• Speed monitoring systems use a range of different technologies
• The first ideas are almost as old as the car itself
• The widespread design of stationary measuring systems in Germany led to them being called “nesting boxes”
• “33 Extras”: exhibits of motoring culture at the Mercedes-Benz Museum

Stuttgart. 160 vehicles and a total of 1,500 exhibits are presented in the varied permanent exhibition of the Mercedes-Benz Museum. The “33 Extras” are a particular highlight: they can bring the history of personal mobility and motoring culture to life using details that are often surprising. The Mercedes-Benz Museum Inside newsletter series draws attention to the “33 Extras” and focuses on their background stories. Today’s edition is all about radar speed traps.

28/33: Radar speed traps

The unexpected red flash: For more than 60 years, motorists in the Federal Republic of Germany have been “flashed” when they pass a speed camera set up by the police or public order authority at too high a speed. The flash – usually red – set off by the unit is part of the process of photographing the licence plate number and driver. The car’s speed is measured beforehand using various techniques – including radar. This has also resulted in the systems being called “radar speed traps”.

Stationary: Speed cameras mounted in a stationary location often use contact strips embedded in the road surface. They register when a car passes over them and calculate the speed from this. If the speed limit applicable at that point is exceeded, the flash and camera are triggered. They are often mounted in a housing with round openings (the flash at the bottom, the camera above), which is mounted on a pole. This shape, reminiscent of a nesting box for birds, has led to the cameras being called “nesting boxes”. The exhibit on show as one of the “33 Extras” in the Mercedes-Benz Museum is a “nesting box” made by Traffipax.

Science fiction: Ideas for monitoring the speed of road traffic with technical equipment are almost as old as the car itself. In his science fiction novel “A Journey in Other Worlds”, US writer John Jacob Astor, who died in the sinking of the Titanic, described back in 1894 how the traffic police might in future use serial photographic images to determine the speed of vehicles in urban traffic: “The policemen on duty also have instantaneous kodaks mounted on tripods, which show the position of any carriage at half- and quarter-second intervals, by which it is easy to ascertain the exact speed...” Today’s solutions for speed monitoring are based on a principle that is, at least, similar. They register when vehicles enter and leave a monitored zone and calculate the average speed.

Send and receive: The first technical systems for speed measurement used in practice in the Federal Republic of Germany were, however, mobile. The measuring device emitted radar waves which were reflected by vehicles and the changed frequency was registered. From the change in frequency during this send and receive action, the speed of the respective vehicle could be calculated. In February 1959, the traffic police near Düsseldorf used the “VRG 2 traffic radar unit”, supplied by the manufacturer Telefunken, for the first time. Until that time, it had not been possible to measure vehicle speed accurately in road traffic.

Road safety and local government finance: The main purpose of speed measurement is to improve road safety by monitoring compliance with speed limits. This applies in particular to the maximum speed limit of 50 km/h in built-up areas, which has been in force in the Federal Republic of Germany since 1 September 1957. Soon, however, municipalities realised that the fines imposed for speeding violations could also boost local or city finances. Since then, there have been repeated disputes about the positioning of these cameras: are they really particularly critical points in road traffic? Or are they chosen more specifically because they promise high levels of income?

Technical developments: Since the first radar measurements in road traffic more than 60 years ago, the corresponding techniques have been further developed. There are many different kinds of fixed installations and mobile measuring devices. Speeds are measured by contact loops, radar, lidar and light barriers, among others. At the same time, it has become much easier for drivers to control their speed inside the car. This is achieved, for example, using the cruise control system, which Mercedes-Benz first presented in its S-Class of the 116 model series and the SLC sports cars of the C 107 model series in 1975. Later, this was supplemented by the “limiter” function, which allowed the driver to set a maximum speed.

Motorsport: Motor racing is all about achieving maximum speeds on the track. In the pit lane, however, a maximum speed limit has been in force since the mid-1990s in the Formula One premier class and this is currently 80 km/h. Even minor infractions result in time and money penalties for the drivers. The remedy is that modern racing cars usually have a pit lane speed limiter built in, which is operated by the driver.

Driver assistance: Over time, cars have been equipped with an increasing number of aids to assist the driver in adhering to prescribed maximum speeds. Today, for example, the Active Speed Limit Assist function in Mercedes-Benz cars can recognise traffic signs using a camera and detect the applicable speed limits even in unclear situations. If activated by the driver, Active Distance Assist DISTRONIC automatically processes this information and adjusts the vehicle’s speed accordingly.

As a precautionary measure against the spread of coronavirus SARS-CoV-2, the Mercedes-Benz Museum is temporarily closed.