This book explores current and emerging vehicle-based technologies that can detect driver blood alcohol concentration (BAC) and monitor driver impairment due to alcohol. Detection technologies have the potential to prevent death and injury by monitoring BAC and/or driving performance for signs of impairment, and if necessary either prevent ignition or take other actions to prevent a crash. This book assesses the capability of existing and anticipated technologies to detect and prevent alcohol-impaired driving. It also includes a concept of operations to describe how to implement technology-based countermeasures while addressing concerns such as privacy, public acceptance, and legal issues.