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The objective of this study was to evaluate the concept of a heavy-duty tractor - motorized semi-trailer hybrid electric combination, which would have electric drive axles on the semi-trailer. The scope of the project included an analysis of the general concept of a power-driven semi-trailer, the positioning of the concept of the heavy-duty tractor - motorized semi-trailer hybrid electric combination in the general context of the technology, and the evaluation of the applicability of the concept for different duty cycles. Several transport activities were analyzed to determine specific duty cycles for heavy-duty vehicles: highway line haul and regional haul, construction haul, and off-highway hauling of raw materials, such as forestry transport with Class 8 and off-highway tractor-trailer combinations.

This study aimed to evaluate several rolling resistance reduction measures applicable to class 8 tractor-trailer combinations. Two methods have been employed: fuel consumption tests according to the SAE J1321 Joint TMC/SAE Fuel Consumption Test Procedure - Type II, and long-term operational observations using control and test vehicles monitored throughout baseline and test periods. One way to reduce the rolling resistance is to use wide-base tires: two different Type II fuel consumption tests revealed a more than 9 % improvement in fuel economy for a tractor-trailer combination equipped with wide-base tires. Long-term operational observation assessed the use of single wide-base tires on two 8-axle B-train tractor-trailer combinations. The results showed an average 5.11% fuel improvement and an average 4.37% energy intensity improvement. Other tests compared single-wide base tires with different tread patterns and tire compounds.

The objective of the project was to compare the fuel consumption of a prototype hybrid electric CNG truck with that of two trucks: a CNG truck and a diesel truck for the similar market and operating conditions. The tests were conducted on a test route representative of the conditions encountered by these vehicles in normal driving operations. The test route length was 276 km with a maximum altitude difference of 374 m. The test route had four sections, including a hilly section with a length of 88 km. The result of the comparison between the two CNG trucks was expressed as fuel savings of CNG in percentage. The fuel consumption of the diesel truck was accurately measured using the gravimetric method. The hybrid electric CNG truck showed average fuel savings of 3.6% and demonstrated up to 7.7% in savings for the entire trip compared to the CNG truck.