Low Speed Acceleration of Tractor-Semitrailers Equipped with Automated Transmissions

The distance, velocity and acceleration characteristics versus time of heavy trucks for use in accident reconstruction have been the subject of studies by Grimes and others. To date, the majority of the research has been done using tractor-semitrailers equipped with standard transmissions. In recent years, as transmission technology has improved, automated and automatic transmissions are becoming popular on North American roadways. A series of tests were performed to document the acceleration characteristics of two different tractors, a 2007 Volvo VNL and a 2011 Freightliner Cascadia, both equipped with automated transmissions towing both empty and loaded semitrailers. The vehicles were instrumented with a Racelogic™ VBOX III GPS data-logging device that measured speed. Other vehicle parameters were logged using the recording software manufactured for the specific engine manufacturer. This paper presents the data from these tests and discusses the acceleration characteristics of heavy trucks equipped with automated transmissions. Unlike fully automatic transmissions, automated transmissions have a clutch. Most have a clutch pedal but the clutch pedal is only utilized when the vehicle is first put in motion.