"Speed limit enforced by aircraft" means that local law enforcement use aircraft to monitor motorists' speeds and issue citations based on radar and laser device speed measurements, according to Slate. "Speed limit enforced by aircraft" is often posted on signs in areas where police utilize this method, reports Slate.
Slate further reports that as of 2013, Virginia State Police were using aircraft for "special projects only," due to budget restraints. The Ohio State Police have been more active, with 15 uniformed police officers qualified to act as pilots, two American Eurocopter helicopters and 14 Cessna airplanes. The use of unmanned drone aircraft by law enforcement has been proposed in Houston and other areas. However, support for such a program was reported to have "collapsed" after it became clear that drones could be used to enforce traffic laws, reports the American Civil Liberties Union.