Impacts of Road-Trains on the Geometric Design of Highways

Abstract

For enhanced efficiency and sustainability, transportation must rely on new technologies. Researchers and engineers work nowadays on many valuable and green transportation ideas. One such idea creates vehicle platoons on freeways to achieve multiple benefits: reductions in gas consumption, vehicle emissions, and traffic congestion through enhanced aerodynamics and road space utilization, as well as improvements in safety and driver comfort through fail-safe mechanisms and moderation of collision damages given similar vehicle speed. The technological enhancements are built into the vehicles. The existing freeway infrastructures do not necessitate modification. Still, the interactions between the human factors, or lack thereof, and the new technologies may directly impact the traditional guidelines for freeway design. Over time, the dedicated freeways of the future, whether rehabilitated or built anew, could satisfy guidelines derived specifically for road-trains. Further, freeways built to current guidelines may accommodate travel speeds higher than those originally anticipated per design. It remains to understand (1) why existing freeway lanes can accommodate road-trains, (2) whether design guidelines for road-trains are significantly different from current guidelines, and (3) whether road-train operation results in significant a posteriori design speed increases. This article seeks to answer these very questions. The investigation of a continuum of transitory to end state scenarios concluded that road-trains promote both shorter required and longer available sight distances, thereby promoting the adequacy of existing freeways. It is shown that road-trains reduce minimum length requirements and increase a posteriori design speeds for all curves. Changes are less drastic for horizontal than vertical curves.