Abstract
Due to unbalanced speed-density observations, the one-regime traffic fundamental diagram and speed-density relationship models using least square method (LSM) cannot reflect actual conditions under congested/jam traffic. In that case, it is inevitable to adopt the weighted least square method (WLSM). This paper used freeway Georgia State Route 400 observation data and proposed 5 weight determination methods except the LSM to analyse 5 wellknown one-regime speed-density models to determine the best calibrating models. The results indicated that different one-regime speed-density models have different best calibrating models, for Greenberg, it was possible to find a specific weight using LSM, which is similar for Underwood and Northwestern Models, but different for that one known as 3PL model. An interesting case is the Newell's Model which fits well with two distinct calibration weights. This paper can make contribution to calibrating a more precise traffic fundamental diagram.
Highlights
The speed and density relationship determines the traffic fundamental diagram [1,2,3], so it is extremely important to analyse the speed and density relationship and this has received much attention within the past few decades
The calibrating results of five well-known single-regime models with five weight determination methods and least square method (LSM) are shown in Figure 3 and Table 3
In order to make sure which weight determination method is the best, the Relative error (RE) and root mean square error (RMSE) of five models under five weight determination methods and LSM are obtained in Figure 4 and Figure 5, respectively
Summary
The speed and density relationship determines the traffic fundamental diagram [1,2,3], so it is extremely important to analyse the speed and density relationship and this has received much attention within the past few decades. Several models including single-regime and multiple-regime ones were proposed by researchers. Though multiple-regime models are more accurate than single-regime ones, they are not suggested to be used because of lack of mathematical elegance.
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