Positive train control

Positive train control is a technology designed to avoid train to train collisions and derailments caused by speeding. Implementation of PTC by commuter and large freight railroads has been mandated by Congress after the 2008 crash between a Metrolink train and a freight train in Southern California. The deadline for compliance was originally set for 2015 but has been extended to the end of 2018.

The PTC system uses computers, GPS, and data radios to detect train location and enforces track speed and signal rules. If the engineer runs the train past a red signal, the train will automatically stop. If the train is running faster than the speed limit, whether because there’s a train or a curve ahead, the train will also automatically stop. PTC would generally act as an overlay (not a replacement) of the railroad’s signal system. Engineers would still maintain full control of the train unless a rule has been violated. PTC however would not prevent collisions with automobiles or trespassers because their movements are more sudden and cannot be easily detected.


Before the 2008 crash, Caltrain has advocated some form of communication based signal system to enhance capacity and permit the use of non-FRA compliant trains. The 2008 crash created the urgency which became a mandate.

Caltrain in 2011 awarded a contract to Parsons Transportation Group for a PTC system known as CBOSS. Among other infrastructure changes such as the installation of fiber optic lines on the corridor, the plan would implement a PTC system based on General Electric’s technology.

Due to project delays (largely caused by GE’s abandonment of its PTC product), Caltrain terminated the PTC contract with Parsons in February 2017. Caltrain intended to continue the development of the system using Parsons’ subcontractors. However in March 2018, Caltrain decided to abandon the CBOSS technology and awarded the PTC contract to Webtec, which has been developing an alternative PTC technology (I-ETMS) used by major railroads including Union Pacific.

Under the new contract, Webtec would reuse as much infrastructure as it can that has been delivered from the previous contract, and to complete the project so that Caltrain can enter to a demonstration phase as required by law.

Webtec was the second highest rated vendor when the company submitted an offer for the original PTC contract in 2010/2011. But Caltrain at the time determined that Webtec’s technology wasn’t as developed or desirable from the passenger railroad perspective. However over the years, implementation of Webtec’s technology by major freight railroads (and passenger railroads that run on their tracks) made Webtec more desirable. Implementation of Webtec’s technology by Caltrain also resolves a compatibility issue between Caltrain and Union Pacific. If Caltrain were to adopt a different PTC technology than UP, as it intended with do with CBOSS, Caltrain would have to install a separate Webtec system for trainsets that operate south of Tamien on Union Pacific tracks to comply with UP’s rules.