Roadways are nearly ubiquitous parts of the modern landscape, but their impact on bats remain relatively unknown. We studied the influence of vehicular traffic on the behaviour of commuting bats near the Indianapolis International Airport. A previous study at this site documented that Indiana bats (Myotis sodalis) were much more likely to cross roads with low traffic volumes. One potential interpretation of this result is that bats perceive motor vehicles as a threat and exhibit avoidance behaviour whether or not the bats are in immediate danger. To test this hypothesis, we observed 211 cases of bats approaching roads that bisected their commuting routes. Information recorded at the time included the presence or absence of vehicles, the height the bat was flying, whether a bat reversed course prior to crossing the road and if so the distance from the road or vehicle (if present) when it altered its direction, and finally the speed, type and relative level of noise emitted by vehicles. Results revealed that bats were more than twice as likely to reverse course when vehicles were present as opposed to their absence. When automobiles were present 60% of bats exhibited avoidance behaviour, reversing course at an average of 10 m from a vehicle. Conversely, when no automobiles were present, only 32% of bats reversed their course and 68% crossed the road. The height a bat flew, speed of the vehicle, type of vehicle or level of noise emitted by vehicles had no effect on the likelihood of bats reversing course. These data support the hypothesis that bats perceive vehicles as a threat and display anti-predator avoidance behaviour in response to their presence.