The increasing concern towards urban noise pollution and present law-enforcement technique shortcomings highlight the need for an automated, cost-effective, and efficient solution. We built automated, stand-alone system prototype to deploy on overhead bridges for single-lane monitoring on expressways. Every vehicle in the monitored lane is scrutinized for tailpipe emission noise, and if a violation is found, the system triggers an onboard camera to capture the vehicle license plate number. The gathered evidence includes audio and video, a picture of the vehicle’s license plate, and log files containing SPL values with date and time stamps. Authorities use the gathered-evidence report to issue an inspection notice to the suspected vehicle for possible illegal modification.