@article{ref1,
title="On the fundamental diagram for freeway traffic: A novel calibration approach for single-regime models",
journal="Transportation research part B: methodological",
year="2015",
author="Qu, Xiaobo and Wang, Shuaian and Zhang, Jin",
volume="73",
number="",
pages="91-102",
abstract="The speed-density or flow-density relationship has been considered as the foundation of traffic flow theory. Existing single-regime models calibrated by the least square method (LSM) could not fit the empirical data consistently well both in light-traffic/free-flow conditions and congested/jam conditions. In this paper, first, we point out that the inaccuracy of single-regime models is not caused solely by their functional forms, but also by the sample selection bias. Second, we apply a weighted least square method (WLSM) that addresses the sample selection bias problem. The calibration results for six well-known single-regime models using the WLSM fit the empirical data reasonably well both in light-traffic/free-flow conditions and congested/jam conditions. Third, we conduct a theoretical investigation that reveals the deficiency associated with the LSM is because the expected value of speed (or a function of it) is nonlinear with regard to the density (or a function of it).<p />",
language="en",
issn="0191-2615",
doi="10.1016/j.trb.2015.01.001",
url="http://dx.doi.org/10.1016/j.trb.2015.01.001"
}