Roads in the US are getting more crowded and congested, and the total vehicle miles traveled (VMT) hit a record high in 2016 with 3.2 trillion miles. Congestion refers to periods when the volume of traffic exceeds the road’s capacity, think about a traffic jam where cars sit idling. All over the US, congestion is getting worse, especially in urban areas. One study found that from 1980 to 2003 the total VMT increased by 111% in urban areas, while urban lane-miles only increased by 51%, which created a net effect of heavier traffic congestion.