Abstract
Link travel speeds in road networks are essential data for a variety of research problems in logistics, transportation, and traffic management. Real-world link travel speeds are stochastic, and highly dependent on speeds in previous time periods and neighboring road links. To understand how link travel speeds vary over space and time, we uncover their distributions, their space- and/or time-dependent correlations, as well as partial correlations, based on link travel speed datasets from an urban road network and a freeway network. We find that more than 90% (57%) of travel speeds are normally distributed in the urban road (freeway) network, and that correlations generally decrease with increased distance in time and space. We also investigate if and how different types of road links affect marginal distributions and correlations. The results show that different road link types produce quite similar marginal distributions and correlations. Finally, we study marginal distributions and correlations in a freeway network. Except that the marginal distribution and time correlation are different from the urban road network, others are similar.
Highlights
Link travel speeds in road networks are essential data for a variety of research problems in logistics, transportation, and traffic management
The data collected at a location on I-35 in Austin shows that travel times tend to be normally distributed in moderate traffic conditions but lognormal under congestion[26]
The increase in distance tends to reduce the correlation of travel speeds[23,27,29], while higher congestion usually leads to higher c orrelations[27]
Summary
Link travel speeds in road networks are essential data for a variety of research problems in logistics, transportation, and traffic management. The inaccuracy in the reliability objective is 15% on average without the consideration of correlations in link travel time[16] These studies usually assume that the stochastic travel speeds obey certain c ontinuous[10,11,12,15,16,17,21] or discrete[9,14,24] distributions and have some simple[9,14,15,16] or even no correlations[10,21]. Structure plays a large role in spatiotemporal correlations in link travel speeds in a n etwork[28] These findings could be misleading since they are only based on a limited number of road links and insufficient data
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