Research Spotlight: Eco-Speed Control for Diesel and Hybrid Electric Buses in the Vicinity of Signalized Intersections

Researchers at Virginia Tech (VT) and Morgan State University (MSU) are taking a serious look at reducing vehicle fuel consumption and emissions by studying some of the largest vehicles on the roads – conventional diesel and hybrid electric buses. Building on their previous research that developed an Eco-Speed Control (ESC) system to reduce fuel consumption levels for vehicles with conventional engines, the team is turning its attention to fuel savings associated with integrating buses with ESC technology.

Communication between a traffic signal controller and a vehicle equipped with a global positioning system (GPS) and communication hardware provides the VT-developed ESP system with sufficient information (vehicle position, vehicle speed and signal phasing and timing data) to compute the fuel efficient speeds. Hesham Rakha, Ph.D., P.Eng. Samuel Reynolds Pritchard Professor of Engineering in the Charles E. Via, Jr. department of civil and environmental engineering at VT and director of the Center for Sustainable Mobility at the VT Transportation Institute (VTTI), along with colleagues Hao Chen, research associate at VTTI; Mansoureh Jeihani, Ph.D., associate professor in transportation and urban infrastructure studies at MSU; and Celeste Chavis, Ph.D., assistant professor in transportation and urban infrastructure studies at MSU, are leveraging this communication, developing ESC algorithms for buses using predictive energy estimation models. These models identify optimum speed profiles using information from surrounding vehicles and upcoming signalized intersections.

The goal is to predict the most efficient speed to move a bus through an intersection and reduce ‘stop/go’ behavior, a key reason for inefficient fuel economy. The ability to move buses through intersections efficiently could result in significant fuel savings and reduced emissions.

The first phase of the study is underway, with field testing to begin this summer at the Smart Road Test Facility at VT. This full-scale, closed test bed is managed by VTTI and owned/maintained by VDOT. It features 2.2 miles of paved lanes with 14 pavement sections. Embedded sensors detect moisture, temperature, strain vibration and weigh-in motion. The facility can even create artificial snow of up to 4” per hour as well as fog. To test the ESC system tailored for buses, three test conditions will be compared and evaluated:

  1. Uninformed driver: no data will be communicated (no speed adjustment)
  2. Countdown: the bus driver will be provided with a “time to red light” countdown every 2 seconds (self-adjusted speed)
  3. Recommended speed profile: the driver will be given an audio alert every 2 seconds with a recommended speed (prescribed speed).

It is anticipated that buses traveling at the calculated, prescribed speed will realize the highest energy efficiencies. Adjusting speed by even a few miles/per hour, while reducing braking and accelerating, can have significant impact on fuel savings over time.

Vehicle Onboard Unit Hardware (Top) and Driver Interface (Bottom) in the VTTI Eco-Speed Control System

The researchers are pleased to be leveraging the resources offered by the Smart Road facility. “The test facility allows us to test our algorithms that compute optimum vehicle trajectories using real drivers in conditions as close to reality as possible without actually being on the roadways,” explained Rakha. “We can test a variety of conditions and delays without jeopardizing the safety of any surrounding vehicles.”

The MSU team will implement and test the ESC algorithms developed by VT in a driving simulator to extend the previous controlled field tests on light-duty vehicles to test under more complex conditions, such as considering different approach speeds and multiple signalized intersections.

When the project wraps up in mid-2018, the team hopes to better understand the challenges associated with dynamic traffic conditions and real-time data computation as well as the differences in responses based on vehicle powertrain type and electric battery state-of-charge. Ultimately, they hope all buses will be able to drive more efficiently near intersections, reducing travel time and fuel consumption.

For more information, contact Dr. Rakha at hrakha@vt.edu.