During late 2015, Amtrak conducted Vehicle Track Interaction (VTI) testing over a number of selected test sites in New England and New Jersey. This testing constituted a portion of the “safety case” required of Amtrak by the Federal Railroad Administration (FRA) for certification to raise the maximum authorized speed for high-speed trainsets (on a limited number of segments) to 160 mph.
The specific locations for anticipated 160 mph service include the two existing 150 mph segments in New England (Rhode Island and Western Massachusetts) and possibly the existing 135 mph section in New Jersey. Tests were performed by a specially instrumented Acela Express trainset and were observed and data-recorded by a joint group of FRA, Amtrak, Volpe Center, and Ensco (FRA’s test contractor) engineers and technicians.
On one “downhill” run near Mansfield, Mass., a speed of 171 mph was recorded, exceeded (or at least tying) the reported highest speed of 170 mph previously achieved on the NEC, that by a United Aircraft Turbo-Train in 1966 during that vehicle’s qualifications trials. VTI qualification testing, as well as continual operational monitoring of certain of the test parameters such as vibration, truck hunting and lateral loadings, constitutes a well-prescribed (by FRA) aspect of the NEC’s High Speed Rail Safety Case. VTI is by no means the only engineering factor requiring analysis and testing in the quest for 160 mph authority.
To reach this next speed plateau, FRA requires a comprehensive System Safety analysis, which extends to a wide variety of engineering and operational factors. FRA now places increased emphasis on the formation of a “Safety Case” as a major supplement to prescriptive Safety Standards (e.g., Standards for Positive Train Control or Part “G” of the Track Safety Standards). The required Safety Case is to be developed using the analytical methods of System Safety; Mil STD/SSSTD 882 describes many of these requirements. It should be noted that FRA interest in formation of a Safety Case extends to operations other than HSR, e.g., shared-use operations with light rail, or new-start commuter rail.
Railroads and other industries had long practiced elements of System Safety in their operating and design practices, signal “Lamp Out” protection, for example. As a formal discipline, System Safety has roots in product liability law, beginning with the benchmark case of McPherson v. Buick. This case established that concept of liability for “products” would apply even in the absence of privity of contract. (Privity is the legal term for a close, mutual, or successive relationship to the same right of property or the power to enforce a promise or warranty. It is an important concept in contract law.). This eventually led to a standard by the Society of Automotive Engineers, SAE 882, for System Safety. This standard provides requirements for evaluating “hazards” and quantifying risks associated with those hazards, and outlines methods of risk mitigation.
Risk as used here refers to the mathematical concept of “expected value “of a variable, in this case the expected value of loss or damage. It is a product of the likelihood (probability) of an event occurring and the loss (damage) realized if that event occurs. There is no such thing as “zero” risk. To put a perspective on risk quantification, the probability of a fatality due to railway equipment or operations (i.e. discounting such things as medical conditions) should never exceed more than one in one million and should generally be on the order of one in ten million. Conversely, the probability of a fatality on a Space Shuttle flight had been determined to be approximately one in 400.
Risk may be mitigated by designs or configuration modifications, usage restrictions (as may be included in operating rules or TTSI), test and maintenance practices, and requirements for specialized training/qualifications, e.g., Amtrak’s Class “A” Linemen qualification or FRA Locomotive Engineer licensing.
One of the important components of a rigorous System Safety program is Configuration Management. Where a product, system or “operation” has already been certified as “Safe,” i.e., to an acceptable level of risk, Configuration Management is utilized to evaluate changes. In the case of Safety, these changes may impact the risk profile (other elements of Configuration Management will evaluate cost, life cycle, etc.). In the case of the New England Division of the NEC, only one variable is proposed for the initial change: maximum authorized speed (MAS), from 150 mph to 160 mph. This provides a traceable, step-wise progression from a proven Safe System and Operation at 150 mph to what is anticipated to also be a Safe (at 160 mph) Operation.
Engineering factors to be considered in this analysis include:
• Environmental aerodynamics (crosswinds).
• Train generated aerodynamic effects.
• Track integrity.
• Requirements for a “sealed right-of-way” and how is this to be interpreted.
• Ground waves.
Each of these engineering factors may lead to one or more hazards. Some, but not all, of these hazards realize a change in risk profile with a speed increase and/or a change in location (i.e. operating segment). Those that are of primary interest to the proposed NEC improvements, and an associated change control process, are reviewed below.
There are three general topics:
1. Configuration Management as Applied to Safety: These are discounting cost of change, life cycle impact etc., all of which would normally be included but which is not pertinent to this topic. Change control is best managed by a step-wise process, i.e., one variable at a time. Under this logic, it is not necessary to go back to “first principles” and “reprove Newtonian mechanics.” Start with a “proven to be safe” situation and then control and predict and test-verify the impact of each change. The plan for the NEC improvements is logic-based and consists of:
• Progression of a speed increase at one segment (the initial prototype) with the same vehicle, i.e., change only the speed from 150 to 160 mph for the Acela Express. Operate for a period of, say, six months. The selected segment was Mansfield to Attleboro. Note that FRA requires testing at 5 to 10 mph above desired MAS. Then, repeat for the second segment, i.e., raise MAS for Acela equipment from 150 to 160.
• Expand to the New Jersey high-speed segment (New Jersey High Speed Rail Improvement Program, or NJHSRIP): 135 mph to 160 mph, higher train density and four-track territory. Address any location specific issues. Prove 160 mph.
• Ultimately qualify new trainsets at 160 mph, on the “proven” segments.
• Expand 160 mph with new trainsets to other segments of the NEC, where appropriate.
2. Engineering Factors/General Risk Considerations: Certain risk-related engineering factors are functions of speed. Others are functions of location. Some are both, and some are affected by neither speed or location. The change-control process predicts and verifies these categories. A “think tank,” in an early report whose objective was to identify all risk, noted the possibility of an aircraft crashing on a train! Such a risk, however, is universal to all surface transport and would not be relevant to this Safety Case. Each factor that does, in fact, cause a change in risk requires treatment by design, or operating restrictions, maintenance requirements and/or specialized employee qualifications.
3. Engineering Factors/Specifics: Following is a sampling of factors that are based in the “engineering mechanisms,” and how they might factor into the aforementioned step-wise progression of raising MAS for 150 to 160 mph and/or expanding the number of segments operating at 150 mph or higher (up to 160 mph) speeds:
• Ground waves: As a train progresses along a railway track, waves of disturbed soil propagate in the subgrade in advance of the locomotive. These waves occur well below the ballast and are not to be confused with the vertical wave observed in rail. They advance more slowly in soft subgrade material, e.g., peat or organic clays, than in sandy silt. Such waves may be considered analogous to sound waves propagating in advance of an aircraft. A train whose speed approximates the speed of its ground waves will experience severe instability in the track, potentially resulting in derailment. To further extend the analogy, this phenomena may be likened to an aircraft travelling at the speed of sound. The speed of propagation depends on location and can become an issue in organic subgrades for train speeds as low as 140 mph.
• Track Integrity: There is expected to be no variation with speeds or location for such traditional track “integrity risks” as broken rails or track buckling. Existing methods of mitigation are not expected to vary with the speed change proposed for the NEC test sections. Another aspect of track integrity arises in the New Jersey segment, however, and this relates to track centers. On the former Pennsylvania Railroad main line, nominal centers were 12 feet, 6 inches. However, at some locations, track centers as low as 12 feet, 2 inches were observed on tangent track. Operation of a nominal 10-foot, 6-inch-wide train at 160 mph may, given the required dynamic envelope, be problematic (relative passing speeds of 320 mph with, say, 12 inches clear distance!). Track centers are not currently an FRA inspection parameter,. However, in the future, it may be necessary to register track centers to an “absolute” baseline.
• Environmental Aerodynamics: This pertains primarily to crosswinds, particularly gusts. For high-cant-deficiency curves, such a gust may cause severe unloading of the low rail. This hazard is currently mitigated through operating restrictions and is not expected to be different at higher MAS, since curve speeds will remain controlled by cant deficiency limits even where MAS is raised on adjacent tangent.
• Sealed Corridor: The FRA requires a so-called “sealed corridor” for HSR operation. New-start systems will be constructed in tunnels, on viaducts, or will be otherwise barrier-protected. The application of this doctrine to the NEC is somewhat problematic, and requirements have not been fully articulated by the regulators. One of the requirements for the original, 1970s NECIP (Northeast Corridor Improvement Program) was that the NEC be fully fenced. This was later limited (as a concession to practicality) to fencing of high-hazard areas, e.g., adjacent to schools and parks. A similar approach is in progress for NJHSRIP.
• Train Induced Aerodynamic Effects: This factor is multi-faceted and is much more complex than crosswinds. For speeds above 100 mph, the largest contributor to rolling resistance is aerodynamic drag. This drag on the train causes a compensating disturbance in air that leads to high forces on adjacent objects and personnel. The shape of a high-speed train is a case of form following function; the industrial design (“styling”)is developed by aerodynamic analysis (computational fluid dynamics, or CFD, and wind tunnel testing) to reduce power consumption, minimize pantograph-to-catenary interference, and minimize impact to adjacent objects. Proper shape achieves high efficiency. As an example, the highly aerodynamic New Haven Railroad Comet achieved a speed of 109 mph on the current NEC in 1935. This three-car train developed a mere (diesel) 800 hp as compared to the Acela’s peak 12,400 hp with two power cars.
The challenge lies in the aerodynamics of even a “minimally invasive high speed train” in a busy mixed-use railway. Aerodynamic drag, and therefore the impact on the “close-in” environment, varies as the square of speed. It is worth noting that in tests performed in New England, the forces on an instrumented wayside “dummy” exerted by a passing AEM-7/Amfleet train at 110 mph were observed to be equivalent to those exerted by a passing Acela Express at 125 mph. Likewise, a simple calculation will illustrate that the drag (and hence power consumption) on an Acela at 125 mph is less than that on an NJ Transit ALP-46 or ALP-45DP with Bombardier MultiLevel cars operating at 110 mph.
During 2015, a group of engineers and scientists at the Volpe Institute supported FRA and Amtrak in further analysis into a number of aerodynamics-induced hazards. These included:
• Forces between passing high-speed trains on tight track centers.
• Forces between high-speed trainsets and higher-speed MultiLevel commuter trains and freight trains.
• Flying ballast.
• Forces on wayside objects, e.g., baggage or newspaper vending machines in stations.
• Forces on roadway workers; e.g.; will clearing into an interior out-of-service track be acceptable in four-track territory?
• VTI (Train Specific Response): During Acela’s 160-mph qualification testing in 2015, truck instability occurred at a location in New Jersey. This was traced to a differing rail profile. While this profile was to an acceptable Amtrak standard and did not contribute to truck hunting at a 135 mph, it caused instability at speeds greater than 155 mph. In this case, the derivative mitigation was to not allow this particular rail profile for the 150-mph segments, pending the retirement of the Acela Express and to then retest upon the arrival of the new Alstom high-speed trainsets.
There are other hazards to be evaluated and mitigated in raising NEC speeds to 160 mph. This particular discussion has been limited to some that are based in engineering mechanics. Given political changes in Washington, this may not represent the final word on the path to new trainsets and higher speeds for the NEC. However, it does represent the essential engineering and system safety requirements.
References
“The Turbo Train Story.” Frattasio, Marc J. Shoreline Magazine, Publication of the New Haven Railroad Technical and Historical Society, New Haven Shoreliner, Vol. 29, Issue 2.
Products Liability in a Nutshell, Third Edition. Phillips, J.J. West Publishing Co., 1988.
System Safety Engineering and Management. Roland, H.E., Moriarty, B., and Wiley, 1990.
Esveld, Coenraad. Modern Railway Track, Second Edition. MRT Productions, 2001.
The Handbook of Fluid Dynamics, Second Edition. Johnson, Richard W. CRC Press, 2016.
New Haven Power, Swanberg, Jack. Wayner Publications, 1988.
FURTHER READING:
High Speed Rail in The Northeast: What Next?