Supplementary Safety Measure (SSM)

SSMs are engineering improvements, which when installed at highway-rail grade crossings within a quiet zone, would reduce the risk of a collision at the crossing. SSMs are installed to reduce the risk level either to the level that would have existed if the train horn were sounded (compensating for the lack of the train horn) or to a level below the Nationwide Significant Risk Threshold. Approved SSMs include:

  • Four quadrant gates
  • Gates with medians or channelization devices, also known as traffic separators
  • One-way streets equipped with gates that fully block the street
  • Temporary closure (i.e., nighttime closure)
  • Permanent closure

Source: Federal Railroad Administration