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Fig.5.1.2.three phase of overtaking process

5.1.2 Numerical simulation results and discussion

In order to facilitate the subsequent discussions, we define the space occupation rate asp?(NCAR?3?Ntruck)/3?L, whereNCAR indicates the number of small vehicles on the driveway,Ntruck indicates the number of trucks and buses on the driveway, and L indicates the total length of the road. The vehicle flow volume Q is the number of vehicles passing a fixed point per unit time,Q?NT/T, where NTis the number of vehicles observed in time durationT.The average speed Va?(1/N?T)?1?1vit, vitis the speed of vehicle i at time t. Take overtaking ratio pfas the evaluation indicator of the safety of traffic flow, which is the ratio of the total number of overtaking and the number of vehicles observed. After 20,000 evolution steps, and averaging the last 2000 steps based on time, we have obtained the following experimental results. In order to eliminate the effect of randomicity, we take the systemic average of 20 samples [5].

? Overtaking ratio of different control rule conditions

Because different control conditions of road will produce different overtaking ratio, so we first observe relationships among vehicle density, proportion of large vehicles and overtaking ratio under different control conditions.

Ti

(a) Based on passing lane control (b) Based on speed control

Fig.5.1.3

Fig.5.1.3 Relationships among vehicle density, proportion of large vehicles and overtaking ratio under different

control conditions.

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It can be seen from Fig. 5.1.3:

(1) when the vehicle density is less than 0.05, the overtaking ratio will continue to rise with the increase of vehicle density; when the vehicle density is larger than 0.05, the overtaking ratio will decrease with the increase of vehicle density; when density is greater than 0.12, due to the crowding, it will become difficult to overtake, so the overtaking ratio is almost 0.

(2) when the proportion of large vehicles is less than 0.5, the overtaking ratio will rise with the increase of large vehicles; when the proportion of large vehicles is about 0.5, the overtaking ratio will reach its peak value; when the proportion of large vehicles is larger than 0.5, the overtaking ratio will decrease with the increase of large vehicles, especially under lane-based control condition s the decline is very clear.

? Concrete impact of under different control rules on overtaking ratio

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Fig.5.1.4

Fig.5.1.4 Relationships among vehicle density, proportion of large vehicles and overtaking ratio under

different control conditions. (Figures in left-hand indicate the passing lane control, figures in right-hand indicate the speed control.

Pf1 is the overtaking ratio of small vehicles over large vehicles, Pf2 is the overtaking ratio of

Pf3 is the overtaking ratio of large vehicles over small vehicles, Pf4 is the

small vehicles over small vehicles,

overtaking ratio of large vehicles over large vehicles.).

It can be seen from Fig. 5.1.4:

(1) The overtaking ratio of small vehicles over large vehicles under passing lane control is much higher than that under speed control condition, which is because, under passing lane control condition, high-speed small vehicles have to surpass low-speed large vehicles by the passing lane, while under speed control condition, small vehicles are designed to travel on the high-speed lane, there is no low- speed vehicle in front, thus there is no need to overtake. (2) The overtaking ratio of small vehicles over small vehicles under speed control condition is much higher than that under passing lane control condition.

(3) The overtaking ratio of large vehicles over small vehicles under passing lane control condition is much higher than that under speed control condition.

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(4) The overtaking ratio of large vehicles over large vehicles under passing lane control condition is much higher than that under speed control condition. ? Impact of different control rules on vehicle speed

Fig. 5.1.5 Relationships among vehicle density, proportion of large vehicles and average speed under

different control conditions. (Figures in left-hand indicates passing lane control, figures in right-hand indicates speed control.

Xa is the average speed of all the vehicles, Xa1 is the average speed of all the small vehicles, Xa2 is

the average speed of all the buses and trucks.).