Road network circuity in metropolitan areas

Circuity, the ratio of network to Euclidean distances, describes the directness of trips and the efficiency of transportation networks. This paper measures the circuity of the fifty-one most populated Metropolitan Statistical Areas (MSAs) in the United States and identifies trends in those circuities between 1990 and 2010. Overall circuity has increased between 1990 and 2010: random points have not only become farther apart in distance, their shortest network path has become more circuitous, suggesting that the more recently constructed parts of street networks are laid out more circuitously than older parts of the network. Over this period thirty-five MSAs experienced a statistically significant increase in circuity (six experienced a significant decrease). As expected, short trips are more circuitous than long trips. A new circuity distance-decay function describes how circuity varies with distance within metropolitan areas. The parameters of this function have changed from 1990 to 2010.