More than 800 audio-frequency track circuits are now in service across 26 stations on the Massachusetts Bay Transportation Authority's Red and Orange Lines, as Knorr-Bremse moves its Boston signalling modernisation into its final delivery phase.

The programme, launched in 2019 and valued in the lower triple-digit million-euro range, is scheduled for completion by the end of 2026. Knorr-Bremse is delivering it through its KB Signaling business, deploying the company's AFTC5 Audio Frequency Track Circuit platform across one of the busiest metropolitan networks in the United States.

The staged approach has allowed daily passenger services to run throughout the works. For MBTA, the project ranks among the most extensive signalling modernisation efforts in the network's history, and demonstrates that legacy infrastructure can be upgraded without wholesale replacement or prolonged service disruption.

"The modernization of Boston's Red and Orange Lines – covering 26 stations and now surpassing 800 AFTC5 track circuits in service – represents a major milestone and clearly shows how complex signaling projects can be delivered successfully, step by step, while keeping daily operations running," says Jeff Baker, Managing Director of KB Signaling. "We are proud to support MBTA as a trusted partner and, together with our local engineering teams, to help advance safer, more reliable, and more efficient rail operations – delivering proven performance even in highly complex urban transit networks."

Digital train detection

The AFTC5 system marks a shift from analogue trackside equipment to a fully digital generation of train detection. It transmits audio-frequency signals directly through the rails, supporting reliable train detection and the data-based exchange of safety-critical information, including train speed commands.

The outcome, according to the supplier, is precise train positioning, dependable track clearance and safe train separation — the operating foundation for higher-performance service on the two lines.

Those claims are consistent with the deployment record so far: the 800-plus circuits in service represent measured progress against a programme that has run for six years without taking the network out of operation. The 2026 completion date remains a projection, dependent on the final delivery stages still ahead.

Strategic weight for Knorr-Bremse

For Knorr-Bremse, the Boston contract is a reference project in a segment the group has identified as a growth driver. Dr. Nicolas Lange, Member of the Executive Board of Knorr Bremse AG with global responsibility for the Rail Division, frames signalling as central to the company's positioning.

"Around the world, rail networks are entering a new phase of digitalization and modernization – unlocking growth opportunities for advanced signaling and trackside technologies," says Lange. "For Knorr Bremse, signaling and electronics are a cornerstone of our strategic journey toward becoming a Tier 1 systems partner for the entire rail ecosystem. The technologies combine a strong, long term business model with a growing demand for high performance infrastructure solutions. Projects like Boston illustrate how our technologies translate vision into reality – and how we deliver complex programs with a clear focus on our customers."

Boston is not the only deployment. The AFTC5 platform is already in use on long-term signalling transformation programmes in Los Angeles and Chicago, where operators are applying the same incremental model: replacing ageing analogue trackside equipment with digital architectures while maintaining service availability.

That model carries weight for operators elsewhere. Rail authorities facing growing passenger demand and constrained funding are watching how safety-critical systems can be renewed line-section by line-section rather than through closure-led renewals. The MBTA programme shows a large US urban network doing exactly that, with the remaining work scheduled to close out by the end of 2026.