| Title |
Determining Ideal Distance between Consecutive Exit Ramps |
| Keywords |
road geometry;exit ramp;perception-reaction time;decision Sight distance;lane-changing time;도로 기하구조;유출램프;인지반응시간;판단시거;차로변경 |
| Abstract |
When an expressway intersects another expressway, a unique connector needs to be designed between the two consecutive exit ramps. Tn such a case, it is important to design a connector such that there is enough distance for drivers to find their way safely. A current design manual in Korea prescribes the minimum length of the connector as 240 m. In this research, we have suggested a method for calculating the minimum length of a connector in order to check the feasibility of the currently prescribed length. For this purpose, we have attempted to determine the total perception-reaction time and lane-changing time required by a driver. For determining the driver"s perception-reaction time, we have used the driver"s decision time in addition to the conventional 2.5 s of perception-reaction time for stopping sight distances. We have considered both the design speed and the average travel speed for the calculation of the length. To evaluate the accuracy of the new method, we have chosen four sites on expressways for which relatively high accident rates were recorded. As a result, we could verify that the current limit (240 m) was sufficient for drivers to be able to change lanes in the given specific geometry. However, the prescribed limit should be revised in case the drivers" decision time is considered to be their perception-reaction time. All new approaches for calculating the ideal length of a connector have been carried out by taking into account the design speed as well as the average travel speed. Owing to the characteristics of the specific geometry for two consecutive exit ramps and the large difference between the design speed and the average travel speed in the objective areas, it is more realistic to use the proposed method by keeping the decision time equal to a driver"s perception-reaction time, in order to determine the ideal distance that should be maintained between two consecutive exit ramps. |