Modified Supplementary Safety Measure (SSM)

An SSM that has in some way been adjusted to accommodate unique circumstances existing at a specific highway-rail grade crossing and no longer conforms to the SSM requirements. Modified SSMs are considered ASMs. An example would be traffic channelization devices that due to a nearby intersection are only 45 feet in length instead of the required 60 feet.

Source: Federal Railroad Administration

Last reviewed October 2023