Animal detection systems are designed to detect large animals (e.g., deer (Odocoileus sp.), elk (Cervus elaphus) and/or moose (Alces alces)) as they approach the road. When an animal is detected, signs are activated that warn drivers that large animals may be on or near the road at that time. Starting in 1993, animal detection systems have been installed at over 30 locations throughout Europe and North America (see review in Huijser et al., 2006). Some of these systems have been found to be reliable and/or effective in reducing animal-vehicle collisions, whereas other efforts have been abandoned because of technical problems or changes to the road or surrounding landscape (see review in Huijser et al., 2006; Dodd & Gagnon, 2008). In order to reduce the number of animal-vehicle collisions, animal detection systems need to detect animals reliably, and they also need to influence driver behavior so that drivers can avoid a collision. Most animal detection system technologies are vulnerable to ‘false negatives’ and ‘false positives’. False negatives occur if an animal approaches, but the system fails to detect it. False positives occur if the system reports the presence of an animal, but there is no animal present. Keeping false positives and false negatives to a minimum is important as drivers are expected to respond to the warning signals. Once an animal detection system reliably detects the target species and the warning signals and signs are activated, driver response – increased driver alertness and lower vehicle speed – determines how effective the system ultimately is in avoiding or reducing animal-vehicle collisions. A higher state of alertness of the driver, lower vehicle speed, or a combination of the two can result in a reduced risk of a collision with the large animal and less severe collisions. A reduced collision risk and less severe collisions mean fewer human deaths and injuries, and lower property damage. In addition, fewer large animals are killed or injured on the road without having been restricted in their movements across the landscape and the road. Furthermore, fewer large dead animals will have to be removed, transported and disposed of by road maintenance crews. Specifically, this project aims to investigate the reliability and effectiveness of an electromagnetic animal detection and driver warning system (ADS-DWS) that was installed along U.S. 160 between Durango and Bayfield, La Plata County, Colorado.