After the 2013 Moore tornado, it became apparent that thousands of people attempt to flee major tornadoes, and this has been credited with reducing the death toll. However, during this event some people were killed as the tornado passed over the traffic jam caused by the impromptu evacuation. In addition to urban traffic, evacuation can also be hampered by flash flooding produced by associated thunderstorms, and the need to be certain about the position and direction of the tornado. Others who did not flee the Moore tornado were also killed because the buildings they were hiding in were completely destroyed, highlighting the need for storm shelters and safe rooms constructed specifically to withstand very high winds.