Some crossings have pedestrian traffic signals that allow pedestrians and road traffic to use the crossing alternately. On some traffic signals, pressing a call button is required to trigger the signal. Audible or tactile signals may also be included to assist people who have poor sight. In many cities, some or most signals are equipped with countdown timers to give notice to both drivers and pedestrians the time remaining on the crossing signal. In places where there is very high pedestrian traffic, Embedded pavement flashing-light systems are used to signal traffic of pedestrian presence, or exclusive traffic signal phases for pedestrians (also known as Barnes Dances) may be used, which stop vehicular traffic in all directions at the same time.