Visual in-car warnings: how fast do drivers respond?

In-car technology allows for personal feedback on driver behavior. One development is to place beacons that can trigger an in-car warning 500 meters before an upcoming lane closure and 350 meters before road objects (rumble strips) appear. What is not known is whether this is enough to allow an effective and timely lane change. Moreover, it is not known how quickly people respond to in-car signals in general. We investigated this using a desktop based driving simulator task. In a within-subjects study participants drove at both 130 km/h and 80 km/h on a three lane highway. A simulated in-car warning system showed in the bottom of the screen when a lane change was needed. We measured reaction time and lane change distance. The driving task was either combined with an audio task at different levels of conversation complexity or performed without it. The initial reaction time was significantly different between audio conditions, but not between driving speeds. Changing distance was on average larger for higher speeds (M = 140 m at 130 km/h) than lower speeds (M = 100 m at 80 km/h). There was no significant effect of audio conditions. Although this average complies with the intended design of 350 meters, within the testing group (N=24) there were 11 subjects who occasionally failed to change lanes in time (20 trials total) - even in trials without audio tasks. This suggests that providing in-car warnings 350 meters before an obstacle is not always enough to allow a timely lane change.