Rail Safety Technology

R​ail safety technologies protect passengers, railroad employees and communities by helping to prevent collisions, derailments, equipment failures and their resulting deaths and injuries. When equipment fails, people make mistakes, or operating conditions change, dangerous conditions can develop. Rail safety technologies act as an extra layer of protection against these conditions to prevent injuries and save lives. 

The National Transportation Safety Board (NTSB) has repeatedly identified how slow development or adoption of safety technology has contributed to preventable accidents. Several safety technologies are not yet fully mature or used everywhere they could reduce or eliminate safety risks, including 

  • Positive train control (PTC) 
  • Transmission-based train control (TBTC) 
  • Safety technology for roadway maintenance machines 
  • Head- and end-of-train communications 
  • Equipment monitoring systems such as wayside detectors 
  • Inward- and outward-facing cameras 

NTSB’s Role in Advancing Rail Safety Technology

​​Since the fatal train collision in 1969, where NTSB first recommended a technology like today’s positive train control systems, to more recent recommendations for all on-track roadway maintenance machines to be equipped with collision avoidance systems, NTSB investigations consistently show that safety technology can prevent or mitigate the severity of rail accidents and that delayed implementation of available safety technologies contribute to preventable accidents, deaths and serious injuries year over year. ​​

Rail Safety Technologies

Positive Train Control (PTC) for Freight and Commuter Rail

<p>​On August 20, 1969, two Penn Central commuter trains collided head-on near Darien, Connecticut, killing four and injuring 43. That tragedy began the NTSB&#39;s call for development and implementation of positive train control (PTC) systems. The NTSB issued almost 50 PTC-related safety recommendations before PTC was fully implemented by the Class 1 railroads in 2020—50 years later.&#160;<br/></p><p>Positive train control is a GPS-based system designed to prevent train-to-train collisions, over-speed derailments, incursions into established work zone limits and the movement of a train through a switch left in the wrong position. PTC is required on tracks with regularly scheduled intercity or commuter passenger rail service and Class I railroad main lines carrying poison- or toxic-by-inhalation hazardous materials.&#160;<br/></p><p>Full implementation of PTC across the nation’s rail system has undoubtedly improved safety. However, NTSB investigations have also identified gaps in safety performance with existing PTC systems, in the following areas: ​</p><p><strong>Restricted speed operations&#160;</strong></p><ul><li>When trains operate at restricted speed, safety depends heavily on human performance. Existing PTC systems generally cannot prevent collisions that occur under these operating conditions.&#160;</li></ul><p rtenodeid="3"><strong>End of track collisions</strong></p><ul><li>Regulatory exceptions mean PTC is not required in some passenger terminal environments. As a result, current systems may not prevent all end-of-track accidents.&#160;</li></ul><p rtenodeid="4"><strong>Switching mode</strong></p><ul><li>Some switching moves require railroads to temporarily suspend portions of PTC protection. These suspensions create safety vulnerabilities until train protection functions are restored.&#160;</li></ul><p rtenodeid="5"><strong>Work zone protection&#160;</strong></p><ul><li>Although PTC can help prevent trains from entering protected work zones, many systems still rely on a single individual to establish or remove protections, meaning one error can leave a work zone unprotected. Additional safeguards could further improve safety.&#160;<br/></li></ul><p>The NTSB report, Beyond Full Implementation: Next Steps in Positive Train Control explores accidents with these safety gaps.&#160;<br/></p>

Transmission-Based Train Control (TBTC) for Rail Transit

<p>​Transmission-based train control (TBTC) is a safety system designed to automatically slow down or stop a rail transit train before certain types of accidents occur. Like PTC, TBTC can reduce the risk of train collisions and overspeed events&#160;<br/></p><p></p><p>through continuous monitoring and enforcement of train movements. Although both systems provide critical safety functions, they are generally implemented in different railroad operating environments.<br/></p><p> <strong>PTC</strong> is primarily deployed on freight railroads and intercity and commuter passenger rail systems. PTC is designed to prevent:<br/></p><ul><li>​Train-to-train collisions</li><li>Overspeed derailments</li><li>Unauthorized incursions into established roadway worker protection zones</li><li>Train movements through improperly aligned switches<br/>​<span id="ms-rterangecursor-start" rtenodeid="1"></span><span id="ms-rterangecursor-end"></span><br/></li> <strong>TBTC</strong> is typically used on fixed-guideway rail transit and metro systems operating in high-density urban environments. TBTC provides continuous train position and speed monitoring to: <ul><li>​Maintain safe train separation</li><li>Prevent train-to-train collisions</li><li>Enforce speed restrictions<br/></li></ul><p>The NTSB has issued safety recommendations since 1995 advocating the implementation of advanced train control technologies, such as TBTC, capable of preventing train collisions and overspeed accidents on rail transit systems. While Congress mandated implementation of PTC on certain freight and passenger railroads through the Rail Safety Improvement Act of 2008, no comparable federal requirement exists for the installation of TBTC or equivalent train control technology on rail transit systems regulated by the Federal Transit Administration (FTA).<br/></p><p></p><p> <strong>​Why it Matters&#160;</strong></p><p>TBTC provides rail transit and subway systems with many of the same protections that PTC provides on commuter and freight rail systems.</p><p> <br/> </p></ul>

Head- and End-of-Train Communications Technology

<p>​​Head-of-train (HTD) and end-of-train (ETD) devices are electronic systems that communicate between the front and rear of a train to monitor brake system status and support emergency braking. During an emergency brake application, the HTD in the lead locomotive sends a radio signal to the ETD at the rear of the train, allowing the brake pipe, which spans the length of the train, to be vented from both ends of the train and improve braking effectiveness.&#160;<br/></p><p>Emergency brake commands can be transmitted in two ways:&#160;&#160;<br/></p><ol><li>​A reduction in brake pipe air pressure that propagates through the train.&#160; &#160;</li><li>Radio communication between HTD and ETD.&#160;&#160;<br/></li></ol><p>Together, these methods provide redundancy to help ensure emergency braking can occur even if one communication method is degraded or unavailable.&#160;&#160;<br/></p><p>The importance of this redundancy was highlighted by the October 4, 2018, freight train collision near Granite Canyon, Wyoming. The NTSB determined that the accident resulted from an air brake failure caused by a restriction in the brake pipe and the failure of the ETD to respond to an emergency brake command. Because of the way the communication protocols on the accident train were set up, the crew would not receive a notification that the HTD and ETD had lost contact until they were unable to communicate for 16 minutes and 30 seconds, as allowed by federal regulations. The HTD was also not configured to keep transmitting an emergency braking command until the ETD confirmed receipt and initiated emergency braking. The investigation also identified communication limitations caused by train length, track curvature, and terrain.&#160;&#160;<br/></p><p>In response, the NTSB issued safety recommendations calling for more robust HTD and ETD communication protocols, repeated transmission of emergency brake commands until receipt is confirmed, and actions to identify and mitigate locations where communications between devices may be unreliable.&#160;&#160;</p>

Safety Technology for Roadway Maintenance Machines

<p>The NTSB has investigated multiple accidents involving workers being struck and killed by roadway maintenance machines in work zones. Technologies such as operator presence controls and collision warning and avoidance systems can detect people approaching equipment, warn the operators, and actively intervene to prevent or mitigate an accident.&#160;<br/></p><p>The NTSB has issued safety recommendations urging that these systems be installed on roadway maintenance machines across the nation to detect people, objects or machines and automatically stop a machine when a collision is imminent, and to prevent unexpected movements when an operator is not at the controls.&#160; &#160;<br/></p>

Wayside Detection Systems

<p>​Wayside detection systems are installed on or near railroad tracks to monitor passing trains. These systems automatically scan components, such as wheels and bearings, to identify developing mechanical problems before they become safety hazards.&#160;<br/></p><p>​​When a system detects a problem, it sends an alert to train crews or dispatchers, who can take action before equipment fails. One of the most common types of wayside defect detection systems is the hot bearing detector, a type of sensor that measures bearing temperatures to alert crews to overheating.<br/></p><p>Overheated wheel bearings can lead to derailments. Hot bearing detectors help identify failing bearings early, reducing the risk of a derailment or other accident.&#160;<br/></p><p>The February 3, 2023, train derailment in East Palestine, Ohio, demonstrated the catastrophic consequence of an unaddressed overheated bearing. In this accident, a series of hot bearing detectors identified unusually high temperatures on a bearing and eventually triggered an alarm, but the combination of alarm thresholds and distance between detectors prevented the system from alerting the crew before the overheated bearing caused an axle separation. The axle separation led to the derailment, releases of hazardous materials, and fires.&#160;<br/></p><p>The NTSB investigation found that improvements to wayside detection system technology and operation could enhance safety. The NTSB concluded that federal requirements for installing, inspecting, and maintaining these systems would improve their reliability and reduce risk.<br/></p><p>Railroads install and operate these systems voluntarily. Although all Class I railroads use them, there are no federal regulations requiring or standardizing their use. The Association of American Railroads (AAR) provides some guidance on the use of wayside bearing defect detection, but individual railroads vary in their approaches.<br/></p>

Onboard Detection Systems

​​Onboard detection systems use sensors mounted on locomotives and railcars to continuously monitor track conditions and the interaction between train wheels and rails. These systems can identify track geometry issues, deteriorating track conditions, wheel and rail impacts, ride quality concerns and defects such as battered and broken rail joints.&#160;<div><br/><p>The NTSB highlighted the safety benefits of these technologies following the September 25, 2021, derailment of a passenger train carrying 165 passengers and crewmembers near Joplin, Montana. The NTSB investigation found that autonomous track monitoring technologies, including vehicle-track interaction (VTI) systems, can detect signs of track deterioration in real time and provide railroads with earlier warning of developing safety risks. ​</p></div>

Onboard Video and Audio Recorders

​​Crash- and fire-protected inward- and outward-facing audio and image recorders provide critical information about the events leading up to and during an accident.&#160;<p>The NTSB has long advocated for the installation of audio and image recorders in locomotives because of their value for both accident investigation and accident prevention. Beyond helping investigators reconstruct events, recorder data can help railroads identify unsafe practices, evaluate operating procedures, and improve training programs before an accident occurs.&#160;&#160;<br/></p><p>For more than a decade, the NTSB has recommended that federal regulators require inward- and outward-facing audio and image recorders on both passenger and freight locomotives. These recommendations stem from numerous accident investigations in which NTSB determined recorder data would have provided critical information that was unavailable because train operators were killed, seriously injured or unable to recall key details leading up to the accident.<br/></p>

Related Investigations By Rail Safety Technologies

Positive Train Control 

​Transmission-Based Train Control (TBTC) for Rail Transit​​

Head- and End-of Train Communications Technology 

Safety Technology for Roadway Maintenance Machines​

Wayside and Onboard Detection Systems​

Onboard Video, and Audio Records

Key Safety Recommendations

​​​​​Open Recommendations Representing Critical Safety Priorities 

To the Secretary of Transportation:  

  • ​R-24-001: Require the Federal Railroad Administration to issue regulations for inward-facing recorders that include image and audio recordings as recommended by the National Transportation Safety Board in R-24-10 and R‑24‑11. If necessary, obtain legislative authority to act on this recommendation.  

​To the Federal Railroad Administration: 

  • R-20-11 Require new roadway maintenance machines to be equipped with operator presence controls to prevent unintended movement and protect workers on and around the machines.  
  • R-20-28 Revise Title 49 Cod​e of Federal Regulations Part 232 to require more frequent communication checks between a head-of-train device and an end-of-train device. 
  • R-20-29 Require that the emergency brake signal transmission is repeated until received by the end-of-train device. 
  • R-25-07 Require on-track roadway maintenance machines with booms or other movable extensions to be equipped with a 360° people detection system that covers the length of the boom or extension in all directions and alerts operators when people are within an unsafe proximity. 
  • R-25-06 Require all on-track roadway maintenance machines (RMMs) to be equipped with collision avoidance systems that can detect people, objects, or other machines on the ground and automatically stop the RMM before a collision. 
  • R-24-011 Require that railroads regularly review and use in-cab audio and image recordings (with appropriate limitations on public release), in conjunction with other performance data, to verify that train crew actions are in accordance with rules and procedures that are essential to safety. If necessary, obtain legislative authority to act on this recommendation. 
  • R-24-010 Require the installation, in all controlling locomotive cabs and cab car operating compartments, of crash- and fire-protected inward- and outward-facing audio and image recorders capable of providing recordings to verify that train crew actions are in accordance with rules and procedures that are essential to safety as well as train operating conditions. The devices should have a minimum 12-hour continuous recording capability with recordings that are easily accessible for review, with appropriate limitations on public release, for the investigation of accidents or for use by management in carrying out efficiency testing and systemwide performance monitoring programs. 
  • R-24-005 Use the results of the research described in R-24-2 to develop and establish rules governing railroads’ operational responses to bearing alerts and alarms. 
  • R-24-004 Establish requirements for the installation, inspection, and maintenance of wayside bearing defect detectors to protect the reliability of these devices and improve the safety of railroad operations. 
  • R-24-003 Use the results of the research described in R-24-2 to develop and establish minimum requirements for bearing defect detection systems, including criteria for bearing alert and alarm thresholds and maximum distances between wayside detectors. 
  • R-24-002 Research the effectiveness of current bearing defect detection systems, identify minimum standards to protect railroad personnel and the public, and make public the results of this research. 
  • R-23-02 Establish interoperability requirements among railroads to implement a process in which a predetermined critical alert from a vehicle/track interaction system would require an immediate slow order that remains in place until a walking inspection is performed and, if needed, subsequent repairs are complete. 
  • R-12-03 Require that safety management systems and the associated key principles (including top-down ownership and policies, analysis of operational incidents and accidents, hazard identification and risk management, prevention and mitigation programs, and continuous evaluation and improvement programs) be incorporated into railroads’ risk reduction programs required by Public Law 110-432, Rail Safety Improvement Act of 2008, enacted October 16, 2008.  

To the Federal Transit Administration:
  • R-17-013 Require the installation, in all controlling locomotive cabs and cab car operating compartments, of crash- and fire-protected inward- and outward-facing audio and image recorders capable of providing recordings to verify train crew actions and train operating conditions. The devices should have a minimum 12-hour continuous recording capability with recordings that are easily accessible for review, with appropriate limitations on public release, for the investigation of accidents and as a tool to improve operational safety. 
  • ​R-15-022 Require rail transit agencies to implement transmission-based train control systems that prevent train collisions.   

To all Class I Railroads:  

  • R-25-09 Require all on-track RMMs with booms or other movable extensions, including leased or contracted RMMs, be equipped with a 360°people detection system that covers the length of the boom or extension in all directions and alerts operators when people are within an unsafe proximity. 
  • R-25-08 Require all on-track roadway maintenance machines (RMMs), including leased or contracted RMMs, to be equipped with collision avoidance systems that can detect people, objects, or other machines on the ground and automatically stop the RMM before a collision.  
  • R-23-04 Equip all trains with an autonomous monitoring system, such as vehicle/track interaction, to detect track geometry defects. 
  • R-13-026 Install in all controlling locomotive cabs and cab car operating compartments crash- and fire-protected inward- and outward-facing audio and image recorders. The devices should have a minimum 12-hour continuous recording capability.  

To the Association of American Railroads:   

  • ​R-20-31 Revise your Manual of Standards and Recommended Practices, Locomotive Electronics and Train Consist System Architecture, Standard S-9152.v2.2, Paragraph 3.8.8 to develop a communication protocol that will continue to transmit an emergency air brake command to the end-of-train device until a confirmation message or a decrease in brake pipe pressure message is received by the head-of-train device.  
  • R-24-019 Develop a database of bearing failures and replacements and make it available to railroads, regulators, and investigators to help determine and address failure risk factors. 

To the American Railway Engineering and Maintenance-of-Way Association: 

  • ​R-20-14 ​Develop a recommended practice for operator presence controls in self-propelled roadway maintenance machines to protect workers from unintended equipment movement.  ​ 

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