## Safe-D: Safe Following Distance Indicator to Prevent Rear-end Accidents

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Rear-end collisions account for 33% of accidents on U.S. roads. This class of accident accounts for 44% of fatalities (50,000 deaths per year).

Detailed analysis of rear-end collision accident reports showed that the majority of rear-end collisions occur on straight highways, in good weather conditions, good road conditions, and during daylight hours. Further, new old, and experienced drivers were equally likely to be involved in rear-end accidents.

A detailed analysis of a physics-based model of rear-end collisions identified the velocity of the lead/follow cars, the braking efficiency of the lead/follow cars, and the reaction time of the follow car as the main factors in bringing the following car to a stop before colliding with the lead car.

This model-based analysis showed that although the reaction time of the follow car is important, what is more important is the following distance between the cars. If the follow car is too close, no amount of braking can prevent a collision.

The interesting fact is that there is NO VISUAL INDICATION provided to the driver of the following car to know if they have a safe following distance or not. Furthermore, the safe following distance is a non-linear function of the difference in initial velocities and the difference in braking efficiencies between the lead and follow car.

The U.S. drivers exam study guide recommends "maintaining a 2-3 second" gap between cars. First, how does a driver measure this time? Second, this guideline does not take into account the velocities and braking efficiencies of the cars.

Analysis of data from a video recording cars on a highway, showed that 63% of the cars did not maintain a safe following distance given the velocities of the cars.

Based on the analysis described above, it is clear that REAR-END COLLISIONS COULD BE REDUCED by providing the following car with a SAFE FOLLOWING DISTANCE INDICATOR.

This team has proposed a product concept, called SAFE-D, that mounts on the rear of a lead car. One example could be a license plate frame.

The device has a micro-processor/accelerometer/GPS to calculate safe following distance and turn the device on/off. The microprocessor also controls the directed-light mechanism (see below).

The device uses a novel directed-light mechanism such that the following car can only see the "too close" warning when the following car is within the unsafe following distance. This directed light mechanism uses coupled lenses to direct the light. (This is the same mechanism used at airports to guide aircraft to a safe landing angle as the aircraft approaches the runway).

The device can be retrofit on cars. It is powered by its own battery, and is rugged for all weather conditions.

Although the device cannot eliminate rear-end collisions, it can significantly reduce the likelihood of a collision for the car with the SAFE-D device installed.

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