TecDay Real Life Safety
Nov 12, 2008
Speed Limit Assist: Electronic image processing system detects speed-limit signs as the car drives past them
A newly developed Speed Limit Assist system detects speed-limit signs in milliseconds, in real time, and reminds the driver of the current speed limit. The system, which will be available for the new E-Class and the model year 2009 S-Class, is based on intelligent, electronic image processing.
Throughout the world, failure to adjust speed is the root cause of the most
road accidents and the road accidents with the gravest consequences. The new Mercedes assistance system can remind drivers of the speed limit currently in force and, in doing so, help them to be safer on the road. The speed limit appears on a display in the instrument cluster and remains visible until the speed restriction is lifted or changed. 
A windscreen-mounted camera monitors the area in front of the car on a permanent basis and has a trained eye for road signs. That's because a computer scans the camera image for round surfaces only and then highlights these. In the next step, a system of algorithms filters out all objects that are round but do not resemble traffic signs. Finally, a comparison with stored patterns eliminates all but those objects which the system is programmed to detect: round traffic signs
indicating the speed limit. The symbols are sent to the cockpit display, meaning that the driver is always aware of the current speed limit and can adjust the car's speed accordingly.
Some of the speed-limit signs in Europe – for example those seen when entering or leaving towns – are rectangular, however. In such cases, the assistance system also scans the data stored on the navigation system's digital map to check the plausibility of the camera image. The last speed limit detected disappears from the display in the instrument cluster as soon as the car enters a built-up area,
for example.
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