Diesel trucks play a crucial role in transportation activity and a major contributor to fuel consumption and air pollution. To improve the energy efficiency of diesel trucks, we develop a truck eco-approach and departure (EAD) system based on Signal Phase and Timing (SPaT) message from signal controllers and road grade information along the path. The proposed model consists of two levels—the lower level for powertrain-based fuel consumption estimation and the upper level for optimal trajectory planning. The powertrain model is designed for a diesel engine with a six-gear transmission and well calibrated using on-board Electronic Control Unit (ECU) data. The trajectory planning model is formulated as a shortest path problem with the combination of time, distance, and speed as the state on each node and fuel consumption rate as the cost on state transition. Numerical experiments are conducted at a hypothetical pre-timed signalized intersection with varying entry times and speeds. The average energy savings compared with an uninformed driver is 11.0% for level terrain, 5.8% for uphill terrain, and 20.2% for the downhill case. The energy savings compared with the baseline trigonometric EAD algorithm is 5.4% for level terrain, 3.7% for uphill terrain, and 6.5% for the downhill case. This research also found that even without knowing the road grade and weight information, the proposed EAD algorithm, assuming zero grade and average weight, still achieves significant fuel savings, although that information can bring up to 1.5% of additional savings.
