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The main factor distinguishing police cars from others on the road is the audio and visual signals installed in them. Of the two, sirens are more effective as they can be heard much before the arrival of the vehicle at the scene of an incident. These sirens are either mechanical or electronic devices. The type that can be installed on police cars are strictly mandated by law in the USA and any deviation leads to strict fines and penalties.  Police sirens have evolved greatly over time and before you buy police siren for car , you should know more about its intricacies. The early versions of police sirens were mechanical devices that required a lot of maintenance and were not very reliable. Now, electronic sirens are used that have to be simply plugged into the car’s power unit. Various pitches and frequencies can be generated from this one device through in-built oscillators, modulators, and amplifiers. The options before a police officer are sounds ranging from a yelp to wail, hi-

Traffic signal preemption is a system that prioritizes traffic flow as per requirements through manipulation of normal traffic lights. The most common reason is controlling traffic signals in the path of an emergency vehicle so that normal traffic is regulated and it has right of way. Traffic signals are also preempted to help public transportation quickly through intersections or for regulating traffic at railroad crossings to avoid collisions.   Traffic preemption systems can be categorized as follows. • Acoustic sensors – Acoustic sensors are linked to the preemption system where a specific pattern of wails or tweets from the siren of an emergency vehicle overrides the traffic signal. The advantage here is that such a system can be easily integrated into the existing traffic signals. • Radio signals – A radio-based signal in the short-range 900MHz band uses a directional signal from an emitter to preempt traffic signals. This radio signal is not blocked by lighting,