Adjacent-track accidents (ATAs) have been identified as an important hazard on shared-use rail corridors. In these train accidents derailed railroad equipment intrudes on (fouls) an adjacent track, disrupts operations, and potentially causes a collision with trains operating on the fouled tracks. Derailments without intrusion may cause equipment and infrastructure damage, passenger casualties, and disturbances to system operation; however, an intrusion may be even more severe because of the potential involvement of multiple trains. Opportunities for ATAs have increased in recent years because of expanded passenger and transit service on freight railroad trackage, right-of-way, and corridors and because of increased multiple tracks related to capacity expansion projects. This paper presents a probabilistic risk assessment methodology for analyzing ATA risk. An event tree is created to identify scenarios for ATAs, and a fault tree analysis is performed to identify basic events that contribute to such accidents. The quantitative probability of an ATA is derived by using Boolean algebra on the basis of the results of the fault tree analysis.