We previously showed that, in daytime, drivers responded to stopped and slow-moving lead vehicles gradually, rather than suddenly when optical expansion rate reached .006 rad/s. Here we examined whether this occurs in (simulated) nighttime driving. We recorded expansion rate and lead vehicle’s time on screen at six driver inputs (from early- release accelerator to late- slam on brakes) to stopped and slow-moving vehicles. Two groups of participants responded differently to slowmoving vehicles; one group released the accelerator, and one group applied unanticipated-level braking. Responses to stopped vehicles occurred when expansion rate reached .005 rad/s, close to the .006 rad/s reported for immediate hazard perception. Time on screen was longer in daytime than nighttime for slow-moving vehicles for later inputs, suggesting that daytime drivers see the vehicle sooner and better estimate how much time they have to respond. Effects of cell phone conversation and expectancy were not significant.