1986-11-01

The Need For a 4×4 Tractor - Friction or Fiction? 861983

The need for a commercially available 4 × 4 tractor has been anticipated for over 20 years. With completion of the main part of the interstate highway system in the 1970's, many thought legislation allowing use of triples and other longer combination vehicles would be adopted quickly to obtain the inherent efficiencies. Such legislation did not pass until 1982. Consequently, only limited operation of longer combinations was allowed on toll roads and on some western highways prior to 1982.Over the years various tractor and component manufacturers have developed 4 × 4 components and 4 × 4's for the expected needs stimulated by proposed weight-horsepower regulations, predicted longer combinations and increased traction requirements, and the need for greater vehicle stability. Most of these needs never materialized, but speculation prompted spurts of 4 × 4 development.The primary need for 4 × 4's has been mountain pass operations. The demand for this type of vehicle has always been very small, therefore manufacturers have responded with specially built vehicles in limited production.With advent of the Surface Transportation Assistance Act (S.T.A.A.) in 1982, authorizing triples, long doubles, and other combinations with chassis dimension flexibility, the need for a 4 × 4 tractor needs reassessment.This paper reviews the various componentry and configurations of 4 × 4 tractors that have been available in the past, and discusses their merits and shortcomings from a fleet operator's point of view.A new 4 × 4 approach will be discussed that takes advantage of the flexibilities permitted by the S.T.A.A. legislation. User demand for 4 × 4's should increase as more states approve longer combinations. The economic and safety benefits of operating longer combinations in inclement weather, the ability to use higher horsepower engines to meet trip requirements, and the increased possibility of obtaining state approval for longer combinations dictate reconsideration of the need for a commercially available 4 × 4.

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