from the Department of Chemistry.

This item was acquired from the IT Services of the University of Toronto Department of Chemistry on March 29, 2023.

Additional Information and References:

Ezra Hauer, Frank J. Ahlin, and J.S. Bowser. “Speed Enforcement and Speed Choice.” Accident Analysis and Prevention 14, no. 4 (1982): 267–78.

Ezra Hauer and Frank J. Ahlin. The Effect of Speed Enforcement on Driver Speed Choice. Department of Civil Engineering, University of Toronto, Transport Canada Contract DTS 483-103, 1979

Frank J. Ahlin. An Investigation into the Consistency of Driver’s Speed Choice. MA. Thesis. Department of Civil Engineering, University of Toronto, 1979.

Historical Notes:

The Traffic Data Recorder (TDR) was developed and built by Frank Ahlin, then a graduate student at the University of Toronto Department of Civil Engineering. It was built for (and presumably funded by) a research study conducted for Transport Canada that studied the problem of driver speed choice. This refers to the effect of traffic enforcement on the behaviour of drivers. These studies, conducted in the fall and winter of 1979, were led by Dr. Ezra Hauer, a Professor of Civil Engineering at the University of Toronto.

In an email communication received on 1 April, 2023, Hauer noted that “There were no similar instruments available at that time.”

This instrument was developed to investigate the extent to which the enforcement of speeding laws by police actually affected driver behaviour. This was a controversial and poorly understood problem in public safety and law enforcement. Speed enforcement was unpopular both with drivers and the police.

A series of four experiments was conducted on semi-rural roads in the counties of Halton and Peel west of Metropolitan Toronto. This involved the cooperation of Halton and Peel police. They gathered data at three general locations: an “upstream” site located at a point before the driver arrived at the enforcement site, the enforcement site itself , and a site between 1 and 2.5km “downstream” from the enforcement site. Police did not issue tickets during the experiments so as to present a consistent “enforcement symbol”. Data was also gathered when the enforcement site was no longer present in order to determine the extent and duration of the enforcement on driver behaviour.

The experiments were described as follows:
“In the first experiment, passing vehicles were exposed to a clearly visible police cruiser for 1 day. The second experiment was similar except that the cruiser came into the driver’s view suddenly. In the third experiment, five consecutive days of enforcement were used. In the fourth experiment, enforcement took place on two days with a pause of 3 days in between.” [Hauer, Ahlin, and Bowser 1982, 269]

The instrument was used to record vehicle speed using pressure sensors, and to trigger a 16mm movie camera in order to photograph the corresponding vehicle license plates at each measurement location. License plate data was used to measure the effect of enforcement on identifiable vehicles. Data was recorded to magnetic storage on a standard audio cassette tape and subsequently analyzed on a computer. The experiments produced a database of 116,000 valid speed records. This figure excludes records lost through equipment errors, observer efforts, and other difficulties. Data loss was much more of a factor in the earlier two of the four experiments. The experimental data was described in detail in a 1979 report to Transport Canada, and summarized in a 1982 article published in the journal Accident Analysis and Prevention.

The experiments produced a number of findings. It notably confirmed earlier findings of a “downstream distance halo”, a measurable reduction in speed, that “follows the general form of exponential decay” whereby “…the effect of enforcement is reduced by half for approximately every 900 m downstream from enforcement.” It also found a correlation between the “dose” of enforcement (the number of consecutive days in which the enforcement appeared) and the duration of the “time halo” (the period in which driver behaviour was affected by enforcement). [Hauer, Ahlin, and Bowser 1982, 277]

  • Donated to UTSIC