The devices used to change traffic signals are called Mobile Infrared Transmitters (MIRT), they are used by city buses and emergency vehicles to control traffic signals at intersections to allow them to pass quickly and safely. A MIRT consists of a infrared LED light array connected to a timer, the infrared LED's are mounted on the emergency light bar. When an emergency vehicle activates its overhead emergency lights the MIRT is also activated, the timer causes the LED's to strobe at a specific frequency, typically 10Hz for a low priority change like a city bus or an emergency vehicle responding at a code 2 (lights but no siren) and 14Hz for a high priority change, which would be an emergency vehicle responding at a code 3 (lights and siren). A low priority frequency will cause a normal light change, the light will go from green to yellow then red in the opposing lane before changing to green for the transmitting vehicle; a high priority frequency will immediately change the lights in both directions, the light in the opposing direction from the emergency vehicle will go straight from green to red. Some cities use specially encoded transmitters on their own unique frequency to prevent the use of homemade transmitters. In 2005 the Safe, Accountable, Flexible, Efficient Transportation Equity Act included a provision that established a minimum sentence of six months in jail for anyone illegally using a MIRT, and a minimum sentence of one year in prison for anyone selling a MIRT illegally.
The Department of Weights and Measures is a federal office, part of the National Institute of Science and Technology, that is responsible for setting and enforcing standards of metrology (the study of measurement) for goods and services. They are also responsible for ensuring that all commercial and law enforcement weighing and measuring devices are tested and inspected for accuracy, and meet Federal guidelines for specifications and tolerances. In addition to the federal office each state also has its own Department of Weights and Measures, the New York Bureau of Weights and Measures is charged with ensuring that all commercial devices used to weigh and measure commodities sold on the basis of weight, volume, or size are to be inspected and tested for accuracy at least annually. Such devices include gas pumps and vehicle, grocery and pharmacy scales. Gasoline and diesel fuels sold for use in motor vehicles are also subject to inspection to ensure they meet quality standards and are properly labeled.