Wikipedia says "Originally, Caltrain employed Parsons Transportation to develop a custom PTC system, called CBOSS, for CalMod, but due to delays, Caltrain switched to Wabtec and their I-ETMS system."
Everything to do with California rail expansions seems to end in fiasco, largely due to repeated attempts to reinvent the wheel. From what little we've seen so far, it looks like DB and Alstom are playing it safe by proposing proven equipment and technologies, which should save us headaches in the future, as long as Transport Canada doesn't force them to adapt systems to meet the arbitrary differences between TC regulations and EU regulations.
My biggest question is whether Alstom will propose ETCS Level 2 or Level 3. Level 2 has been in service for decades on many lines across Europe, but it doesn't support moving blocks. Level 3 can theoretically provide up to 30 tph on a single track, but it's less proven - when I wrote that assignment there weren't any systems fully in operation yet. There are also challenges related to its purely communication-based nature, primarily related to other trains which need to share the tracks.
In its purest form, ETCS L3 doesn't require any wayside detection equipment (e.g. axle counters, track circuits), which in theory makes it cheaper to maintain than L2 or L1. But in order to achieve that, all trains on the line need to have train integrity monitors. That means that the train itself needs to confirm that the train is still in one piece, and a coupler didn't break, leaving a car sitting on the line behind. This is fairly straightforward for passenger trains, but would be a large ask for freight operators given that freight cars roam around the continent, and therefore virtually all cars on the continent would need to be retrofitted. Although CN no longer owns the core rail network in Toronto, they do still have trackage rights, and do therefore have some influence on the decisions related to signal systems.
To overcome these limitations, ProRail (Dutch railway operator) has proposed to use an
ETCS Hybrid L3 system where instead of moving blocks, they would use micro blocks. Each physical block would be divided into many virtual blocks, which would be used by (passenger) trains equipped with integrity monitoring. The (freight) trains which lack monitoring would only have access to the larger physical blocks, using the wayside integrity monitors. Given that moving blocks would only get updated every 10 seconds or so anyway, this provides nearly the same capacity for passenger trains as a moving-block L3 system, while reducing equipment requirements for freight operators. The fact that the micro-blocks match up with the physical blocks makes it much easier to overlay the physical and virtual movement authorities than with a system which combines moving blocks for passenger trains with fixed blocks for freight trains.
To cut on maintenance costs, ProRail also suggests that the physical block sizes could be increased compared to today, since the freight trains can be scheduled during times when line capacity is not critical. Doubling the physical block size cuts the amount of detection equipment in half.
