2016 Outstanding Project of Year: Charlotte Leading Pedestrian Interval Plus (LPI+)

PROBLEM

How to enhance the comfort and safety of pedestrians using signalized crosswalks at intersections with right turn lanes without significantly affecting the capacity of the intersection?  The solution takes the idea of the leading pedestrian interval and puts it on steroids, we call it “LPI Plus”. 

 

INNOVATION

The City of Charlotte had previously installed right turn flashing yellow arrows (FYAs)at multiple locations. These FYAs were used to hold right turning traffic during leading pedestrian intervals of 5-10s. This was good but we wanted great. In March of 2015, CDOT installed 3 right turn FYAs at the intersection of Fairview Rd and Sharon Rd. There are 2 important things that make this installation innovative in providing an improved crossing environment for pedestrians.

  1. LED blankout signs with dual message displays were installed on every approach.
  2. The leading pedestrian interval was expanded to include the entire “Walk + Flashing Don’t Walk” time.

 

When a pedestrian activates a push button to cross the street, the blank out displays a “No Turn on Red” display to two different approaches. One display is to the conflicting right turn movement that will be stopped during the leading pedestrian interval with the FYA signal head. The other display is to the approach the pedestrian is crossing. This is to stop vehicles from encroaching in the crosswalk as they try to make right turns on red. The “No Turn on Red” continues to display along with a red indication for the right turn lane until the “walk + flashing don’t walk” time is completed. This gives a completely protected crossing for the pedestrian.

During the peak hours, however, the right turn volume increases to the point that it is not reasonable to hold this movement for the length of the “Walk + Flashing Don’t Walk” time period. During the peak hours the blankout signs still turn on when a pedestrian pushes the button. However, now a leading pedestrian interval of 10s is used. At the end of the 10s, the blankout sign facing the right turn vehicles changes its display to “Yield to Pedestrians” and the signal head display changes from red to flashing yellow arrow. The blankout facing the approach the pedestrian is crossing continues to display “No Turn on Red” until the pedestrian crossing has timed out.

 

SIGNIFICANCE

This significance of this is three-fold:

  1. The LPI+ concept requires a complete change in the way that we design and operate signalized intersection/pedestrian crossings. LPI+ is used to create a completely protected crossing with pushbutton activation, not just to help pedestrians enter the crosswalk. The completely protected crossing will be the normal situation and the engineer will only drop back to a leading pedestrian interval only when the effect on traffic is devastating to capacity.
  2. LPI+ creates an improved crossing environment. A fully protected crosswalk at the same time stopping vehicles from encroaching in that crosswalk is the pedestrian gold standard. This was achieved here with moderate costs, some controller database changes and slight traffic signal cabinet modifications.
  3. LPI+ can be incorporated into any new traffic signal installation. The additional cost of the blankout signs adds approximately $12,000 to the overall cost of the intersection. The modifications to cabinet and controller are a matter of implementing the ideas that the City has created. In a changing traffic engineering world where modes of travel other than the vehicle are receiving ever increasing attention, this idea moves beyond lip service and puts that emphasis on the street.

 

TRANSFERABILITY

The City is working toward making LPI+ its standard installation for all new traffic signals. We have also created a priority list for retrofits of existing intersection that uses 8 different criteria. Each signalized intersection outside of our CBD where we run fixed time has been ranked based on the criteria and the City will begin retrofitting intersections using this list in 2017.


Any municipality or State that believes in the benefits of protected crossings can institute LPI+ with relatively modest costs. Those costs can be reduced even further if there was no need to ever use a standard LPI which means that only single message blankout signs are needed. This would cut the sign costs by almost one-half.