Measuring the Impact of Additional Rail Traffic Using Highway & Railroad Metrics

Long term demand for freight movements in North America is expected to increase dramatically in the coming decades. The railroads are poised to take on this additional traffic assuming the capacity is available. Measuring the capacity of these rail lines is complicated by the interrelationships between asset utilization, reliability, and throughput. There is not a single metric that captures these intricacies. Capacity can be determined by delay-volume relationships, utility models, or economic study. For many case studies, railroads use parametric and simulation modeling to determine the train delay per 100 train miles. This metric does not tell the full story; especially when comparing different train types. The highway industry uses a different portfolio of metrics that can be adopted by railroad capacity planners. These metrics can be more sensitive to the worse performing trains. Additionally, these metrics can control for increased delay simply due to additional traffic. These concepts are illustrated by simulating the impact of additional 110 mph passenger service to a single track freight line. INTRODUCTION The North American railroad network is expected to experience continued growth in freight traffic. Overall freight demand is projected to increase 84% by 2035 [1]. New passenger services are being proposed to operate over portions of the freight railroad infrastructure. The freight railroads continue to invest in intermodal freight cars and terminals [2]. These faster train types have different characteristics in terms of acceleration, braking, top speed, priority and on-time performance. The impact of the new traffic can vary drastically based on the metrics used. Additionally, the term “capacity” can have different meanings to different stake holders. There are many metrics used both by the railroad and highway industry to analyze and plan operations. A subset of these will be examined in this paper. Additionally, railroads and highways have certain key traffic relationships that will be compared. These metrics and traffic relationships are then illustrated by simulating shared corridor operations with freight and passenger trains. TRANSPORTATION METRICS There are four important definitions of railroad capacity as defined in a study conducted by Transport Canada in 1979 [3]: 1. Practical Capacity: Ability to move traffic at an “acceptable” level of service 2. Economic Capacity: The level of traffic at which the costs of additional traffic outweighs the benefits 3. Engineering Capacity: The maximum amount that can possibly be moved over a network 4. Jam Capacity: The system has ceased to function and all trains are stopped The first and second definitions of capacity are the most relevant. Rail lines should continue to serve new traffic until the problems of congestion are greater than the benefit of additional traffic. Practical Capacity implies that there is a standard quality of the service that the railroad will maintain. Economic Capacity is determined by calculating the traffic level where the actual costs of congestion equals the revenues of additional traffic. The engineering capacity is the maximum flow through the network and often corresponds with high variability. There are three broad categories to measure the level of service or capacity of a railroad as shown in Figure 1. The first is the throughput, the amount of goods and people that the transportation network serves per unit of time. The second is reliability of the service provided by the transportation network. Higher reliability often requires more physical resources. Lastly there is the overall utilization of the existing assets. Poor asset utilization can consume the available capacity of the railroad network. A capacity expansion project can be undertaken to increase throughput as well as increase reliability. Often, capacity projects can be postponed if more efficiency can be Proceedings of the 2012 Joint Rail Conference JRC2012 April 17-19, 2012, Philadelphia, Pennsylvania, USA