The purpose of this research was to evaluate the long-term settlements for a wide variety of at-grade crossings. Twenty-four highway crossings were monitored to determine the effects of enhanced support on minimizing long-term settlements of the crossing surfaces. Settlements of the rail and highway approaches to the crossing areas were compared to settlements of the common crossing areas over an average service period of three years. Long-term settlements of crossings with traditional all-granular support materials were compared to crossings with enhanced support. The enhanced support was provided by substituting a layer of asphalt (termed underlayment) for the all-granular subballast layer.

The trackbed crossings underlain with asphalt settled 41% of the amount for the all-granular supported trackbed crossings. In addition, the crossing areas underlain with asphalt settled 44% of the abutting allgranular supported track approaches. The statistical t-test validated the significance of the differential findings. Settlements of the all-granular track approaches to the crossings were statistically similar to each other and to the settlements of the all-granular crossing areas.

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