Backing out of a driveway or parking spot into cross-traffic is a maneuver with an increased accident risk. Because of high shoulder lines and limited view, it is easy to overlook children or small persons stepping behind the car or other vehicles that approach from the sides and cross the path of the backing-out car. Existing systems, based on a reverse camera, help to discover persons or cars; however, will the driver pay attention to the screen? Typically his or her view will be directed backward because that is where the car is going.
Current systems do not always actively warn the driver, and they cannot stop the car. “We are not happy with this level of support,” said Wolfgang Fey, Director, Development of advanced driver-assistance systems at Continental in Lindau, Germany, during an interview at the 2011 Frankfurt Motor Show.
“Just to show an approaching vehicle or a person stepping behind the car does not ensure that the driver pays attention. And even if a warning is given, there is no guarantee that the driver will correctly interpret it and act in time.”
To date there is a conflict between the technical limitations of existing solutions and the U.S. NHTSA law proposal (mandated by the Cameron Gulbransen Kids Transportation Safety Act of 2007), which seeks to effectively eliminate the blind spot of new cars.
To reduce the number of people injured or killed in this type of accident every year, Continental has developed a new back-out assistance system called Rear Cross Traffic Alert (RCTA). The system is able to go beyond current back-out assistance functions; the RCTA detects approaching vehicles within a 30 to 40 m (98 to 131 ft) reach to the left and right. A warning will be given and the system can be configured to autonomously stop the car if the calculated trajectory of the approaching vehicle or pedestrian could result in an impact.
The new driver assistance solution is based on radar technology that is also used in blind-spot detection (BSD) systems. Two short-range sensors with 120° detecting angle, located behind the rear bumper corners, cover the rear and the sides of the car. In contrast to BSD, however, the technical requirements to the radar sensors are much higher in the case of RCTA.
To achieve a sufficiently precise scan of the vehicle environment, the supplier had to improve sensor precision. “With RCTA, the challenge is to precisely calculate the trajectory of a crossing vehicle even if it follows a curved trajectory,” explained Wilfried Mehr, Head of Business Development for advanced driver-assistance systems. “The new generation of radar sensors provides the precise information on speed, direction, and distance of the crossing vehicle which we need.”
Cars and cyclists are detected from a minimum speed of around 5 km/h (3.1 mph) and up to around 30 km/h (18.6 mph). Pedestrians can also be detected if they approach the vehicle swiftly and without hesitating.
“We prefer two sensor system options for this type of driver assistance,” Fey said. “One is radar technology, which can be either 24 GHz or 77 GHz depending on the economic boundary conditions of the technology. The other suitable sensor type is a camera with object recognition, preferably a stereo camera to get fast and exact distance readings.”
To avoid regional limitations of 24-GHz radar, the new RCTA is based on pulse radar in the ISM (industrial, medical, scientific) band where the limitations to the ultra wide band (UWB) do not apply.
Depending on the individual vehicle application, the RCTA human-machine interface can be adapted. The warning, for instance, can be given audibly or by an LED placed in the line of sight of the backing-out driver.
However, Fey himself is convinced: “It is a situation where we need to brake. It is beeping everywhere in new cars, and there is a risk that the driver could simply ignore the warning. It could also take the driver too long to realize the reason for the beeping.” For Fey the best solution is to activate the brakes and stop the car if a collision is imminent. “Of course, the driver must be able to override the system, if he steps on the pedal after the car has come to a stop,” Fey added.
Probably one of the strengths of the new RCTA approach is the way it can be integrated: “If the improved 24-GHz radar sensor hardware is integrated in the vehicle, three driver assistance solutions can be made available; BSD, lane-change assist, and RCTA will use the same sensor signals."
This multiple use of hardware will help to make driver-assistance systems affordable. “The more vehicles are equipped with BSD, lane-change assist, and RCTA, the safer traffic will be,” Fey stated. The current planning is to start series production of radar-based Rear Cross Traffic Alert in 2013, with an initial focus on the U.S.