Road departure protection systems can help reduce off-road accidents

Road departures can be fatal, especially since the majority of them happen on highways and rural roads. According to the US Department of Transportation Federal Highway Administration, approximately 55 percent of traffic fatalities in the U.S. involve a vehicle crossing the roadway or centre line. In Germany, 60 percent of fatal road accidents and 25 percent of non-fatal road accidents occur on rural roads, according to the German Federal Statistical Office DESTATIS.

Automotive supplier Continental says it is working on new Road Departure Protection systems – a base and an enhanced system – that aim to eliminate unintended road departures, preventing fatal accidents from occurring on highways and rural roads.

Avoiding roadway departure crashes, which currently are not completely covered by today’s lateral guidance Advanced Driver Assistance Systems (ADAS), is the motivation behind developing a system for road departure protection. Road Departure Protection systems expand today’s lateral ADAS by active road keeping in emergency situations, before reaching the physical limits of vehicle dynamics. Based on environment perception means like road edge detection or road course preview, the systems should actively intervene when unintentionally leaving the roadway. By utilising automated vehicle control, the systems keep the vehicle on the intended roadway and as a result better protect against rollover accidents or collisions with roadside obstacles or oncoming traffic.

The Road Departure Protection systems will automatically steer a vehicle back into its lane when it begins to inadvertently leave the road or cross the center line into dangerous oncoming traffic. The systems differ from Lane Keeping and Lane Departure Warning systems in that they specifically monitor the outside boundaries of the roadway and act with more authority to keep the vehicle within its intended space.

“The system serves as a virtual guard rail, protecting the vehicle and its occupants from accidentally leaving the road, ultimately minimizing the risk of a potentially fatal accident due to driver error, distractions or drowsiness,” said Steffen Linkenbach, Head of Systems and Technology for the Chassis & Safety Division, Continental North America. “The Road Departure Protection system enhances our driver assistance portfolio of products by adding an intuitive solution that goes beyond the warning phase by automatically steering the vehicle back into its lane while alerting the driver of the potentially dangerous situation.”

How the system works
The base system, which uses a forward-looking mono camera to detect roadway boundaries, monitors the driver’s steering angle and vehicle path through existing Electronic Stability Control (ESC) sensors and also uses chassis motion sensors to identify if the vehicle is crossing the road boundary. It then uses the existing ESC system to apply the individual wheel brakes to automatically steer the vehicle back on the road while simultaneously warning the driver and reducing the speed of the vehicle for safety reasons. This active intervention is signaled when the vehicle senses it is departing the road. The system’s performance is enhanced by road edge rumble strips, creating an opportunity for a combined vehicle plus infrastructure solution with high effectiveness. The system is designed with a driver intention recognition feature in the event that the driver does intend to leave the roadway for any reason.

Besides realising a Road Departure Protection system with a mono camera and ESC, Continental is working in parallel on an Enhanced System: A system that uses a stereo camera and a long-range radar for improved detection of roadway boundaries, particularly for country roads in Europe. The long-range radar and the stereo camera of the Enhanced System allow the generation of an occupancy map that contains information about the occupancy state of a tessellated area in the vehicle’s field of view. Based on this map, a further confirmation of road departure and potential collisions with solid borders like kerbstones, guard rails or construction site equipment is provided. The goal is to detect road boundaries, even when lane markings are missing. A coordinated brake and steering intervention will increase the efficiency of this system.

The further integration of road map data and on-board GPS can also support an advanced preview ESC feature that detects the course of the road before entering a curve. Based on the predicted upcoming road curvature, the driver is supported in situations where the driving dynamics are critical, for example with inappropriate speed during curve driving on a country road or tight curves, to keep the vehicle within the possible physical limits of the road. “With this cascaded approach, we are developing an advanced system function designed to address a significant proportion of traffic accidents and fatalities worldwide,” said Alfred Eckert, Head of Advanced Engineering within Continental’s Chassis & Safety Division. “Both systems have the potential to promote increased vehicle and driving safety and contribute to Continental’s Vision Zero, the goal of achieving zero traffic accidents.”