Intersection and Turn Assist
Intersection and turn assistance can warn, brake or support steering for crossing, oncoming and vulnerable-road-user conflicts, but it does not determine that a junction is safe to enter.
Why intersections are demanding
Straight-ahead AEB can estimate closing speed along a relatively simple path. At a junction, several paths cross at different angles. The vehicle must consider:
- oncoming traffic while turning across a lane;
- vehicles crossing from either side;
- pedestrians and cyclists entering the intended path;
- occlusion by buildings, parked vehicles or other traffic;
- signals, signs and right-of-way rules;
- the driver's steering and acceleration.
Wide-angle cameras and corner radar can expand the field of view. Software predicts the future paths of the vehicle and detected road users, then estimates whether those paths conflict.
Typical functions
The terminology varies, but common behaviors include:
- junction AEB: brakes for crossing or oncoming traffic;
- turn-across-path braking: reacts when the driver turns across an oncoming vehicle;
- vulnerable-road-user turning support: reacts to a pedestrian or cyclist crossing the turn;
- front cross-traffic warning: warns before the vehicle enters a partially obscured junction.
One label may include only one of these cases. Performance also varies by turn direction, target type and speed.
Traffic lights and stop signs
Some supervised Level 2 systems can identify signals or stop signs and slow or stop. That is a different function from collision-triggered junction AEB. A red-light response follows a traffic-control rule; AEB reacts to an imminent collision.
Neither capability transfers responsibility when the system is Level 2. The driver must verify the signal state, stopping position, right of way and behavior of other road users. Route-guided Level 2 operation is covered in Point-to-Point Navigation at Level 2.
Testing the real capability
A meaningful result identifies the scenario rather than saying only that the vehicle has "intersection assist." Important variables include:
- target vehicle speed and approach angle;
- whether either vehicle is accelerating or braking;
- daylight, darkness and adverse weather;
- adult, child, cyclist or motorcycle targets;
- partial obstruction and late target appearance;
- warning timing, impact-speed reduction and full avoidance.
Automatic braking can reduce severity without preventing a crash. A pass in one standardized test does not demonstrate coverage of every intersection.