Depending on the actions of the drivers piloting the oncoming cars, turning left at a busy intersection with no left-turn traffic signal can be a dangerous exercise. Should the approaching traffic include a motorcycle, the potential hazards can easily rise as the small vehicle can be hidden by road features or remain “unseen” by the turning driver because of inherent weaknesses in human perception.
Although they vary according to country and region, traffic statistics indicate that from 30% to 60% of all injury-causing auto accidents and up to one-third of all vehicular fatalities occur at road junctions. Whatever the case, if such a collision does occur, the driver making the turn is almost always held at fault.
Engineers at BMW Group Research and Technology in Munich recently demonstrated a left-turn assistant autonomous driver’s safety aid to help overcome the difficulties motorists encounter when performing this common maneuver. The system, which the researchers are evaluating in a 5 Series sedan, is intended to remove much of the peril of making turns into complex intersections by addressing both the visibility issues with sensors and the sometimes-tricky decisions regarding whether to proceed with automated braking in the hope of improving safety.
“We’ve developed an assistance system that helps drivers when they turn to the left by warning them of unseen, oncoming traffic,” said Project Manager Arne Purschwitz. “If necessary, it can prevent collisions by automatically applying the brakes.”
The novel technology is being pursued as part of the European Union-funded Intersafe 2 initiative, which aims to develop and demonstrate a cooperative intersection safety system that uses sensor fusion data and vehicle-to-vehicle (V2V) wireless communications to reduce accidents at road junctions. Intersafe 2 is a €6.5-million, cost-shared R&D program that is being conducted by a consortium of 11 European car makers, suppliers, and research institutes including BMW, NEC Europe Network Laboratories, Swarco Traffic Systems, Volvo Technology, and Volkswagen.
The BMW system activates automatically as soon as the car’s sensors determine that the vehicle is entering a left-turn lane and it registers the driver’s intention to turn left. Recognition of the lane location is accomplished in two ways, according to company researchers. The GPS sensor in the car’s navigation system establishes the car’s position within a meter and then matches that point with known intersections on its digital map, while a camera-based image-recognition system reads the road markers that indicate the presence of a left-turn lane.
When the driver engages the car’s turn signal, the system triggers three front-mounted laser scanners that map the area forward out to a range up to 325 ft (100 m). The left-turn assistant uses that data to identify oncoming cars, trucks, and motorcycles. If the sensors detect vehicles approaching from the opposite direction but the car continues into the intersection, the system sounds a warning alarm and presents hazard symbols on the instrument panel and head-up displays, while immediately applying automated braking to prevent a collision.
This autonomous intervention deliberately occurs with no prior warning, the researchers said, because an instant response is vital to prevent an accident in these circumstances. Braking is instituted only up to speeds of 6 mph (10 km/h), which leaves drivers free to cross the traffic stream at high speed without electronic controls if they so choose.
As soon as the driver touches the brakes, however, the system halts any automatic braking input, releasing the car so normal driving can continue. To maximize safety the driver can always override the left-turn assistant. If the driver needs, for example, to guide the car to the roadside to clear the way for an emergency vehicle, he or she can do so at any time merely by hitting the gas pedal.
V2V enhances benefit
If the left-turn assistant is augmented with V2V communications, which enables cars to “know” where other vehicles around them are located, greater safety will result, according to company spokespersons. The BMW 5 Series test sedan is fitted with a V2V unit, which boosts the range of its vehicle-recognition function to 820 ft (250 m). It also allows the safety system to detect the presence of unseen vehicles that are equipped with V2V. This capability can be helpful, for instance, when a vehicle follows a line of cars through a left turn, in which case its sensors would probably be screened by the preceding cars.
BMW engineers also recently conducted another test scenario that highlighted the benefits of this combined function. In this case, the research car approached a BMW R 1200 GS motorcycle fitted with a V2V unit. As before, the data provided by the camera-based image-recognition system and laser scanners enabled the left-turn assistant to register the lane markings, the left-turn arrow, and the distance to the center line and stop lines. When the turning driver engaged the car's turn-signal indicator, the system activated.
“The car and the motorcycle communicated with one another via the car-to-x [V2V] interfaces as the motorcycle approached,” explained Udo Rietschel, a development engineer on the project. “The car and motorcycle exchanged information on the type of vehicle, its position and speed, as well as dynamic data such as its steering angle and whether the indicators were activated.” The motorcycle’s safety system then employed this information to determine that the car driver planned to turn left and move in front of it. An algorithm then calculated the vehicles’ trajectories and decided if a collision was likely.
In critical situations, the motorcycle would take measures to warn the car driver by taking steps to raise its visibility—by intensifying the brightness of the cycle’s headlights as well as other lights on its sides and mirrors. If its safety system calculates an acute risk of collision, the motorcycle’s horn would also sound. Should the car continue entering the intersection, the left-turn assistant would brake the car automatically while activating the appropriate driver alerts and warnings.
BMW's left-turn assistant system, which is still at the developmental stage, was recently demonstrated publicly at a closed-off road junction in Wolfsburg, Germany. If the engineers can prove the viability of the technology, the company could potentially introduce it into production vehicles by 2016.