A Reduced Phase Intersection (RPI), (which has also been labeled as Continuous flow intersection (CFI) or crossover/displaced left-turn (XDL)), is an at-grade intersection design which relocates the left turning vehicles from the conflicting with the through vehicle movements. The same number of lanes are provided, but they are rearranged so that a separate left turn signal phase is no longer needed. This design therefore reallocates available signal timing more efficiently.
A RPI design is currently under construction on Camellia and Guilbeau at its intersection with Johnston St. A simulation of the new intersection can be viewed by clicking on the following link:
Click here to view Camellia looking toward Guilbeau Rd. at Johnston St. (Large File: Windows Media 252MB).
Click here to view Camellia looking toward Guilbeau Rd. at Johnston St. (Flash).
Traffic traveling on Camellia and Guilbeau, who wish to turn left will do so some 200 feet prior to Johnston. Adequate signing, signals, and lane channelization will almost make it transparent to the typical driver. It is perceived the driver using this new design will not notice any real difference when driving through this intersection, other than a reduction in overall vehicle delay. When the light turns green for Camellia / Johnston, all through and left turn traffic lanes, a total of 8 lanes, will move at the same time, rather than a maximum of only 4 lanes as a conventional intersection design.
Significant vehicle delays at conventional intersection with high traffic volumes is due to the required time for a relatively small number of left-turn vehicles because the through movements which are much larger in numbers must for the left turn signal phase.
Additionally, because left turn movements no longer conflict with through traffic movements, a reduction in these types of traffic crashes is also expected.