Heavy duty vehicles (HDVs) like buses have poor fuel consumption efficiency due to their heavy curb weight and sizes as a result of stop-and-go traffic in the vicinity of signalized intersections. This study developed a Green Light Optimal Speed Advisory system for buses (B-GLOSA) that consisted of an easy-to-calibrate fuel consumption model that could compute instantaneous diesel bus fuel consumption rates. The system was implemented on diesel buses and the performance of B-GLOSA was validated through field tests conducted with 30 participants on a connected vehicle test bed in Virginia. The performance of the B-GLOSA system was evaluated only under light-traffic conditions as vehicles were suggested to completely stop under highly congested traffic conditions. The main aim of the study was to improve the energy efficiency of buses by reducing the stop-and-go maneuvers in the vicinity of signalized intersections within the range of a dedicated short-range communication (DSRC) or Direct Cellular Vehicle to Everything (C-V2X) system.
B-GLOSA is a bus eco-driving system that computes fuel efficient trajectory of buses using traffic signal data received from downstream signalized intersections. It is formed as an optimization problem using a bus fuel consumption model, a vehicle dynamics model, traffic signal timings and the relationship between vehicle speed and distance to the intersection, and is solved by dynamic program with a path search algorithm. During the field tests, 30 participants drove through three scenarios listed as follows:
- Base case uninformed drive
- An informed drive with signal timing information communicated to the driver
- An informed drive with the recommended speed computed by the B-GLOSA system.
A raw dataset comprising of 1440 sets of trip information across these three test scenarios were collected and further analyzed to test the system performance in the field tests. Different experimental design approaches were considered to evaluate the impact of three factors (scenario, road grade, and red-indication offset) on fuel consumption level and travel time using the data collected.
- A quantitative analysis of the test results indicated that the B-GLOSA system can significantly smoothen the bus trajectory while traversing a signalized intersection, and simultaneously save fuel consumption and travel times.
- Fuel Consumption: Scenario-3 saved 22.1 percent of overall average fuel consumption, compared with Scenario-1, and Scenario-2 saved 9.7 percent of overall fuel consumption.
- Compared to uninformed drive (Scenario-1) the average fuel consumption under informed drive with the aid signal timing information (Scenario-2) was 13.4 percent and 6 percent less for downhill and uphill directions, respectively.
- In Scenario-3, the average fuel consumption with B-GLOSA was 34.2 percent and 10.1 percent less for downhill and uphill directions, compared to the uninformed drive case.
- Travel time: Scenario-3 reduced 6.1 percent of overall average travel time compared with Scenario-1, and Scenario-2 reduced 2.8 percent of overall travel time.
- Compared to uninformed drive (Scenario-1), the average travel times under informed drive with the aid signal timing information (Scenario-2) was 2.5 percent and 3.0 percent less for downhill and uphill directions, respectively.
- In Scenario-3, the average travel times with B-GLOSA was 6.9 percent and 5.3 percent less for downhill and uphill directions, respectively.