## 4 Effect of Moving Bottlenecks on the Contraflow Lane
### Effect of Truck Moving Bottlenecks
#### 4.2.1 Development and Calibration of the Vissim Model  
To achieve realistic simulations and enable comparison, the Vissim model was developed using the results of the present Xihan Highway field experiments under regular and contraflow conditions. The road, vehicle, traffic input, driver models, and simulation cycles were developed, and the parameters of each model were reset and corrected. Road model: The geographical map of the area of the experimental road was first imported into Vissim, and a dual four-lane highway with a contraflow lane was created. The width of each lane was 3.5 m and the length of the contraflow lane was 13.3 km. Vehicle model: Based on the traffic data obtained from the field experiments, three passenger car models were built, measuring 4.0 \(\times\) 2.0, 4.2 \(\times\) 2.0, and 4.4 \(\times\) 2.0 m, respectively. According to the 2-year statistics obtained by the highway toll station, two truck models were also built, and their technical parameters used in Vissim are listed in Table 2.  
Figure 4: Speed change with respect to the coach ratio in field experiments. Traffic input model: Different schemes were developed using five different truck ratios (0%, 10%, 20%, 30%, and 40%) and three traffic flow volumes (2000, 2500, and 3000 veh/h). It should be noted that the traffic flow volume was measured using the passenger car equivalence. The average speed with contraflow was considered as the effectiveness measure of the scheme. Driver model: The expected speeds of the passenger cars and trucks were 50-80 and 40-70 km/h, respectively. The stopping distance (CC0), time headway (CC1), car-following variable (CC2), threshold distance of the car-following state (CC3), threshold distance of the positive/negative car-following state (CC4/CC5), and the number of observed vehicles were tested by sensitivity analysis of the traffic data obtained from the Vissim simulations. The results showed that only CC0, CC1, and CC2 impacted the Vissim simulations. The other parameters of the driver model were thus set to the system default values. To determine the optimal combination of CC0, CC1, and CC2, a multifactor orthogonal test was conducted to identify the factor level that produced the minimum difference between the Vissim simulations and the field experiments. Based on the result of the test, CC0, CC1, and CC2 were set to 1.5 m, 1.2 s/vehicle, and 4 m, respectively. Simulation cycle: Four traffic scenarios with truck control and contraflow were examined to minimize the effect of truck moving bottlenecks. Each scenario, with its traffic flow volume, truck ratio, and traffic scheme was simulated five times and the observed parameters were averaged. In total, 300 simulations were conducted. Since the traffic flow required some time to stabilize after a simulation was commenced, only the simulation cycles between 600 and 4200 s were collected to ensure reliability. The four considered truck control traffic schemes were as follows:  
* No Restriction (NR) Trucks were allowed to drive on any lane, including the contraflow lane. * No Trucks (NT) Trucks were forbidden from the highway. * No Trucks in the Contraflow Lane (NC) Trucks were forbidden from crossing the median and entering the contraflow lane. This was because their size and weight made lane changing and passing through the median difficult. This scheme was aimed at saving travel time and increasing the overall traffic flow speed. * Truck Lane (TL) The right-most normal lane was designated as the TL and used by only trucks, and trucks could only travel on this lane. This eliminated interweaving between passenger cars and trucks and significantly reduced the number of vehicle platoons. The calibration of the Vissim simulation model was assessed by the Geoffrey E. Havers (GEH) statistic to compare the difference between the simulations and field experiments. The GEH statistic value for the calibration of simulation models should be \(<\)5 for at least 85% of the volume check points.