Despite a growing body of evidence worldwide that bats are affected by roads, there has been little research into the effects of traffic volume on bat activity. In New Zealand, there is considerable uncertainty over whether, or to what extent, roads affect New Zealand's endemic bat populations, and this has resulted in uncertainty during the planning and consent phases of road development projects. This research investigated whether Chalinolobus tuberculatus (long-tailed bat) activity correlates with night-time traffic volume on New Zealand's highways. Bat activity was monitored at 57 traffic monitoring sites throughout New Zealand using pairs of bat detectors, with one placed beside the highway (highway) and one placed ≥ 200 metres from the highway (distant). Generalised linear mixed effects models were used to investigate the relationship between bat detections, position in relation to the highway, and various measures of traffic volume. The model that best explained the variation in bat detections was the interaction effect between bat detector position (highway, distant) and night-time traffic volume (volume). Outputs from this model show a negative relationship between bat activity and night-time traffic volume for highway bat detector units, while distant bat detector units had no discernible relationship with night-time traffic volume. These results indicate that night-time traffic volume affects the use of roads by bats, i.e. when overnight traffic increased, the probability of detecting bats decreased. Whether or to what extent this will affect the long-term viability of New Zealand's C. tuberculatus populations is a high priority for further investigation.