Leading Pedestrian Interval (LPI) is a signal timing adjustment that gives pedestrians a head start before drivers are allowed to enter the intersection.  LPI allows pedestrians to enter the crosswalk at an intersection 3-7 seconds before vehicles are given a green indication, establishing the pedestrians’ presence in the crosswalk before vehicles have priority to turn right or left.

LPI is deployed as the standard at all Cary traffic signals that have pedestrian signal heads and push buttons.

Click here to read more from the FHWA on how LPI can improve pedestrian safety.

Response to 911 calls has become faster and safer through a program to put traffic signal control in the hands of emergency responders.  Cary Transportation and Public Works Departments collaborated with Fire and NCDOT to install emergency vehicle preemption devices at signals where they can be beneficial in reducing emergency response times.

The emergency vehicles communicate with the signal-mounted devices (see photo) to interrupt the normal signal timing (preemption) and provide green lights to the emergency vehicle along their route to the emergency.  Cary is also testing this technology on GoCary buses to improve the reliability of our transit system.

Accessible Pedestrian Signals (APS) are components of the traffic signal that provide information in non-visual formats (audible or tactile) for pedestrians with vision disabilities.  A typical APS includes an audible tone to help locate the push button, tactile markings to orient the pedestrian, vibratory feedback, and speech messages.  The intent of APS is to provide the same information to visually-impaired pedestrians as is provided in the more traditional manner.  For example, when the “WALK” sign is illuminated, a message is broadcast “walk sign is on”.

Cary has committed to providing APS at all new signals with pedestrian facilities on Cary-maintained roads.

Flashing yellow arrow turn signals are installed at many Cary intersections and are intended to improve both the efficiency of the signal during off-peak hours and the safety of the intersection by more clearly indicating a yield condition to drivers.

Flashing left and right turn arrows provide clearer instructions to drivers that they have to yield to oncoming traffic and pedestrians.  During higher volume periods (morning and evening rush hours) when there aren’t sufficient gaps for a “permissive” turn, the flashing arrow can be replaced with a solid green “protected” phase arrow.

Click here to read NCDOT’s safety study for Flashing Yellow Arrow signals.

The Dynamic Left Turn intersection (DLTi) is an intersection configuration proposed and implemented by NCDOT to improve traffic flow at one of the state-maintained intersections connected to Cary’s ATMS.  The configuration varies the number of available left-turn lanes, using a pair of LED-powered overhead signal panels that activate or deactivate the rightmost left-turn lane, depending on the time of day and traffic conditions.

Both left-turn lanes are active during high volume periods (rush hour) and display a green arrow.  During less busy times (non-rush hour), the rightmost left-turn lane can deactivate, allowing drivers in the remaining left-turn lane to receive a flashing yellow arrow indication (more info on that above).  The lanes are activated and deactivated using a pair of overhead signal panels that display either a white left-turn arrow or a red “X”.

Click here to read more from the Regional Transportation Alliance (RTA) and to watch a video from NCDOT on how a DLTi operates.

Here is a quick infographic from NCDOT as well.