Risk and Train Control: A Framework for Analysis

The effects of train control strategies on the risks of railroad operations are examined. Analysis of a hypothetical 1800-km (1, 200-mi) corridor identified the main factors that increase risks. Passenger traffic is the most important factor because the addition of passenger trains creates the possibility of catastrophic accidents with dozens of fatalities. Increasing the number of trains per day leads to more than proportional increases in the risks of collisions. Single-track operations are much more susceptible to collisions, whereas higher train speeds increase both the likelihood and the severity of the consequences of accidents if there is a signal overrun or a failure to obey a slow order. Positive train control (PTC) systems can reduce most, but not all, of the collisions and overspeed derailments, as improper train handling or equipment failure could still lead to accidents. Establishment of a digital communications link to the train should also allow the possibility for improved grade-crossing protection. For the hypothetical corridor, the potential benefits from improved grade-crossing protection were on the same order of magnitude as the predicted benefits from PTC systems. If new technologies are developed to detect broken rails, the digital communications link could also be used to implement immediate braking, thereby preventing some additional derailments. The risk-based approach demonstrated may provide a more complete assessment of rail risks than a methodology that estimates safety benefits based on documentation of accidents that might have been prevented if more advanced train control techniques had been in place. Risks include the possibility of catastrophic accidents, whether or not such accidents occurred recently. A causality-based methodology also allows greater flexibility in sensitivity analysis and in assessment of trends in traffic volume, traffic mix, and other factors.