Crashes resulting from lane departures can be among the deadliest collisions. In 2015, nearly 13,000 people died in single-vehicle run-off-road, head-on, and sideswipe crashes where a passenger vehicle left the lane unintentionally. Technology designed to help drivers avoid unintentional lane departures can prevent these crashes. Other technologies aim to keep drivers from drifting out of lanes, either by providing warnings or steering corrections when they cross a lane line without signaling or by actively centering them within their lanes. Lane departure warning (LDW) first became available in the United States on the Infiniti FX35 in model year 2005 and is becoming increasingly available on new passenger vehicles. In model year 2017, lane departure warning was available on 63 percent of new U.S. passenger vehicle series as standard (6 percent) or optional (57 percent) equipment.
The purpose of this study was to evaluate the effects of lane departure warning (LDW) on single-vehicle, sideswipe, and head-on crashes.
Police-reported data for the relevant crash types were obtained from 25 U.S. states for the years 2009-15. Observed counts of crashes with fatalities, injuries, and of all severities for vehicles with lane departure warning (LDW) were compared with expected counts based on crash involvement rates for the same passenger vehicles without LDW, with exposure by vehicle series, model year, and lighting system standardized between groups. For relevant crashes of all severities and those with injuries, Poisson regression was used to estimate the benefits of LDW while also controlling for demographic variables; fatal crashes were too infrequent to be modeled in this way.
Crashes considered relevant to lane departure warning included single-vehicle, head-on, and sideswipe crashes where no crash-involved vehicle was changing lanes, merging, passing, turning, or backing prior to the crash, and which occurred on roads with speed limits of 40 mph or greater that were not covered with snow or ice.
Lane departure warning is preventing the crash types it is designed to address, even after controlling for driver demographics.
- Without accounting for driver demographics, vehicles with LDW had significantly lower involvement rates in crashes of all severities (18 percent), in those with injuries (24 percent), and in those with fatalities (86 percent).
- Adding controls for driver demographics in the Poisson regression model reduced the estimated benefit of LDW only modestly in crashes of all severities (11 percent, p<0.05) and in crashes with injuries (21 percent, p<0.06).
Since other studies have demonstrated that many drivers turn off their LDW system (because of an annoyance factor associated with the warnings, particularly audible warnings), the benefits would likely even be higher had they been keeping their systems on at all times. If half of these lane departure warning systems were turned off, then the reduction in crash involvements was only half of what it could have been.