1 Introduction
2 What is capacity?
2.1 Capacity concept and definitions
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Absolute train-path harmony (the same parameters for majority of trains)
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Minimum headway (shortest possible spacing between all trains)
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Providing best quality of service [7].
2.2 Capacity metrics
3 Differences between the U.S. and European rail systems
3.1 Infrastructure characteristics
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Public versus private ownership of infrastructure The ownership of rail infrastructure is one of the important differences between Europe and the U.S. rail networks. More than 90 % of the infrastructure is owned and managed by private freight railroads in the U.S., while in Europe almost all infrastructure is owned and managed by governments or public agencies. In addition, operations and infrastructure are vertically separated in Europe, while in the U.S. the majority of operations (mainly freight) are controlled by the same corporations who own the infrastructure. The ownership and vertical separation have wide impact in the railroad system. Perhaps the greatest effect is on the prioritization of operations and accessibility for operating companies, but other aspects, such as operations philosophy, maintenance strategy and practices, signaling and train control systems, rolling stock configuration, and capital investment strategies are also affected [4, 11].
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Directional versus bidirectional Most of the U.S. double tracks operate in bidirectional fashion and use crossovers along the corridor, while directional operation with intermediate sidings and stations is the common approach in Europe [4].
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Distance between sidings The distances between stations and sidings in the European rail network are generally shorter than in the U.S. The average distance between sidings/stations throughout the European network (total route mileage vs. number of freight and passenger stations) is approximately four miles between sidings/stations in both UK and Germany [13, 14]. In the U.S., the distance between sidings varies greatly between corridors. On double track sections, passing sidings are typically further apart than in Europe, often more than twice the average European distance [11, 15].
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Grade crossings There are approximately 227,000 active grade crossings along the main tracks in the U.S. [17, 18], while there are few grade crossings on the main corridors in Europe, partially due to higher train speeds. High frequency of grade crossings and difficulty of their elimination cause operational and safety challenges for increased train speeds in the U.S. [19].
3.2 Signaling characteristics
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Manual blocking versus signaling systems Manual blocking is absent on main passenger corridors in the U.S. today, but relatively common on lower density branch ones, including some of the lines proposed for passenger corridors. In Europe, most shared-use corridors are equipped with one of the common signaling systems [20].
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Cab signaling A more significant difference is the extensive use of cab signaling and enforced signal systems, such as ETMS and ATS in Europe. Implementation of automatic systems is limited in the U.S., despite the current effort to introduce the positive train control (PTC) on a large portion of corridors [11].
3.3 Operation characteristics
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Improvised versus structured operation While some specific freight trains (mainly intermodal) have tight schedules, the U.S. operations philosophy is based on the improvised pattern with no long-term timetable or dispatching plan. On the passenger side, the daily operation patterns of many Amtrak and commuter trains are also developed without details, anticipating improvised resolution of conflicts among the passenger trains, or between passenger and freight trains. In Europe, almost all freight and passenger trains have a regular schedule developed well in advance, known as structured operations [21].
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Delay versus waiting time Delay (deviation of train arrival/departure time from what was predicted/planned) and waiting time (scheduled time spent at stations for passing or meeting another train) are two fundamental concepts in the railroad operations. The waiting time concept is typically used in Europe to manage rail operations, due to the structured operations pattern with strict timetables. Delay is more commonly used in the U.S. capacity analysis as the main performance metric, while it is limited in Europe to the events that are not predictable in advance [21].
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Punctuality The punctuality criteria of trains are quite different in the U.S. and Europe. Amtrak’s trains are considered on-time if they arrive within 15 min of a scheduled timetable for short-distance journeys (less than 500 miles) or within 30 min for long-distance trains (over 500 miles). In 2011, Amtrak’s train punctuality was 77 % for long-distance trains, 84 % for short-distance trains, and 92 % for Acela trains on Northeast Corridor. According to Amtrak, more than 70 % of passenger train delays were caused either by the freight trains performance or infrastructure failure [23]. The passenger trains in Europe have shorter average delay per train. For instance, Network Rail in the UK reported that approximately 90 % of all short-distance passenger trains had less than 5 min deviation from planned timetable, while for long-distance trains, the same was true for deviation less than 10 min [24]. In Switzerland, more than 95 % of all passenger trains are punctual with an arrival delay of 5 min or less [25]. The punctuality of European freight trains in 2003 was reported to be approximately 70 % [26].
3.4 Rolling stock characteristics
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Train configuration (length and speed) Typically freight trains in the U.S. are longer and heavier than freight trains in Europe. Based on the Association of American Railroads (AAR), the typical number of cars in a U.S. freight train varies between 63–164 cars in the West and 57–110 cars in the East, while the typical number in Europe is 25–40. From speed perspective, the average speed of intercity passenger trains in Europe is significantly faster than in the U.S. [2, 11, 16]. Freight trains also typically operate at higher speeds and with less variability in Europe.
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Diversity of freight versus passenger trains The U.S. rail transportation is more concentrated on the freight trains than Europe, and there is a great diversity between the types, lengths, etc., of freight trains. On the passenger side, Europe has more diverse configurations (such as speed, propulsion, train type, power assignment, HSR services, diesel, and electric multiple unit (EMU) trains) in comparison to the U.S. [2, 20].
4 Capacity measurement, analytical, simulation, and combined approaches
4.1 Analytical approach
4.2 Simulation approach
4.2.1 Simulation methods: timetable based versus non-timetable based
4.3 Combined analytical–simulation approach
5 Review of capacity studies in the U.S. and Europe
5.1 Studies with analytical approach
5.2 Studies with simulation and combined approach
5.3 Detailed assessment of selected studies
Category/subcategory | The U.S. (14 studies) | Europe (11 studies) | |
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Capacity approach | Analytical | – | |
Simulation | |||
Combined analytical–simulation | |||
Tools/software | Only mathematical/parametric modeling | – | |
General simulation software | – | ||
Timetable-based simulation software | – | ||
Non-timetable-based simulation software | – | ||
Purpose of research | New methodology development/methodology approval | ||
Master plan/capacity analysis | – | ||
Academic research/project | |||
Type of outcomes/solutions | Delay analysis/improvement | 1 study [69] | |
Infrastructure development, | 1 study [2] | – | |
Rescheduling/operation changes | |||
Combination of above solutions | |||
New tools/methodology approval | |||
Validation of simulation results | No comparison | ||
Base model | |||
Base and alternative results | 1 study [32] | 1 study [68] |
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No comparison No specific information or comparison was provided between simulated results and actual practices. As presented in Table 1, approximately one-third of the studies (9 out of 25) did not validate the simulation results, either because the study was not based on actual operational data, or comparison was not conducted as part of the research.
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Base model Only the results of a base model were compared with the real data. More than half of the studies (14 out of 25) compared the simulation results only with the base model.
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Base and alternative results In addition to base model comparison, the alternative outcomes were compared with the real data. Only two studies belonged to this category.