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South Dakota Department of Transportation
Project Synopsis

Title: Effects of Off-Road Equipment Tires on Flexible and Granular Pavements
Project Researcher: Sebaaly & Epps, University of Nevada
Project Manager: Dave Huft
Research Period: 12/1/1999 - 11/30/2001
Cost: $200,000.00

Problem Statement: In recent years, manufacturers have designed innovative equipment for off-road agricultural and construction use. Equipment such as fertilizer applicators, grain carts, and heavy construction machinery has become larger and heavier, and is often supported by unconventional tire configurations, including low-pressure floatation tires, lugged tires, or rubber tracks. The equipment has been optimized for off-road traction and effectiveness, not necessarily for over-the-road transportation.

South Dakota's emphasis on vehicle weight enforcement has focused attention on the fact that such equipment often exceeds legal load limits if loaded with commodities, and sometimes even when unloaded. For convenience and economy, equipment users prefer driving such equipment over state and local roads (typically surfaced with gravel or asphalt pavement) to off-road work locations. Because of regular and seasonal load limits, they must often transport equipment and commodities separately at extra labor and expense. Equipment users have questioned whether the load limits are appropriate, in light of the fact that many of the off-road vehicles are designed to minimize soil compaction in off-road use. In lay terms, the question is "If this equipment is designed to reduce soil compaction, and can run over small plants without damaging them, how can it possibly damage roads as much as ordinary truck tires with the same weight per axle?"

Unfortunately, the effects of such loads and tire configurations on pavements are not well known. Most models of pavement damage are derived from road tests using conventional truck tires, and cannot predict pavement response under other tire configurations, pressures, or footprints. Without knowledge of the effects of off-road equipment on typical state and local pavements, it is impossible to assess the financial impacts of its use, and to determine whether present regulations are too strict, too loose, or appropriate.

Research is needed to evaluate the physical effects of such loads on pavements, to assess economic impacts, and to provide a basis for possible regulatory changes.

Findings: Field tests showed that application of heavy loads supported by off-road tires caused significantly higher levels of vertical deflection and pressure in the base and subgrade of flexible and granular pavements. On flexible pavements, significantly higher levels of strain at the bottom of the hot mix asphalt layer were also observed. Using a computer model validated by the field testing, the research showed that such loads would be expected to cause very significant increases in pavement damage on a wide range of flexible and granular surfaces that exist on South Dakota's state and local highway networks. On the basis of field testing, model verification, and modeling of structural and climatic conditions that exist in South Dakota, researchers concluded that no relaxation of current vehicle weight restrictions was warranted.

Research Objectives:
1  To model pavement damage caused by tires and tracks on off-road equipment.
2  To assess the economic benefits and costs associated with the use of off-road tires and tracks under present regulations.
3  To recommend policies for regulating transportation of off-road equipment over state and local highways.

Research Tasks:
1  Meet with the project's technical panel to review the project's scope and work plan.
2  Thoroughly review literature pertaining to the effects of off-road equipment tires on flexible and granular pavements.
3  Identify primary factors relating to equipment, granular and flexible pavements, and environment, that affect pavement response to load.
4  Propose and test a theoretical model of pavement response under load applied by off-road equipment tires and tracks.
5  Meet with the technical panel to review the pavement response model and to confirm plans for its field validation.
6  Measure the in-situ response of representative granular and flexible pavements under load applied by off-road equipment tires and tracks. Measurements should span seasons during a full year, on three pavement types (gravel, thin asphalt, and thick as
7  Validate and refine the pavement response model based on results of the in-situ measurements.
8  Using results obtained from the validated pavement response model, estimate the amount of pavement life consumed by application of loads by representative off-road equipment tires and tracks.
9  Meet with the technical panel to review the results of Tasks 6-8 and to refine plans for remaining tasks.
10  Estimate pavement damage costs attributable to loads applied by off-road equipment tires and tracks, as well as the economic benefits to users of the equipment, and compare them.
11  Develop recommendations for regulating transportation of off-road equipment over state and local highways, in consideration of the balance between associated costs and benefits.
12  Prepare a final report summarizing research methodology, findings, conclusions and recommendations.
13  Make executive presentations to SDDOT's Research Review Board and a meeting of industry associations at the conclusion of the project.

Documents Available:

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