Using travel diary data from 2000-2001 and 2010-2012 this research examines fundamental traffic relationships at the metropolitan level. The results of this paper can help to explain the causes of some traffic phenomena. Network average speed by time of day can be explained by trip length and cumulative number of vehicles on the road. A clockwise hysteresis loop is found in the Metropolitan Fundamental Diagram in the morning period and a reverse process happens in the afternoon.
Wang, K., & Levinson, D. M. (2016). Towards a metropolitan fundamental diagram using travel survey data. PLoS ONE, 11(2). https://doi.org/10.1371/journal.pone.0148660