DGPS system augmentation for lane assist in urban areas

Twin Cities Metro Transit operates express bus service on certified road shoulders during periods of high congestion (i.e., during "rush hour"), improving customer satisfaction and on-time schedule adherence. More than 200 miles of bus-only shoulders have been certified in the Twin Cities area. These shoulders are predominately located in suburban areas which provide clear views of the sky above. Typical operating conditions place a bus that is 2.97 meters (9.75 feet) wide on a shoulder 3.05 meters (10 feet) wide, which gives a driver very little room for error. To assist a driver with the lane keeping task, particularly under poor weather conditions which make it difficult for a driver to determine the edges of the shoulder, a lane assist system has been designed and tested. This system uses dual frequency, carrier-phase DGPS and an on-board geospatial database for lane positioning, radar and lidar sensors for collision avoidance, and graphical, tactile, and haptic interfaces to provide advisories and warnings to a driver. Providing lane assistance to a driver in urban areas where both DGPS availability and accuracy are low due to a combination of satellite signal blockage (urban canyons) or multipath has motivated a new technique for providing accurate vehicle position and heading estimates. This new technique uses RFID and laser scanner technology to accurately determine both vehicle position and heading for a dedicated lane of travel. This paper describes both the RFID and laser scanner approaches to vehicle positioning and how the RFID and laser scanner information will be integrated to provide vehicle positioning and heading information which is functionally equivalent to DGPS information for the lane assist application. The system components described herein will be integrated and demonstrated on a transit bus operating on an exclusive busway in downtown Minneapolis, MN, by July, 2008.