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Research on the KRETP Rule and its application

Xiaoqiang Guo, Aimin Yang, Shumei Zhang, Lu Wang, Wei Ku, Zewei Wang

In most countries the traffic rule of keeping right is observed, multi-lane freeways often employ a rule that requires drivers to drive in the right-most lane unless they are passing another vehicle, in which case they move one lane to the left, pass, and return to their former lane. In order to know whether this rule can effectively promote a smooth traffic in both light and heavy traffic, we mainly consider four factors that are traffic flow, safety, rate of lane changing and limited speed. According to car following theory, modified and piecewise segment fixed-end-beam (FEB) model and hydrodynamic model of mixed traffic, we established highway traffic flow models. According to the deflection curve of segment fixed-end-beam, we imitate the overtaking and following process of a vehicle, stretch this process to the whole traffic flow system, imitate traffic flow by fluid motion, and then create the freeway model of traffic flow. We gain the solution to the model through the analysis of characteristic lines, the relations of flow q, designed limit speed uf, density k and rate of lane changing are showed in the following formula: q = bk + cea, where b = μ fm, c = μ fkf(1 – m), m is coefficient of wave velocity, kj is the block density if the speed is zero. We reach a conclusion that the keeping right rule except overtaking can effectively improve a smooth traffic in a light traffic, but it doesn’t in a heavy traffic. But traffic jams often happen in freeways; in this case, the keeping right rule cannot improve a smooth traffic. To enlarge traffic flow in unit road and enhance safety, we put forward a new rule of limit line and lane after the consideration of safety distance and maximum traffic. Take a four-lane freeway as an example, regulations as follows: 1) Limit line: we record the total number of vehicles running in freeways timely. When the total number reaches the maximum number N, the rule of limit line is employed in the entrances of freeways, and vehicles are not allowed to enter until the total number of vehicles is less than N. This rule can guarantee enough safety distance between vehicles. 2) Driving in different lanes: the leftmost lanes are fast lanes, which allow the driving of vehicles with a speed of 100 ~ 120 km / h. The two middle lanes are ordinary lanes, which allow the driving of vehicles with a speed of 80 ~ 100 km / h. The rightmost lanes are slow lanes, which allow the driving of vehicles with a speed of 60 ~ 80 km / h. This rule can enlarge the traffic flow of freeways