The main purpose of this study is to search a method for reducing traffic accident at signalized intersections. One of the important factors for this is the Left-turn phase sequence. There are several alternatives for left-turn signal controls like Le...
The main purpose of this study is to search a method for reducing traffic accident at signalized intersections. One of the important factors for this is the Left-turn phase sequence. There are several alternatives for left-turn signal controls like Leading left-turn, Lagging left-turn, Separate left-turn, Combination of Leading and Lagging left-turn, PPLT(Protection-Permissive left turn).
In 1985, the operational principle of Left-turn phase Sequence was changed from Lagging left-turn to Leading left-turn in Korea. Then there was a resonable motive - no exclusive left turn - lane and narrow intersection.
Now, it is necessary to evaluate the performance difference between Leading and Lagging left-turn phase Sequence.
The process of this study is as follows :
- First, all the intersection was divided three parts for analysis the traffic safety : Inside part of an Intersection, Crosswalk, Intersection approach and exit.
- Second, a safety analysis was performed by using the concepts of "Effective Interphase Period(EIP)" and "Conflict method".
The study results are summerized as follows :
1. The number of traffic accident between Left-turn vehicle and opposing through vehicle at inside intersection increase about 20% when phase Sequence was changed from Leading to Lagging left-turn sequence based on the EIP.
2. The number of traffic accident(between car and pedestrian) at Crosswalk decrease about 50% at Lagging left-turn Sequence because of the number and period of Conflicts.
3. The number of traffic accidents at intersection approach decreased about 33% at Lagging left-turn Sequence because of the stop rate.
4. It is concluded that Lagging left-turn phase may be superior to Leading left-turn phase, because Lagging phase reduces the total traffic accidents at intersection about 11.5%.
5. The benefit of phase Sequence changes from Leading to Lagging phase were significant. For an example the Accident cost will reduced about 41.8 billion won per year in korea.
The Lagging phase Sequence is strongly recommended for the below cases:
1. An intersection that has many pedestrian accident because of the heavy pedestrian traffic.
2. An intersection that has many rear-end accident happen at the intersection approach.
3. An intersection that has frequent spill back situations because of the phase Sequence.
4. Especially for isolated and diamond shaped intersections.