Knowledge Resources

Evaluation of the BART smart parking field test revealed that the greatest technical challenges arose from the in-ground parking sensor system. The sensor system utilized had previously been used on roadways with traffic moving in one direction only. The system was modified to detect two-way vehicle movements and testing at an off-site location indicated that the sensors worked well. However, when implemented at the BART station, the sensors ability to accurately count vehicles moving at parking lot speeds was unreliable. It was later determined that the inaccuracy may have been a result of the magnetic field at the BART station, since the sensors work by detecting the changing magnetic fields from vehicles passing over the sensors. Also, sensors had difficulty accounting for atypical vehicle movements, such as cars driving into or out of the lot the wrong way.

Lessons to be learned from this experience are:

• Ensure that the sensors for the system can account for a range of parking lot vehicle movements
• Test the sensor systems on site to be sure that they conform properly to actual site conditions.

Eventually, the in-ground parking sensor system was replaced with an aboveground system. While the system was more accurate, the integration of the new sensors with the wireless counting system resulted in communication protocol problems. Researchers ultimately maintained count accuracy by using a proprietary algorithm that corrected the sensor problems and accounted for instances when vehicles queued above the sensors. In the end, the parking project managers determined that aboveground sensors were superior in providing an accurate vehicle count.

The experience of the BART field test demonstrates the unique issues associated with counting vehicles moving at parking lot speeds. In order to obtain accurate information agencies should employ sensors that can account for a range of parking lot vehicle movements. In addition, agencies should test the parking sensor systems onsite to ensure that they operate correctly under the specific site conditions.