Minnesota Department of Transportation
Many northern states allow an increase in the gross vehicle weight (GVW) for certain vehicles during the winter to more efficiently use the increased load carrying capacity of frozen pavement structures. The increased load limits and dates are usually set according to legislation, which may not account for seasonal differences in the depth of frost. This report documents the effects of increasing the winter load limits for a pilot study in Minnesota and suggests a possible method for placing and removing increased winter load limits. A pilot study was conducted in which the northern sugar beet haulers were allowed to increase the winter weight of the 6-axle tractor-trailer combination vehicles from 391 kN (88,000 lbs.) to 416 kN (93,500 lbs.). This load limit was chosen to match North Dakota since this was the final destination. The sugar beet haulers were allowed to increase the GVW when the frost level reached 150 mm (6 in.) into the subgrade layer and end when 150 mm of the base layer thawed. Frost and thaw depths in the pavement structures were monitored with Watermark and thermocouple sensors. It was found that there was a significant increase in the structural carrying capacity of the frozen pavement as measured by decreased deflections during falling weight deflectometer testing. A similar trend was seen in the strain data from the Mn/ROAD site. The condition surveys conducted showed no visible signs of increased surface distress due to the increased loads, however the results from this study are limited because the transporter was only able to participate in the study for three weeks. Several recommendations related to improving seasonal load limit implementation are suggested and subsequent activities during the 2000-2003 period are described.
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