In this paper, the speed gradient （SG） model is extended to describe the traffic flow on two-lane freeways. Terms related to lane change are added into the continuity equations and velocity dynamic equations. The em...In this paper, the speed gradient （SG） model is extended to describe the traffic flow on two-lane freeways. Terms related to lane change are added into the continuity equations and velocity dynamic equations. The empirically observed two-lane phenomena, such as lane usage inversion and lane change rate versus density, are reproduced by extended SG model. The local cluster effect is also investigated by numerical simulations.展开更多
Based on the full velocity difference model, Jiang et al. put forward the speed gradient model through the micromacro linkage （Jiang R, Wu Q S and Zhu Z J 2001 Chin. Sci. Bull 46 345 and Jiang R, Wu Q S and Zhu Z J 2...Based on the full velocity difference model, Jiang et al. put forward the speed gradient model through the micromacro linkage （Jiang R, Wu Q S and Zhu Z J 2001 Chin. Sci. Bull 46 345 and Jiang R, Wu Q S and Zhu Z J 2002 Trans. Res. B 36 405）. In this paper, the Taylor expansion is adopted to modify the model. The backward travel problem is overcome by our model, which exists in many higher-order continuum models. The neutral stability condition of the model is obtained through the linear stability analysis. Nonlinear analysis shows clearly that the density fluctuation in traffic flow leads to a variety of density waves. Moreover, the Korteweg-de Vries-Burgers （KdV-Burgers） equation is derived to describe the traffic flow near the neutral stability line and the corresponding solution for traffic density wave is derived. The numerical simulation is carried out to investigate the local cluster effects. The results are consistent with the realistic traffic flow and also further verify the results of nonlinear analysis.展开更多
This paper covers why measurements at various speeds with CFME （continuous friction measurement equipment） are not able to measure the speed-friction gradient of the pavement as determined by the macro-textural feat...This paper covers why measurements at various speeds with CFME （continuous friction measurement equipment） are not able to measure the speed-friction gradient of the pavement as determined by the macro-textural features of the surface. Most CFMEs measure friction in the slip ratio range of 10% to 18%. In this range, it is shown that the friction versus slip speed of these devices are mainly determined by the coupled properties of the surface micro-texture and relevant tire properties and to a minimal extent only by pavement macro-texture properties. The determinacy of low slip ratio friction measurements on the macro-textural features of the pavement surface are shown to be so low that they are inadequate to capture macro-texture caused speed degradation of friction. It is also shown in the paper that close to 100% slip ratio measurements at a relatively wide speed scale or direct macro texture measurements are needed to adequately determine the speed gradient if friction caused by the pavement macro-texture. The data and analysis in this paper provide strong and compelling evidence that the EFI （European Friction Index） or EFI developed by the HERMES （Harmonization of European Routine and Research Measuring Equipment for Skid Resistance） project sponsored by FEHRL （Forum of European National Highway Research Laboratories） is strongly affected by the lack of consideration of this phenomenon. It is recommended that the results of the HERMES project are reviewed taking into account the findings of the present paper. Based on the results of the presented paper it is suggested that CFME＇s only measure friction at a fixed speed with a standard tire and use a macro-texture measuring device to obtain the pavement speed gradient.展开更多
文摘In this paper, the speed gradient （SG） model is extended to describe the traffic flow on two-lane freeways. Terms related to lane change are added into the continuity equations and velocity dynamic equations. The empirically observed two-lane phenomena, such as lane usage inversion and lane change rate versus density, are reproduced by extended SG model. The local cluster effect is also investigated by numerical simulations.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11072117 and 61074142)the Scientific Research Fund of Zhejiang Provincial Education Department,China (Grant No. Z201119278)+1 种基金the Natural Science Foundation of Ningbo City,China (Grant Nos. 2012A610152 and 2012A610038)the K. C. Wong Magna Fund in Ningbo University,China
文摘Based on the full velocity difference model, Jiang et al. put forward the speed gradient model through the micromacro linkage （Jiang R, Wu Q S and Zhu Z J 2001 Chin. Sci. Bull 46 345 and Jiang R, Wu Q S and Zhu Z J 2002 Trans. Res. B 36 405）. In this paper, the Taylor expansion is adopted to modify the model. The backward travel problem is overcome by our model, which exists in many higher-order continuum models. The neutral stability condition of the model is obtained through the linear stability analysis. Nonlinear analysis shows clearly that the density fluctuation in traffic flow leads to a variety of density waves. Moreover, the Korteweg-de Vries-Burgers （KdV-Burgers） equation is derived to describe the traffic flow near the neutral stability line and the corresponding solution for traffic density wave is derived. The numerical simulation is carried out to investigate the local cluster effects. The results are consistent with the realistic traffic flow and also further verify the results of nonlinear analysis.
文摘This paper covers why measurements at various speeds with CFME （continuous friction measurement equipment） are not able to measure the speed-friction gradient of the pavement as determined by the macro-textural features of the surface. Most CFMEs measure friction in the slip ratio range of 10% to 18%. In this range, it is shown that the friction versus slip speed of these devices are mainly determined by the coupled properties of the surface micro-texture and relevant tire properties and to a minimal extent only by pavement macro-texture properties. The determinacy of low slip ratio friction measurements on the macro-textural features of the pavement surface are shown to be so low that they are inadequate to capture macro-texture caused speed degradation of friction. It is also shown in the paper that close to 100% slip ratio measurements at a relatively wide speed scale or direct macro texture measurements are needed to adequately determine the speed gradient if friction caused by the pavement macro-texture. The data and analysis in this paper provide strong and compelling evidence that the EFI （European Friction Index） or EFI developed by the HERMES （Harmonization of European Routine and Research Measuring Equipment for Skid Resistance） project sponsored by FEHRL （Forum of European National Highway Research Laboratories） is strongly affected by the lack of consideration of this phenomenon. It is recommended that the results of the HERMES project are reviewed taking into account the findings of the present paper. Based on the results of the presented paper it is suggested that CFME＇s only measure friction at a fixed speed with a standard tire and use a macro-texture measuring device to obtain the pavement speed gradient.
