Motorists who flash their headlights to warn fellow motorists to slow down and avoid a speeding ticket are exercising their right to free speech, says the American Civil Liberties Union (ACLU). Grain Valley, small town in Missouri, has been trying to snuff out the practice by pulling over and ticketing anyone who interferes in any way with a speed trap. The ACLU filed a federal lawsuit Tuesday seeking an injunction to put a stop to the ticketing over headlight flashing.

The case was filed in the name of Jerry L. Jarman Jr, a Kansas motorist ticketed on August 24 because he used his headlights to warn oncoming traffic of a speed trap. Such prosecutions have taken place around the country. In October, the ACLU filed a similar lawsuit in Delaware to fight back. Unlike the Delaware case, where police used a turn signal statute to outlaw headlight flashing, Grain Valley has a specific ordinance making it a crime to warn of a speed trap.

"It shall be unlawful for any person to interfere in any manner with the operation of radar or any other device or method used to check, test, gauge or determine the speed of motor vehicles within the city limits or to post any sign or notice that any speed checks are being conducted," ordinance 320.050 states.

That prohibition on speech represents more than just a clear-cut constitutional violation, the ACLU maintains. Earlier this year, a federal judge issued a injunction prohibiting the city of Ellisville from using an ordinance to outlaw headlight flashing (view case). The local prosecutor in Grain Valley quickly threw out the case against Jarman, knowing the law on the matter was legally settled.

"Defendants caused plaintiff to be pulled over, detained, cited, and prosecuted without reasonable suspicion or probable cause to believe that he had committed any crime," Missouri ACLU attorney Anthony E. Rothert wrote in Jarman's complaint. "But for [the Grain Valley police officer's] retaliatory animus regarding [Jarman's] communication, defendant Doe would not have detained plaintiff while preparing a citation."

The suit asks a federal judge to strike down the portion of the Grain Valley code prohibiting the posting of any "sign or notice" that speed traps are in use as a content-based restriction of free speech in violation of the First Amendment.