The Tampa (THEA) CV Pilot’s passive pedestrian detection system offers an alternative way to use LiDAR for traffic safety

One of the major goals of the Tampa Hillsborough Expressway Authority (THEA) Connected Vehicle (CV) Pilot is to improve pedestrian safety. At the George E. Edgecomb Hillsborough County Courthouse in downtown Tampa, there is one primary mid-block crosswalk for pedestrian access to/from the main parking garage.  Lack of attention by drivers has led to numerous vehicle-pedestrian collisions/near misses with pedestrians trying to reach or leave the courthouse. Pedestrians will also often elect to take a shortcut by crossing East Twiggs Street mid-block and outside the crosswalk, further causing concern for their safety. THEA wanted to address the pedestrian safety hazards at this location by incorporating a pedestrian detection system that would warn vehicles of pedestrians’ presence in the crosswalk into their CV-concept.

THEA originally envisioned recruiting participants to download a smartphone application that would use the device’s geolocation to provide safety alerts to nearby vehicles.  However, testing found that the geolocation data provided by the smartphone had insufficient precision to support safety applications, thus requiring THEA to look into procuring alternative pedestrian detection equipment. THEA’s procurement process began with a Requirements Specification document submitted to manufacturers of video, radar and LiDAR pedestrian detection products. THEA found that the LiDAR technology met their desired performance requirements, while the radar and video technologies did not. THEA’s eventual solution combined LiDAR equipment (to detect the pedestrians) with a CV-enabled roadside unit (to broadcast the information to CVs in the vicinity). This hybrid solution offers a twist on LiDAR’s traditional use. Typically, anti-collision systems that utilize LiDAR sensors are installed directly on the vehicle, however, THEA’s solution uses stationary LiDAR sensors mounted on posts on each end of the crosswalk.

A LiDAR sensor mounted on a postThe LiDAR units installed at the crosswalk operate by collecting high-resolution 3D representations of objects using pulsed laser light. These scans are then analyzed to identify pedestrians (as well as bicyclists) within the defined area of the crosswalk. The LiDAR is programmed to scan a small region of the sidewalk to locate pedestrians that may begin to cross. Moving pedestrians are tracked and their predicted trajectory is calculated and used to identify possible collisions based on the vehicle’s location and speed of approach.

When a pedestrian is detected in the crosswalk, the LiDAR creates a personal safety message (PSM) and sends it the Roadside Unit (RSU) that is installed near the crosswalk; the RSU then signs the PSM and broadcasts it to the Onboard Unit (OBU) of the oncoming vehicle if the vehicle’s trajectory indicates a possible collision with a pedestrian in the crosswalk. This triggers an audiovisual alert within the vehicle, where the passenger vehicle’s rearview mirror displays a symbol depicting a pedestrian in a crosswalk and a warning symbol in bright, primary colors (see Figure 2). Simultaneously, several brief audio tones are emitted within the vehicle. Due to safety issues (e.g., to avoid pedestrians being distracted), the pedestrian is neither notified nor required to take any action to trigger the alert, thus making it a passive detection system. It is the driver’s responsibility to respond to the alert by either decelerating (preferably) or swerving to evade the pedestrian. After several seconds, the visual alert disappears from the rearview mirror.

Pedistrian Warning Symbol in rearview mirror
Source THEA - Figure 2: Pedestrian Warning Symbol in the rearview mirror

THEA’s unique use of LiDAR did not come without its challenges. As the crosswalk did not have a nearby power supply for the LiDAR detectors, THEA had to work with the City of Tampa to install an electric meter. This required a lengthy permit process with the City and numerous inspections. The deployment team also experienced difficulties in getting the subterranean conduit installed for the full 120-volt electrical service that was needed for the LiDAR sensors.

The system is expected to be operational beginning in June 2019 and will be open to the public to experience the THEA Connected Vehicle Pilot as a pedestrian—just by walking downtown.