Power in the wrong hands: devices for changing a red light to green are great for officials responding to an emergency. But now the technology is available to anyone with $1,500.

To any motorist who has ever been stuck at a red light, it may seem like the perfect dream. You pull up to the intersection, you hit a magic button, the light turns green, and you go on your way. No traffic backups, no long frustrating waits, easier commutes, everyone benefits.

The truth is buttons that change red lights to green are not only real, they are widely employed by state and local governments. They are "signal preemption devices," the most common form of which is a mobile infrared transmitter (MIRT). When activated, a MIRT emits a coded frequency to a receiver in the traffic light that instructs the light to either remain green or change to green for the oncoming vehicle. The signal also changes the light to red for all other directions.

For law enforcement officers, fire departments and medical personnel, this control can dramatically improve emergency response. Signal preemption allows responders to move safely through busy intersections and save valuable time on their way to incidents. In emergency situations, even a few minutes can determine whether a criminal is caught, a building burns down or a life is saved. A survey by the U.S. Department of Transportation in 2002 found that in the 78 largest cities in the United States, 381 transportation agencies had equipped almost 27,000 intersections with signal preemption capability.

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Although signal preemption has many benefits, state and local officials are increasingly alarmed about the public use of the technology. MIRTs are now widely available for sale on the Internet and can be used by anyone willing to pay $1,500. At a minimum, officials can envision chaotic situations at intersections with multiple MIRT equipped vehicles vying for signal control. A more significant and dangerous concern, however, is the potential for interference with emergency response vehicles that could jeopardize lives and threaten property.

Lawmakers are responding by prohibiting interferences with traffic signals or the use of MIRTs by anyone other than emergency personnel.

Illinois' new law specifically prohibits the use of signal preemption by unauthorized motorists. In 2004, legislators in at least 25 other states considered similar legislation. As of the end of July, measures had passed in Alaska, Delaware, Georgia, Illinois, Kansas, Louisiana, Maine, Michigan, New Hampshire, Oklahoma, Rhode Island, South Dakota, Utah, Virginia and West Virginia. Bills were still pending in 11 other states at press time.

"We had to recognize that technology had outstripped the code," says Delegate Robert Bell, who co-sponsored legislation to prohibit the unauthorized use of MIRTs in Virginia. "We had already prohibited radar detectors, it made sense to prohibit these too."

Matt Sundeen tracks the use of technology in motor vehicles for NCSL.