Impact of Passenger Trains in Double Track Networks

North American freight railroads are expected to experience increasing capacity constraints across their networks. To help plan for this increased traffic, railroads use simulation software to analyze the benefits of capacity expansion projects. Simultaneous operation of heterogeneous traffic further increases delay relative to additional homogenous traffic. Additional passenger trains can cause more delays to freight trains than additional freight trains. Rail Traffic Controller (RTC) was used to run simulations with varying mixes of unit freight and passenger trains operating at various speeds on a double track configuration. Basic assumptions on the relative difference in priority between train types lead to drastically different results on the impact of adding higher priority trains. This assumption dictates whether the track in the opposing direction should be used for overtake maneuvers. Also, higher speed differentials between train types can result in higher delays as faster trains catch up to slower trains more quickly. These analyses will help planners improve their understanding of the tradeoff in capacity due to operation of different types of trains at different priorities and speeds. INTRODUCTION Long-term freight demand is projected to increase 84% by 2035 [1], and new passenger services are being proposed to operate over portions of the freight infrastructure. These train types have different characteristics in terms of acceleration, braking, top speed, priority and on-time performance. Their unique characteristics place different demands on the freight infrastructure. Operating multiple train types on one line can introduce higher delays than operating a single train type [2]. Higher speed passenger trains in shared corridors introduce new challenges in managing the existing capacity of the railroad. Simulation analysis has been used to analyze the delay caused by the interactions of unit trains and intermodal trains. Simulation techniques have also been used to study the interactions between passenger train speeds and bulk freight trains on single track [3]. The objective of this paper is to analyze the impact of adding passenger trains to double track freight railroad networks. We used simulation software called Rail Traffic Controller (RTC) to evaluate effects of homogeneous and heterogeneous operations [4]. Delay, measured in minutes per 100 train miles, is the main output from the simulation analyses. Delay is defined as the difference between the simulated actual run time and the simulated minimum run time (MRT). The MRT is the fastest a particular train can traverse the network with no interfering traffic, slow-orders or other external factors that could cause the train to deviate from normal track speed. The delay includes time for meets and passes, and excludes time spent at scheduled stops. This metric provides insight into the capacity of a line. All delay values presented in this analysis refer to the performance of the trains on a line and not the maximum number of trains that can be operated on the line. Background Double track lines can move more traffic than single track by removing the need for trains to start and stop at sidings to allow the other train to clear the bottleneck section. The largest component of delays for train interaction in single track is the meet delays at these sidings [5]. Subsequently, double track lines should have very small meet delays. Because of these inherent efficiencies, double track lines can be utilized to run more trains at higher average speeds than single track configuration. When speed differentials are present in double track configurations, there are two options to resolve the conflict when a fast train catches up to the slower train. The first option is to delay the fast train and slow it down to the speed of the slower train. Another option is to preserve the on time performance of the faster train by using the 2 nd track for an overtake maneuver. There are two methods of accomplishing this maneuver. The first is to have the slow train use a crossover to transfer to the 2 nd track and allow the fast train to pass at its track speed. The slow train will then take the next available crossover to return to the original track. Another approach is to have the faster train change its speed to that of the crossover speed and transfer to the 2 nd track. The faster train Proceedings of the 2012 Joint Rail Conference JRC2012 April 17-19, 2012, Philadelphia, Pennsylvania, USA