I’m investigating CBOSS, Caltrain’s abandoned homespun Positive Train Control system, hoping to gain insight into what the system would have looked like on the technical level, and how it would have compared to existing (and now widely deployed) options like ITCS, I-ETMS, ACSES, etc.

Huh?

A little more than a year ago, Caltrain finally launched electric service between San Francisco and San Jose after decades of planning, construction, and procurement. The project has been incredibly successful, dramatically increasing ridership, cutting travel times, and preparing for California High Speed Rail to enter San Francisco (a project which, despite the claims of detractors, is happening). Though parts of the process were painful, for riders and for Caltrain, the prevailing sentiment has been that it was all worth it. In the year and change since, little attention has been paid to what I think is the most interesting part of the project: Caltrain’s aborted attempt at a custom PTC system.

On February 11th, I submitted a public records request to the Peninsula Joint Powers Board (JPBX, PCJPB, or Caltrain) under the California Public Records Act, seeking information related to the architecture, design, and technical workings of the doomed Advanced Signal System Project, or CBOSS, which was an attempt to create its own FRA complaint PTC system.

Others have written many words about CBOSS.¹ Much has already been covered. I seek only to look in to the technical nature of the project. Very little is publicly known about how CBOSS would have worked, how it would have interfaced with California High Speed Rail’s own PTC and signal systems, and what it would have looked like in operation.

Timeline

1. I refiled records request via NextRequest portal after request by email was ignored - 2/11/26
2. PCJPB confirmed receipt of request - 2/23/26
3. I followed up on request status - 3/8/26
4. PCJPB updated me, saying that staff are reviewing request and gathering records - 3/9/26
5. I inquired again about request status - 4/1/26 ← We are here

If you want me to ping you when I update this post, email blog+cboss@xferok.com :).