The Multipath Signal Phase and Timing (SPAT) Broadcast Project demonstrated the Safe Green Passage traffic signal application, which provides speed guidance to an approaching driver so that a vehicle may safely pass through the green phase of an upcoming traffic signal. This is accomplished by the signal system’s ability to send SPAT information to approaching vehicles even when they are several miles or multiple signals away. The simulation performed to evaluate performance of the Safe Green Passage application used three intersections along Grand River in Novi, Michigan (Drake Road, Halstead Road, and an M-5 exit ramp). This site was chosen because accurate signal timing information was available. Field testing of the application occurred at two signalized intersections in Oakland County, Michigan.
- Identify areas with poor cellular signals. Even though the cellular signal was adequate for the field test, better reception would be needed for a larger deployment.
- Consider line-of-sight design constraints. Early field testing of dedicated short-range communications (DSRC) technology was challenging because of the limitations the radios had when transmitting and receiving data. Trees interfered with DSRC radio signals.
- Consider the effects of driver behavior. There may be a limited speed-range window in which a driver will have freedom to maneuver in traffic and comply with recommended intersection approach speeds.