Abstract
North American heavy haul railroads are experiencing growth in traffic demand and increasingly facing capacity constraints. A key factor influencing railroad operations is heterogeneity in train characteristics. Different train types can have substantially different operating characteristics including maximum speed, power-to-ton ratio and dispatching priority. This heterogeneity causes conflicts between trains that increase delays and reduce capacity. Dispatching simulation software was used to analyze the effect of various combinations of intermodal and bulk trains on a hypothetical, signalized, single-track line with characteristics typical of a North American freight railroad subdivision. This assessment studied the relationship between volume, heterogeneity and delay. Further work identified the key factors that contribute to the increased delays due to heterogeneity. The train characteristics of speed, acceleration, braking and priority were considered for their effect on the increased delays due to heterogeneity. Understanding these factors that affect delay allows for more effective network capacity planning and efficient rail operations. The results also suggest certain railway operating strategies that may reduce the delays caused by train-type heterogeneity thereby improving service reliability