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Every spring, thousands of kilometers of local roads have load restrictions due to pavement structural weakness. Load restrictions vary greatly across North America, but often are severe enough that all large trucks are banned outright or greatly limited in haul capability. An assessment of the potential of central tire inflation (CTI) systems to mitigate or reduce the impact of seasonal load restrictions was made. Overall, CTI equipped trucks and lower tire pressures can be of benefit in allowing truck trips on aggregate surfaced roads and roads with relatively thin bituminous surfaces (less than 75 mm) that otherwise would be precluded.

This paper discusses the results of testing variable tire pressure in two of Weyerhaeuser's logging operations in Western Washington. Ten log trucks had prototype Eaton central tire inflation systems installed, five at Raymond and five at Vail. The trucks were involved in cooperative testing with the U.S. Forest Service and the Universities of Washington and Idaho. A test at Raymond, Washington compared high and low tire pressure on roads constructed from weak sandstone rock typical of the Southwest Washington coastal area. The test showed a significant improvement in traction and a reduction in road maintenance with low tire pressure compared to the high tire pressure. A test at Vail, Washington evaluated the effect of low tire pressure on varying surface thickness. Low tire pressure trucks were able negotiate 18 percent adverse grades unassisted, with loads exceeding 43,000 kg.