Investigation and Mitigation of Insulated Joint Electrical Failure: A Guide (2025)
Chapter: Appendix G: Literature Review
Chapter G-1 Objectives and Background
Objectives
The objectives of TCRP Project D-20, “Investigation and Mitigation of Insulated Joint Electrical Failure,” follow:
- Identify potential causes of insulated joint (IJ) electrical failures, particularly those under high currents resulting from alternating-current (AC) propulsion.
- Identify and document the electrical conditions under which various types of joint failures occur.
- Develop guidelines for maintenance personnel to diagnose IJ electrical failures and determine the best mitigation of the root causes.
- Recommend additional research needed to address root causes of IJ electrical failures.
Background
After the introduction of new vehicle fleets, some electrified railroads noted failures of IJs due to electrical arcing. These railroads distribute the traction power as direct current (DC) using either third-rail or overhead contact wire/catenary (OHC) systems. All return power must return to the originating TPSS. The electrical power is returned to the TPSS using the running rails of the track. This return circuit is called traction power negative return (TPNR) (see Figure G-1). It should be specifically noted that the TPNR is not the same as earth ground—the TPNR systems (running rails) on electrified railways are isolated from earth ground to control stray currents that can damage the adjacent electrically conductive infrastructure.
In the past, many electric locomotives and electric multiple unit (EMU) trains were equipped with DC traction motors. These vehicles used the DC propulsion power provided by the third rail or OHC to drive the traction motors on the locomotives and trains. Where AC propulsion power is provided (typically by OHC), DC traction motors of locomotives and EMUs were still used, with the DC power for the traction motors provided by the onboard conversion (rectification) of the AC power to DC.
Recently introduced power semiconductor technology has allowed the introduction of new vehicle fleets that use AC propulsion systems (traction motors). With this technology, the DC power received at the train is converted to AC onboard the vehicles, allowing for the use of more powerful and reliable AC traction motors that require less maintenance (see Figure G-2, Wikipedia 2025b). A common question is, “Why railways do not simply distribute AC power, thus eliminating the need to invert the DC to AC on trains?” High-level answers include (1) the capital expenditure required to replace existing DC transmission systems on an existing railway is too cost prohibitive and (2) AC power distribution along the trackway is not always possible.
Long Description.
The illustration shows a transit vehicle on the right and a traction power substation on the left connected to the vehicle through traction power through a third rail. A cable through the vehicle wheels to the traction power substation is marked traction power negative return (TPNR) through running rails (back to the substation). A symbol for earth grounding has a negative sign above it, and the text reads, TPNR through running rail is not grounded to earth. Electrical potential exists between running rails and the earth's ground.
Long Description.
The vertical axis is labeled negative volts at the bottom and positive volts at the top. The horizontal axis is labeled times. A set of vertical bands above and below the horizontal axis depicts pulsed direct current (DC), and a sinusoidal curve through these bands depicts the resulting alternating current.
IJs are devices that provide electrical isolation between running rail segments while providing mechanical continuity of the running rails for passing train wheels. This electrical isolation is required primarily for train control track circuits but is also used to separate TPNR sections in the running rails (see Figure G-3).
As train wheels pass over the insulating end post, an electrical connection is made between the two rail ends separated by the IJ. As the last wheel of the train passes over the IJ, the electrical connection provided by the train wheels is broken. If there is a significant difference in electrical potential between the two rail segments (divided by the IJ), arcing may occur (see Figure G-4 and Figure G-5). In some cases, arcing across the IJ is maintained for some time after the train passes the IJ {i.e., until the electrical potential difference at the rail ends is reduced enough to extinguish the arc [i.e., train(s) nearby generating the TPNR current in the running rails leave the area]}.
Arcing is typically not seen where IJs are used solely for the separation of train control track circuits because train control track circuits are of such low voltage that damaging arcing cannot occur. The type of arcing damage investigated in this project is only found on electrified railways where the running rails are used for TPNR. The focus of this project is not the mechanical failure of the IJ assemblies or the deterioration of the insulation of the IJ assemblies—the focus is IJs arcing generated by passing trains on electrified railways.
Chapter G-2 Literature Review
Literature Review
This literature review covers available reports, research, papers, presentations, and other documentation related to IJ failures due to arcing and flashover and related TPNR issues, focusing on IJ arcing that has begun on existing DC systems with new vehicle fleets with AC traction motors. The information found in this literature review was used to develop the questions to be used in Task 2, Industry Survey.
The following list of a large body of work was scanned and reviewed:
- American Railway Engineering Association (AREA) Proceedings (1900–1996)
- American Railway Engineering and Maintenance-of-Way Association (AREMA), Proceedings (1997–2023)
- Manual for Railroad Engineering (AREMA 2025a)
- Communications & Signal Manual (AREMA 2025b)
- Roadmasters and Maintenance of Way Association of America Proceedings (1930–1999)
Long Description.
The exploded view shows the insulating end post with a set of six fastener assembly rails through joint bars and a reinforced epoxy insulating layer to the running rails with insulating bushing between them. The section through bolt shows running rail at the top, followed by the reinforced epoxy insulating layer and joint bars with insulating bushing at the bottom. The fastener assembly is horizontal from right to left. The photo shows a section with two running rails joined together by a joint bar with an insulating end post between them. The joint bar has a set of six fastener assemblies with a reinforced epoxy insulating layer between the joint bar and rails.
Long Description.
The photos are marked as follows. 1. No notable sparking as the second-to-last axle passes over the IJ end post. The direction of the train movement is to the right. 2. Initial sparking as the last axle passes over the IJ end post. The direction of the train movement is to the right. 3. Expanding arc flash at IJ as the last wheel passes over IJ. The direction of the train movement is to the right. 4. Spark spray from melted rail. The direction of the train movement is to the right. A photo on the left shows a rail joint with resulting IJ damage.
Long Description.
The illustration is as follows. 1. Trailing Truck Approaches IJ. At this point, there may be little potential difference across the IJ, or the potential difference is passing through the negative return system on the car. The train itself is likely generating the TPNR load in the running rails (and potential difference across IJ). Notable arcing is typically not seen on the leading axles of a train. 2. Trailing Truck Bridges End Post of the IJ. Any potential difference across the IJ, or the potential difference is passing through the negative return system on the car truck. Notable arcing is typically not seen on the leading axles of a train. 3. Trailing Axle Breaks Contact at IJ End Post. As the last wheel breaks contact with one of the rails, it effectively acts as an opening contact on a switch. If there is sufficient potential difference across the IJ, arcing can occur. Under some conditions, arcing across the IJ end post may be sustained for some time after the wheel passes until the potential difference in the two rail ends is reduced or eliminated.
- Electric Railway Journal (1884–1908)
- The Street Railway Journal (1908–1931)
- American Transit Engineering Association (ATEA)/American Electric Railway Engineering Association Manual Proceedings (1910–1946)
- AEREA/ATEA “Standards and Recommendations Covering Power (Division D), Rolling Stock (Division E), Ways and Structures (Division W).” (ATEA Manual), 1941.
- NTSB railroad accident investigations
- Interstate Commerce Commission, Investigations of Railroad Accidents (1911–1993)
- IEEE publications
- Association of American Railroads research reports and technology digests
- The Permanent Way Institution (PWI) publications
- U.S. DOT reports and publications
- TCRP publications
- National Electrical Manufacturers Association publications
- ITE publications
- ASCE publications
- International Union of Railways publications
- International Journal of Rail Transportation publications
- Journal of Railway Transportation and Technology
- The Korean Society for Railway, Journal of the Korean Society for Railway
- Railway Technical Research Institute publications
- Research Gate
- Google Scholar
- General World Wide Web searches
For online and electronically available sources, the following search terms were used:
- Insulated rail joint
- Insulated joint
- Insulating rail joint
- Insulating joint
- Arcing flash
- Impedance
- Negative return
- Flashover insulated joints (rail)
- Arcing insulated joints (rail)
- Arcing traction motor (rail)
- Flash over traction motor (rail)
- Traction motor stray current (rail)
- Spark theory
- Spark generation
Literature Review Results
General
Only four research threads directly related to IJ arcing were found. One thread is a study for Metro-North Railroad (MNR) and Long Island Rail Road (LIRR) (Swartley et al. 2013) detailing arcing at IJs on railroads with DC traction systems. The second thread has many research reports related to IJ arcing on Chinese railways, however, all the reports describe IJ arcing on AC traction systems. This research thread is discussed separately below. A third thread is an unpublished internal study on a DC traction transit system. MxV Rail was denied permission to publish or
directly reference the report but was given permission to use generalized information from the report, stripped of references to the originating source. The fourth thread provides references in Transport for NSW engineering documents related to the staggering of IJs on adjacent rails to provide overlap of the TPNR rails (Transport for NSW 2019). Some references were found in the AREMA MRE and AREMA C&S Manual related to staggering IJs on electrified railways but little information is provided regarding the reasoning behind the decision to stagger IJs.
Some of the solutions proposed in the LIRR/MNR presentation (Swartley et al. 2013) include improvements to the TPNR system such as additional cross bonding (additional electrical cable connection between adjacent running rails), additional impedance bonds (electrical connections used at IJs that allow TPNR to bypass IJs and block train control track circuit signals at the same time), increased capacity impedance bonds, addition of a dedicated TPNR rail (fourth rail), electrical and mechanical shunting of IJs (as trains pass), long-lap IJs (see Figure G-6, Davis et al. 2007), and graduated resistance IJs. The unpublished report noted previously mentioned the implementation of rail-to-rail cross bonds at IJs where single-rail track circuits and TPNR rails are transposed as a successful mitigation. A common link in all the related information found appears to be deficient TPNR for the existing conditions that create a potential electrical difference between the two rail ends at IJs. In all cases, IJ arcing can be traced to either the design of the TPNR system, insufficient design integration of vehicles/traction power/track/train control, or changes made to one or more components on existing systems.
The literature does not appear to support the relationship between the IJ arcing phenomenon and the mechanical failure of IJs or the deterioration of the insulation within IJs. Damage to IJs where arcing occurs appears to be a direct result of the arcing and not a failure of the IJ. This philosophy was used to guide the Industry Questionnaire and Industry Interviews. Although some of the suggested mitigations might improve the ability of IJs to resist arcing, without mitigating the underlying issues, arcing may still occur.
Chinese Railways Research
A large amount of work has been done related to IJ arcing on high-speed railways in China, and each report describes IJ arcing on AC traction systems. These AC systems differ from what has been found so far in the literature review, namely, the AC traction power return (TPR) is distributed across multiple cars and fed back into the track at discrete wheels (Cheng, Liu, and Huang 2017), thereby creating issues for the TPR at IJs because electrical bridging over the IJs can extend the entire length of the train. On common DC traction systems, the power is typically received
and returned at each truck or car and is not train-lined, likely reducing the electrical bridging of the TPNR over IJs. The mitigation proposed for IJ arcing in this thread included modifications to the TPNR system (Bi, Zhao, and Zhang 2013; Yang et al. 2013; Xiao et al. 2013; Bi et al. 2015; Yang et al. 2016; Cheng, Liu, and Huang 2017; Ji et al. 2020; Bo 2022), improved IJs (Yang et al. 2013), and intelligent switching (connecting rail ends) of TPR across IJs (Xiao et al. 2013).
“Research and Analysis on Contact Resistance of Wheel and Insulated Rail Joint in High-Speed Railway Stations” (Li et al. 2023) indicates additional information of interest including arc temperature compared to amperage across the IJ (e.g., rail melting temperature) and the influence of IJ resistance with changes in end-post thickness, train speed, and axle loads.
The publications listed below were reviewed as part of the research thread. The titles of these reports indicate information that will likely be directly useful in this research.
- “Transient Analysis of Electric Arc Burning at Insulated Rail Joints in High-Speed Railway Stations Based on State-Space Modeling” (Cheng, Liu, and Huang 2017)
- “Solution for Burning Loss of Insulation Sections in High-Speed Railway Stations” (Bi et al. 2015)
- “Analysis on the Causes of Track Insulation Joint Burnout in Electrified Sections and Its Countermeasures” (Bo 2022)
- “Analysis of Potential Difference of Mechanical Insulating Joint in High-Speed Railway Station” (Bi, Zhao, and Zhang 2013)
- “Study and Simulation Tests of Burning Damage to Insulation Joints and Rails in High-Speed Railway Stations” (Yang et al. 2013)
- “Solution to Reduction of Potential Difference on Both Ends of Insulation Joint Based on Simulation Model Traction Power Supply System in Typical Station of High-Speed Railway” (Yang et al. 2016)
- “Influence Mechanism of the Mobile Grounding Reflux on the ‘Wheel-Rail’ Rolling Arc at Insulated Joints of High-Speed Railway” (Xiao et al. 2013)
- “Research and Analysis on Contact Resistance of Wheel and Insulated Rail Joint in High-Speed Railway Stations” (Li et al. 2023)
Federal Railroad Incident Investigations
Searches were performed in federal railroad accident databases for the NTSB (2010–present), FRA (1975–present), and Interstate Commerce Commission railroad accident investigations data (1911–1994). All incidents that involved IJs were related to mechanical failures of IJs or the rail at IJs (NTSB 2005a, NTSB 2005b) and not electrical arcing.
There are some federal reports related to electrical arcing; however, all are related to arcing and resulting fires primarily related to water intrusion in tunnels and TPNR faults at rail fasteners. One NTSB incident investigation (NTSB 2016) ultimately resulted in a special investigation by FTA (FTA 2016). No federal reports or investigations related to IJ arcing and pertinent to this guide were found.
AREMA Proceedings
AREMA Proceedings and its predecessor organization, the American Railway Engineering Association Proceedings from 1900 through 2023 were reviewed. Another AREMA predecessor organizationʼs proceedings, the Roadmasters and Maintenance of Way Association Proceedings from 1933 through 1997, were also reviewed. No references related to IJ arcing were found; however, the following references related to TPNR, stray currents, and arcing:
- “Contact Rails Rail Bonding” (AREA 1977)
- “Signal Compatibility with Alternating Current Railway Electrification” (Tufts 1981)
- Manual Recommendation Committee 33—Electrical Energy Utilization (AREA 1982)
- “Rail Assets Related Innovations from the International Railway Community with Potential for use in North American Railways” (Lentini 2020)
- “‘Blue Book’ on Inductive Coordination Task Force Progress Report” (Frazier, Logan, and Cramer 2001)
- “Transient AC Induction Environments for Signal Systems” (Perala, Kawalko, and Keefe 2000)
- “A Design-Build Project in AC Electrification from a Wayside Engineering Perspective” (French 2022)
- “Minimally Invasive Measurement of the Electrical Properties of Railway Track Under Operating Conditions” (Landau and Kraft 2022)
- “Prevention of Stray Current by the Maintenance-of-Way” (Kale and Sanders 2000)
AREMA Manual for Railroad Engineering
While no information related to IJ arcing was found in the 2024 AREMA MRE, Chapter 33—Electrical Energy Utilization does include a specific section: “Part 7—Traction Power Electrification System Grounding and Bonding.”
AREMA C&S Manual
The 2024 AREMA Communications and Signals Manual (AREMA C&S Manual), formerly the Communications and Signal Division of the Association of American Railroads (AAR) American Railway Signaling Principles and Practices, does not include any information directly related to IJ arcing. However, Part 2.1.20C—Recommended Insulated Joint for Electric Operation Territory includes references to staggered (overlapped) IJs on opposite rails on the same track, including at impedance bonds; however, no reasoning or explanation for the IJ stagger is provided other than “importance due to return propulsion current, joint stagger shall be made so that propulsion rails overlap.”
The Street Railway Journal/Electric Railway Journal
The periodicals The Street Railway Journal (from 1884 through 1908) and its successor, Electric Railway Journal (from 1908 through 1931), were also searched for information. These journals go back to the beginnings of electrified railways and include advertisements and articles related to horse husbandry for horse-drawn railways that had yet to electrify (see Figure G-7, The Street Railway Journal 1885). From the information in various early articles, it appears that as the horse railways were initially electrified, many relied on unbonded rail joints and earth ground for TPNR back to originating traction power substations (TPSSs). Large amounts of information related to TPNR practices, rail bonding and bonding maintenance, and the deleterious effects of stray currents from insufficient TPNR systems are included. No specific information directly related to arcing at IJs was found, but the issues with electrical potential differences were recognized. One example is a report of a lawsuit by a person who claimed his horse ran out of control allegedly due to being shocked when the horse touched the rails near an IJ (Electric Railway Journal 1923). There are many articles related to stray currents, damage to adjacent buried pipelines and their mitigations, and briefs on the resulting legal actions and legislation. Beginning in the late 1920s, many articles reported public complaints of radio frequency interference caused by arcing at rail joints with poor bonding and pantograph/trolley pole arcing on catenary, including articles related to wheel bearing damage from arcing (Angstrom 1921). Early electric vehicles relied on TPNR transmission through wheel bearings to the wheels and running rails, whereas modern vehicles use more reliable slip-ring systems that allow the TPNR to bypass bearings.
Long Description.
The advertisement shows a text paragraph on the left and two men grooming a horse using Pennington's grooming machine on the right.
American Electric Railway Engineering Association/American Transit Engineering Association Proceedings
No specific information related to IJ arcing was found in the American Electric Railway Engineering Association (AEREA)/American Transit Engineering Association (ATEA) Proceedings from 1910 through 1946. These proceedings were found to contain many presentations and papers related to rail joint bonding strategies, installation, and maintenance.
American Transit Engineering Association Manual
No specific information related to IJ arcing was found in the ATEA Manual. However, the ATEA Manual includes Section D122-37 – Bonding for Surface Lines that has information related to the installation and maintenance of rail joint bonds for TPNR.
Railway Technical Research Institute
Two papers of interest from Railway Technical Research Institute were reviewed for their relationship to TPNR: “Detecting High Resistance Grounding Faults in DC Electric Railways Using High Frequency Current Injection” (Okui 2004) and “Calculation of the Current Distribution of Return Circuit at the Station” (Terada et al. 2016). Neither contained information related to IJ arcing.
IEEE Publications
A search of IEEE publications yielded the initial lead to the thread related to the Chinese research on IJ arcing. The IEEE also provides access to Arc Flash IE and Iarc calculators (IEEE 2019). This resource may be used in future work on this project to aid in the determination of potential differential levels that can lead to destructive arcing at IJs.
Association of American Railroads Publications
All the published AAR research reports (R-Reports) and technology digests (TDs) were reviewed. Even though no reports related to IJ arcing were found, there are numerous TDs available that detail research related to efforts to develop longer-lasting IJs that can withstand modern heavy axle loads (HAL). Since the related R-Reports include only details summarized in these TDs, and the TDs are directly available for public access, the authors focused on the TDs in this literature review. While it is likely that the IJ arcing being investigated in this effort is not related to mechanical failures, some of the enhanced IJ designs described in these TDs may have some application for mitigating IJ arcing. The related TDs found are the following:
- “Bonded Insulated Joint Performance in Mainline Track” (Davis, Collard, and Guillen 2004)
- “Performance Evaluation of Bonded Insulated Joints” (Akhtar, Davis, and Read 2005)
- “Development of an Improved Performance Bonded Insulated Joint for HAL Service” (Akhtar and Davis 2005)
- “Analysis of Conventional and Tapered Bonded Insulated Rail Joints” (Davis et al. 2005)
- “Measurement of Load Environment and Performance of Insulated Joints at Western Mega Site” (Li et al. 2006)
- “Preliminary Results of Prototype Insulated Joint Tests at the Facility for Accelerated Service Testing” (Akhtar and Davis 2007)
- “Evaluation of Improved Designs for Bonded Insulated Joints in HAL Service” (Davis et al. 2007)
- “Rail Joint Installation and Maintenance Recommended Practices” (Davis, Akhtar, and Read 2008)
- “Prototype Next Generation Insulated Joints” (Davis and Akhtar 2010a)
- “An Update on Revenue Service Evaluation of Premium Insulated Joints” (Davis and Akhtar 2010b)
- “Establishment of a Heavy Axle Load Northern Mega Site” (Davis et al. 2013)
- “Premium and Next Generation Insulated Joints in Heavy Axle Load Revenue Service” (Baillargeon et al. 2015)
- “In-Field Implementation of Impedance-Based Structural Health Monitoring for Insulated Rail Joints” (Albakri et al. 2017)
- “Evaluation of Premium Insulated Rail Joint Designs in Revenue Service Testing” (Davis, Pinney, and Alishio 2019c)
Permanent Way Institution
The Permanent Way Institution (PWI) is a worldwide railroad maintenance-of-way organization, headquartered in England. A major focus of the PWI is disseminating practical hands-on information and current practices for railroad permanent way practitioners. No specific PWI publications, including PWI Journal articles from 1884 to present, were found related to IJ arcing.
Transport for New South Wales
Multiple engineering documents that include information on signaling, TPNR design, TPNR bonding, and IJ layouts are available at the Transport for New South Wales (NSW) at their Transport Standards Portal and in Engineering Guideline Engineering Specification, Signals,
Construction Specification—Traction Return, Track Circuits, and Bonding. SPG 0709 provides direction on the field layout of IJs to minimize arcing (see Figure G-8, Transport for NSW 2019).
Publications Related to Electrical Arcing
IJ arcing appears to be a symptom of other underlying issues that create electrical potential differences across the end posts of IJs. However, the symptoms act very much like the arcing that occurs on high-voltage electrical switches. Electrical switch arcing is something that has been well researched since the beginning of the industrialization of electricity. The potential differences that can generate arcing and the quenching of those arcs are reasonably well understood; however, further research is ongoing. A practical understanding of basic arcing theory will be important in the diagnosis of IJ arcing issues. MxV Rail found the following texts useful in describing the arcing phenomenon:
- The Mechanism of the Electric Spark (Loeb and Meek 1941)
- The Electric Arc (Somerville 1959)
- Electric Contacts: Theory and Application (Holm 2013)
- Electrical Contacts: Principles and Applications (Timsit 2017)
- Electrical Contacts: Scientific Fundamentals (Timsit 2013)
Publications Related to Electric Arc Welding
The IJ arcing phenomena appears to have similarities to electric arc welding. A practical understanding of certain basic electric arc welding principles, including metal flow and metal disposition, will be important in the diagnosis of IJ arcing issues, particularly the visual identification of the direction of current flow based on the condition of rail ends at IJs. MxV Rail found the following texts useful in describing electric arc welding theory:
- Arc Welding Handbook (Holslag 1924)
- Arc Welding Manual (General Electric Company 1929)
Long Description.
The illustration shows two tracks with a crossover including traction (TPNR) rail, signal rails, and insulated rail joints. The preferred arrangement with small overlap is at the top, with overlaps exaggerated to show the principle. The preferred arrangement with a small overlap of traction (TPNR) rails is at the bottom.
- Welding Design, Procedures, and Inspection (U.S. Department of the Army 1985)
- Introduction to the Physical Metallurgy of Welding (Easterling 1992)
Other Publications
During the literature review, a large body of publications were reviewed. While the publications listed below do not relate to IJ arcing directly, they do contain useful information related to traction power return circuits and TPNR design.
- Modern Practice in the Construction and Maintenance of Rail Joints and Bonds in Electric Railways (Shepard 1916)
- Transit Engineering Principles and Practice (Tuthill 1935)
- TCRP Research Report 212: Stray Current Control of Direct Current-Powered Rail Transit Systems: A Guidebook (Flounders and Memon 2020)
- TCRP Report 155: Track Design Handbook for Light Rail Transit, Second Edition (Parsons Brinckerhoff, Inc., Metro Tech Consulting Services, Engineering & Architecture, P.C., Track Guy Consultants, and Wilson, Ihrig, & Associates, Inc. 2012)
Chapter G-3 Synthesis of Results and Conclusions
The reviewed sources consistently indicate that limitations or deficiencies in TPNR systems often contribute to IJ arcing issues. IJ arcing is not typically caused by the IJs, but changes in the IJ design and layout may aid in mitigating arcing. In DC systems, particularly those adapted for vehicles with AC traction motors, these limitations are frequently attributed to inadequate bonding or insufficient TPNR capacity to handle increased power demands. The following key themes were gathered from the literature.
TPNR System Limitations
IJ arcing on DC traction systems (with vehicles using either DC or AC traction motors) often stems from insufficient TPNR configurations. Changes to a DC electrified railway, such as vehicles with higher load demands, longer trains, increased traffic densities, may overload the TPNR system or cause excessive differences in electrical potential at IJs that can lead to arcing. Solutions, such as additional impedance bonds, increased impedance bond capacity, train speed/acceleration limitations, modification of the on-train propulsion systems, dynamic or passive IJ shunting, additional cross bonding, use of electric fourth rail for TPNR, and replacement of train control system with systems that do not require IJs, have been proposed in the literature reviewed, but some require extensive system modifications that may not be economically feasible or could negatively affect the performance of the train control systems.
IJ Stagger
On electrified railways, “square” IJ configurations where the IJ end posts are installed directly across from each other on the same track, including at impedance bonds, are common. Within turnouts and crossovers and other locations with single-rail TPNR, IJs may also be arbitrarily square, or arbitrarily staggered, without ensuring the rails carrying the TPNR are not overlapped. Improperly overlapped IJs will create a gap in the TPNR path and preclude the TPNR from passing through the train axles when passing over IJs, which can increase the possibility of IJ arcing. AREMA publications recommend staggered IJs for electric railways but provide no information
or guidance as to why; however, the Transport for NSW recommends staggered IJs (overlapping TPNR rails) to reduce IJ arcing (2019).
On-Train Distribution of Power and TPNR
The distribution of the traction power and TPNR within trains can create situations where IJ arcing can occur. The power received by a train must return to the TPSS that supplies the power to complete the electrical circuit. In situations where the traction power is drawn from one TPSS, and the train passes over an IJ that separates or impedes the TPNR from that TPSS, arcing can occur. The possibility of IJ arcing increase where the traction power or TPNR is shared or distributed across multiple trucks and even more when “train-lined” across multiple vehicles. AC systems on high-speed railways, such as those in China, present unique challenges and may require innovative solutions like intelligent switching to dynamically connect rail ends at IJs as train pass.
IJ Material and Design Innovations
Innovations in IJ materials and structural designs, such as long-lap and graduated resistance IJs have been proposed. Long-lap IJs, where the break in the rail and end posts cross the rail in a long diagonal, were developed to address IJ structural failures from HAL by distributing the impact loads over a longer distance along the rail. The materials technology for graduated resistance IJs that have been suggested as a solution currently does not exist. Studies also suggest that thicker end posts and alternative IJ insulating configurations and layouts may improve IJ resilience to arcing.
Improvements in IJ design may aid in reducing IJ arcing but will not address the underlying problems that create the potential for arcing. However, some improvements or changes that increase the resistance at IJs or aid in improving the breaking of the electrical contact with the wheels may be useful to mitigate the IJ failures resulting from TPNR or vehicle design issues that are otherwise not economically feasible to directly address.
Historical Publications
The Street Railway Journal, Electric Railway Journal, AEREA/ATEA Proceedings, and the ATEA Manual did not yield specific information directly related to IJ arcing but provided useful insight and context concerning TPNR issues.
Electrical Switch Arcing and Arc Welding Publications
Publications related to electrical switch contact theory, spark extinguishment, and electric arc welding are useful in describing the mechanics of IJ arcing such as estimating voltage, amperage, and current flow related to IJ arcing events.
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