According to the UITP World Metro Figures 2021 report, approximately 3,300 km of new rail infrastructure was put in service between the start of 2018 and the end of 2020. This represents an infrastructure growth of 25% globally. During this timeframe, operational fleets worldwide increased by 28,000 vehicles to a total of 140,000 vehicles. In 2019, an average of 190 million passengers per day were taking the metro globally. This is an increase of 20% compared to five years ago. Rail operators are constantly striving to keep their trains moving safely, providing superior and reliable services to the riders, and lowering their operational cost.

Legacy fixed block signaling systems—a system that uses signals to prevent a train from entering an occupied fixed section of track—can no longer meet the increasing demands. A modern railway signaling system called “Communications-based train control (CBTC)” was introduced in the mid 1980s with the objective to achieve maximum capacity while maintaining the safety requirements. CBTC is mainly used in urban railway lines and automated people movers (APM), although it can be deployed on commuter lines.

What is CBTC?

As defined in IEEE Std 1474.1, “CBTC system is a continuous, automatic train control system utilizing high-resolution train location determination, independent of track circuits; continuous, high-capacity, bidirectional train-to-wayside data communications; and train-borne and wayside processors capable of implementing automatic train protection (ATP) functions, as well as optional automatic train operation (ATO) and automatic train supervision (ATS) functions.”

Key Benefits of CBTC

Here are some key benefits that CBTC brings to the rail operators:

  • Improved safety: With implementation of CBTC, the location of the train can be determined with a high degree of accuracy, independent of track circuits. The speed of a train can be regulated to protect trains against collision, excessive speed, and maintain the safe braking distance and train separation. With additional functions such as programmed stopping, door control, route interlocking, work zone protection, and highway grade-crossing warning, accidents and hazardous conditions can be significantly reduced.
  • Maximize capacity: The key objective of deploying CBTC is to allow rail operators to better utilize their railway infrastructure, maximize the capacity by keeping the headway between operating trains at minimum while maintaining the safety requirements.
  • Enhanced passenger experience: CBTC enables trains to run closer together at higher speed, meaning faster services to the riders. With increased precision of train location information, the accuracy of real-time arrival information can be improved significantly. And thanks to CBTC, riders can enjoy smoother rides because acceleration and braking are controlled by the system so passengers can expect more consistency in terms of train operation.
  • Reduced CapEx and OpEx: As CBTC technology evolves, the system becomes more compact, and architecture is getting simpler. This means less equipment at wayside that is easier to implement and maintain. Moreover, these systems allow rail operators to monitor trains and adjust the performance level of individual trains to maintain schedule. The CBTC system provides flexibility to the rail operators to respond to schedule changes and emergencies more efficiently.
  • Improved sustainability: CBTC enables different levels of Grades of Automation (GoA) and has proven to be more energy efficient than traditional manual operation. With automatic speed regulation provided by the system, unnecessary acceleration and braking are not required, which leads to big energy saving. With reduced power consumption and less air pollution, environmental sustainability is improved.

Key networking challenges to consider

Although CBTC brings tremendous benefits to the rail operator, there are some key networking challenges the rail operator needs to consider when deploying this solution:

  • Ultra-reliable train-to-wayside wireless communication: Successful operation relies on reliable bi-directional train-to-wayside wireless communication when trains operate at high speed. Mission critical systems like CBTC should be designed to achieve network latency less than 500 msec, wireless handover time of less than 50 msec, and less than 0.1 percent packet loss. Other physical parameters that cause poor wireless connectivity need to be carefully studied. These include lack of line of sight, electromagnetic interference, channel interference, spectrum congestion, and limitation of physical environment for radio and antenna installation. Cisco Ultra-Reliable Wireless Backhaul radios and Cisco Catalyst IW9167 Series outdoor access points are designed to provide reliable wireless connectivity for any application, anywhere.
  • Resilient and high available onboard and trackside infrastructure: The CBTC system is composed of five major sub-systems in general: train-to-wayside communication system, CBTC onboard equipment, wayside equipment, backbone network, and control center. Depending on the supplier, the architecture can be either centralized or distributed. Due to the criticality of the system, network redundancy and high availability must be taken into consideration during the system design phase, and good tools are required for network management, automation, provisioning, service assurance, policy, and security implementation. Check out Cisco Connected Communities Infrastructure (CCI) Solution Design Guide for details about designing wayside infrastructure for rail operation.
  • Cybersecurity: Digitization of rail operation requires strong cybersecurity. Attacks on vital rail systems can cause train stoppages, unsatisfactory rider experiences, and could potentially even cost lives when trains derail or collide. Experience has shown that a strategy of trying to simply “air-gap” and isolate operational networks does not prevent attacks. A comprehensive, systematic, and coordinated approach is needed. Challenges such as the following need to be considered: only authorized users and devices are connecting to the network, users and systems can access only data and services for which they are authorized, users are not connecting to malicious sites, malware is not brought into systems, and only legitimate traffic is transiting the network. Robust tools are needed to manage profiles and policies at scale and monitor those users and devices on the network to ensure compliance with those policies. All of this must be done in a way that enables a quick response to new threats and intrusions as they emerge.

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Wei Zou

Solution Architect

IoT Product Management Networking