Effect of ESC (electronic stability control) on tree and pole impacts with focus on rear impacts.

OBJECTIVE

The effect of ESC (Electronic Stability Control) was investigated for the rate of crash exposure, serious injury and fatality in pole and tree impacts. Field data was analyzed by crash type (front, side, rear and rollover) and model year (MY) before, during and after the implementation of ESC.

METHODS

The number of pole and tree impacts was determined for four groups of vehicle model years (MY): 1981-1989 MY and 1990-2002 MY before the introduction of ESC, 2003-2009 during the phase-in of ESC and 2010-2020 MY after essentially all vehicles were equipped with ESC. Collisions were grouped by front, side, rear and rollover. Three databases were analyzed: 1990-2020 FARS, 1990-2015 NASS-CDS and 2017-2020 CISS. Vehicle registration was obtained from IHS Markit to determine the rate of pole and tree impacts per 100,000 registered vehicles. The same vehicle selection criteria was used for vehicle registration and crash data.

RESULTS

Fatalities dropped 65.2 % (95 % CI, 63.0-67.4 %), z = 43.7, p < 0.001 into poles and 60.3 % (95 % CI, 59.0-61.5 %), z = 72.4, p < 0.001 into trees in vehicles equipped with ESC comparing 1990-2002 MY to 2010-2020 MY vehicles. Seriously injured occupants in crashes with poles dropped 75.9 % (95 % CI, 75.0-76.9 %), z = 116, p < 0.001 between 1990 and 2002 MY and 2010-2020 MY vehicles. There was a 65.2 % (95 % CI, 64.4-65.9 %), z = 141, p < 0.001 reduction in tree impacts. The crash exposure to pole impacts dropped 36.0 % (95 % CI, 35.8-36.3 %), z = 252, p < 0.001 from 80.77/100,000 registered vehicles in 1990-2002 MY vehicles to 51.69/100,000 in 2010-2020 MY vehicles. There was a 61.0 % (95 % CI, 60.8-61.2 %), z = 434, p < 0.001 reduction in tree impacts. For rear impacts, fatalities dropped 82.9 % (95 % CI, 71.3-94.4 %), z = 9.37, p < 0.001 into poles and 74.8 % (95 % CI, 67.8-81.9 %), z = 14.8, p < 0.001 into trees. Serious-injury in rear impacts with poles and trees were essentially eliminated in 2010-2020 MY vehicle crashes. There were significant drops in fatalities in side and frontals impacts and rollovers in vehicles equipped with ESC.

CONCLUSION

ESC helps the driver maintain vehicle heading and significantly reduced the rate of serious injury and fatality in off-road impacts with poles and trees. The benefits of ESC may not be realized with impairments when the driver does not appropriately steer the vehicle.