Driving Simulator Study Finds Lane Departure Warning Systems Can Reduce the Percent of Drive Spent Outside of Travel Lane by 50 Percent Compared to Manual Driving.

Assessment of two lateral support systems measures impact on the percent of drive outside travel lane, lane position variability, lane departure duration, mean speed and user satisfaction.

Date Posted

To Alert or Assist: Comparing Effects of Different Lateral Support Systems on Lane-Keeping

Summary Information

Lateral support systems have the potential to reduce road-departure crashes by decreasing the probability that a vehicle will leave its intended travel lane. Two lateral support systems on the market are Lane Departure Warning (LDW) and Lane-Keeping Assist (LKA). LDW systems issue a visual, audible, or haptic warning to alert the driver that the vehicle has crossed a lane boundary. LKA systems actively move the vehicle back into its lane by either applying steering torque or light differential braking.

This FHWA study compared lane-keeping behavior when drivers drove without lateral assistance, with LDW, or with LKA. The goals of this study were to:

  • assess the effect of each type of lateral support system on lane-keeping ability during conditions in which a driver unintentionally leaves their travel lane
  • assess how drivers respond to lateral support systems triggered in response to an intended lane departure, and
  • determine whether drivers respond appropriately to lane departures following an unexpected lateral support system failure.

User acceptance of each system was also examined.


A fixed-base driving simulator was used to compare lane-keeping behavior when drivers were controlling the vehicle without lateral assistance (i.e., manual control) or were assisted by LDW or LKA systems. Seventy-two licensed drivers from the Washington, DC, metropolitan area participated in the study. All participants drove on a 22-mile-long undivided two-lane road in a semirural setting using the simulator. One-third of participants drove with LDW, one-third drove with LKA, and one-third drove without either lateral support system. Simulated wind gusts were used to induce lane departures throughout the drive. Following the drive, all participants completed a nine-item questionnaire that provides separate measures of the usefulness and user satisfaction with new in-vehicle technologies.



  • Drivers with LDW systems had better lane-keeping than those in the LKA or manual conditions. Compared to manual driving, Drivers with LDW spent less of the drive outside of their lane (1.51 percent less), returned to their lane more quickly when a lane departure occurred (58 percent faster), and held a more constant position while in their lane (15 percent less in mean lane position variability).
  • Slower travel speeds were found for manual driving conditions than those with lateral support systems, suggesting that the difference in lane-keeping ability was not due to the tradeoff between lane-keeping and speed.
  • Drivers’ lane-keeping in the LKA condition did not match those in the LDW condition, but the group maintained similar levels of lane-keeping to participants in the manual condition while driving faster (5 percent faster) and showed reduced lane-departure durations (38 percent reduction), suggesting that LKA improved drivers’ lane-keeping.
  • Participants gave the LDW and LKA systems positive ratings for both user satisfaction (average rating of 78 out of 100) and usefulness (average rating of 83 out of 100).


Condition Mean of Drive Spent Outside Lane (%) Mean Lane Departure Duration(s) Mean Lane Position Variability (ft) Mean Speed (mi/h)
LDW 1.51 1.21 0.99 44.9
LKA 3.27 1.78 1.12 45.19
Manual Driving 3.02 2.86 1.17 43.14


Results Type