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68 Shared Use of Railroad Infrastructure with Noncompliant Public Transit Rail Vehicles: A Practitioner's Guide for Options 2, 3, and 4, will deliver a safety performance equivalent to or better than for Option 1, with full temporal separation. Option 1 is comparable to several existing shared-track operations in the United States, notably those on the San Diego Trolley and the River LINE in southern New Jersey, and is used in this analysis as a base case that defines the standard of acceptability for safety performance. The risk analysis methodology shown is an adaptation of that used and fully described in a recently completed (but not yet published) report to the FRA, "ITS Technologies for Integrated Rail Corridors." The analysis is intended to convince a transit authority considering a concur- rent shared-track operation with light rail passenger cars and low density conventional freight that a safety performance acceptable to FRA can be achieved, and that such projects are worth further development. A much more exacting analysis would be required for submittal to regula- tory authorities in support of a waiver application and would have to include a more detailed ana- lytical back-up for model input parameters and a precise breakdown of accident scenarios. Risk analysis has been applied to the four shared track options as described in detail in the Task 10 report. All four options combine a basic passenger service with 15 minute intervals dur- ing peak hours and 30 minute intervals in off-peak hours with two freight round trips a day and en route switching at two locations along the shared track. The key differences among the options that affect safety performance are given in Table 18: The following sections describe elements of the risk modeling methodology, the inputs to the model and the results obtained. Risk Analysis and Modeling Methodology The risk analysis methodology used in this analysis is a comparative quantitative risk analysis: the conclusions from the analysis are based on a comparison between the analysis cases rather than the absolute results. Many inputs are common to all the analysis cases, and even where the inputs vary between analysis cases, common sources and approaches have been used to estimate input values. This means there can be higher confidence in the relative comparisons than in the absolute quantitative results. The basic steps and building blocks of all risk analyses are explained here and shown in Figure 6. Identify hazards. The first item in any risk analysis is to identify the hazards that will be the subject of analysis. In this case, the analysis is concerned with train accidents that can cause harm to passenger train occupants. While train operations on the shared corridor can result in harm Table 18. Key safety features of the four options. Option Description Freight Signal System Other Safety-Related Operation Features 1 Full Temporal Night Conventional Split Point Derails at Separation Operations CTC Freight-Only Connections Only 2 Concurrent Unrestricted Automatic Train Two Freight Diamonds Separate Daytime on Stop at Stop Crossing Passenger Tracks Parallel Single Separate Tracks Signals with Split Point Derails Track and Full ATS Protection 3 Concurrent In Passenger Cab Signals Split Point Derails at Shared Single Off-Peak Hours with Speed Freight-Only Connections Track Enforcement 4 Concurrent In Passenger Cab Signals Split Point Derails at Shared Double Off-Peak Hours with Speed Freight-Only Connections Track Enforcement
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Shared-Track: A Handbook of Examples and Applications 69 Estimate Likelihood Yes Is It Identify Estimate Adequately Acceptable Hazards Risks Safe? No Estimate Consequences Modify System Figure 6. Basic risk analysis process. to other parties, for example highway users at grade crossings or trespassers, the risks to these parties is minimally affected by the different forms of track sharing and have not been included in the analysis. There are two categories of specific hazards or accident scenarios described in this analysis: I. Shared Track Operations--variable by option, time of day and analytical focus: 1. Train-to-train collisions, whether between two passenger trains or between a passenger and freight train. 2. Intrusion collisions, where freight equipment intrudes on the active passenger track, either because of a freight derailment on an adjacent track, a shifted load or a roll-out event at a connecting switch. 3. Collisions at diamond crossings where freight movements cross active passenger tracks. Movements across a diamond are a feature of Option 2. II. All Railroad Operations--common to all rail operations: 1. Passenger train derailments, regardless of cause; 2. Collisions with obstructions on the track other than with on-rail equipment or at a rail/ highway grade crossing; 3. Collisions with highway vehicles at rail/highway grade crossing. This permits isolating risks induced by Category I events from overall risks to train occupants (passenger and crew) from train accidents. Characterize hazards or scenarios. The primary inputs to a risk calculation are scenario char- acteristics, specifically the likelihood of the accident, usually quantified as accidents per million train-miles (or per million crossing passes in the case of grade crossings), and accident conse- quences, usually quantified as the number of casualties and financial losses associated with one accident. Measures used to quantify consequences must be aligned with measures used to quan- tify and evaluate risk. Accident likelihood and consequences are typically estimated from his- toric accident data, engineering analysis (for example collision crush and dynamics analysis) and simulations of rail operations. Specific methods used for this analysis are discussed in the model inputs section. Estimate risks. Risk is the product of multiplying frequency, consequences and a level of activ- ity on the system being analyzed, for example train-miles operated over 10 years. It is important
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70 Shared Use of Railroad Infrastructure with Noncompliant Public Transit Rail Vehicles: A Practitioner's Guide to select units of measurement for risk that properly represent the kinds of harm that underlie the motive for the risk analysis. In this case the primary concern is the chance of injuries and fatali- ties among train occupants as a result of train accidents. Thus accident consequences have been estimated in terms of injuries and fatalities per accident; and risk totals are the estimated total injuries and fatalities in FRA-reportable accidents over 10 years of operations of the shared cor- ridor. The longer period of 10 years was chosen because of the limited number of train miles operated each year. With total accident frequency for passenger train operations being about one accident per million train miles and annual train miles on this service being about 200,000, then accident and casualty numbers for each accident scenario will be small and hard to understand, but more meaningful to the reader over 10 years. Risk calculations themselves are carried out in a spreadsheet. The basic calculation is to multi- ply frequency, consequences per accident, and train-miles to obtain an estimate of injuries and fatalities for each accident scenario. Because accident frequency and consequences are affected by traffic density, whether or not freight trains are active on or near the shared-track and no matter the number of train occupants, this calculation is repeated for each of the following categories of passenger train trips: · Peak period trips in the peak direction (i.e., heavily loaded trains); · Peak period trips in the reverse direction; · Trips in the midday period between peak periods; · Early morning and evening trips (which have lower ridership than midday trips); · Freight-exposed midday trips; and · Freight-exposed early morning and evening trips. Freight-exposed means that the trip precedes, follows or passes an active freight train, either en route or actively switching a customer on the shared route. The model can provide for the higher frequency and consequences from collisions involving freight trains. The end product of this calculation is an estimate of risk measured by estimated injuries and fatalities over 10 year's operation of the defined service. Because total ridership in Option 1 is a few percent lower than in the other Options, a direct comparison between estimated fatalities could be slightly misleading, and the more meaningful comparison is between casualties per billion passenger miles. Both measures are calculated in the model. Assess safety adequacy. The final step in the risk analysis is to assess safety adequacy. As indicated earlier, the safety comparison is with Option 1, which represents a currently acceptable operation similar to those on the River LINE and the San Diego Trolley. If risk as measured by injuries and fatalities or injury and fatality rates for the other Options is equal to or less than for Option 1, then the equivalent safety requirement has been satisfied. Practically, however, it is unlikely that FRA and other regulatory authorities would be comfortable with a system that only marginally meets the criterion. Given the uncertainty of input parameters, there will be a significant prob- ability that a marginal system would not meet the criteria. Therefore we look for substantially reduced risk for Options 2, 3, and 4 as compared with Option 1, to be sure that the system will be acceptable. Model inputs. The most important activity and often the most time-consuming is defining all the inputs to the model. Inputs for accident frequencies, consequences, and any risk reduction factors applied to frequencies or consequences for safety improvements must be valid or the analysis results will not be meaningful. The following paragraphs summarize the inputs used in this analysis. Many of the inputs were obtained from the previously referenced FRA study, in which a very similar analysis was performed. All values and quantities cited herein are based on the Task 10 Report. The methodology is transferable when modified to fit project circum- stances. Those factors and considerations can be extrapolated to other projects.