Analysis on Usage Comfort of Highway Alignment Quality Based on a_y and a_y's Change Rate

To control a_y and a_y's rate of growth is always an important part in road geometric design. At present, however, vehicles are simplified as single rigid body when a_y and da_y/dt are calculated. Moreover, the calculation is made in two-dimensional plane, which does not comply with the actuality. In this article, a "Road-Driver-Vehicle" simulation system (RDVS) is applied to get a_y and da_y/dt. In RDVS, the dynamic vehicle model is driven on three-dimensional roads under the control of driver model, so it is more close to the real driving. We chose three roads in the mountainous area of southwestern China as the experiment subjects with designed speed of 20, 60 and 100 km/h, respectively. The results show: a_y gotten from RDVS is bigger than that from single rigid body calculation. As RDVS is more reliable, a_y from single rigid body calculation may cause an insufficient estimation. Suppose the driver drives at the designed speed. Though the designed speed varies, the peak value of a_y of the three objects range in [2.0m/s², 2.5m/s²], beyond the limit of comfort but within tolerate scope. As for Subject C, without application of clothoid, da_y/dt will exceed the limit of 1.0m/s³. So, it is suggested using clothoid, considering improving the quality.