Turbo-Roundabout: Case Study of Driver Behavior and Kinematic Parameters of Light and Heavy Vehicles

This research compared kinematic and behavior parameters of light and heavy vehicles at turbo-roundabouts. This is of interest because heavy vehicles can influence turbo-roundabout functionality more than that of conventional roundabouts. The traffic arrival process at arms of a typical turbo-roundabout was studied. Using image-processing techniques, the trajectories of about 1,400 light vehicles and 300 heavy vehicles were examined at a roundabout entry, on the ring, and at the roundabout exit. Light vehicles had moderate average speeds lower than $25\mathrm{km}/\mathrm{h}$ at the entry lanes, 15 m prior of the yield line, whereas heavy vehicles had an average speed of about $20\mathrm{km}/\mathrm{h}$ on the same section. Significant differences were found in average acceleration: they were generally below $2\mathrm{m}/{\mathrm{s}}^2$ on arm lanes and $1.5\mathrm{m}/{\mathrm{s}}^2$ on circulating lanes for light vehicles, whereas those of heavy vehicles were $0.5\mathrm{m}/{\mathrm{s}}^2$, much lower than the corresponding acceleration values of light vehicles. The values of the critical gap $t_c$ and follow-up time $t_f$ estimated for light vehicles ranged between $t_c=4.03-5.48\mathrm{s}$ and $t_f=2.52–2.71\mathrm{s}$ respectively, whereas heavy vehicles had $t_c$ and $t_f$ values 15%–47% higher than those of light vehicles.