Implementation of Spring Load Restrictions on the State Highway System
North Dakota Department of Transportation procedure for initiation of spring load restrictions on the State Highway System is based on the following factors:
- The department utilizes load restrictions to reduce damage to roadways caused by heavy weights at a time of the year when highway pavements are most vulnerable. The department sets load restrictions as weather and roadbed conditions require, and lifts these restrictions when roadbeds are stable enough to carry traffic without damage.
- The initiation of load restrictions can come as early as late February to mid March. Load restrictions normally are initiated in the southwest portion of the state, and are phased out in the northeastern portion of the state by late May.
- The department primarily uses three factors in the posting of load restrictions.
These factors or indicators are:
- Temperature probes in the base layers of pavement sections. As these temperatures approach 32Edegrees, the department starts planning the posting of highways with pavement sections which do not have sufficient strength to sustain the transport of heavy loads during periods of soft base structures.
- Long range temperature forecast. When long range temperature forecasts indicate that low temperatures are approaching the freezing point, with daily highs in the upper 30's or 40's, load restrictions are planned.
- Falling weight deflectometer (FWD). This equipment measures the strength of the bases, as well as the asphaltic pavement surfaces. The department utilizes the FWD to evaluate pavement strengths for purposes of forecasting when load restrictions may be lifted. The data base generated by the FWD, in combination with long range weather forecasts and area wide moisture conditions, provides the basis for lifting load restrictions.
It has been the department's experience that the most significant pavement damage occurs during the first four weeks after the onset of the spring thaw. This aspect has focused the department towards close monitoring of both weather forecasts, along with sub-base temperatures, and posting of load restrictions on short notification with the overall objective of limiting damage to the highway system.