High Speed Rail Signaling Question

With all of the high speed rail projects popping up all over the US, it makes me wonder if there will be a new standard for signals. Does anyone know if new signals will be or are emerging as we begin to revitalize our passenger rail system?

Vince

Moderator's Note: changed thread title, 3/3/13

Welcome, Vince!

Most high-speed systems are already using a cab signal system, which broadcasts the signals directly to trains through a pulsed electrical signal transmitted through the rails. Some of those systems have few to no wayside (standard fixed) signals at all. The most advanced systems are Automatic Train Control systems that prevent high-speed collisions and automatically stop trains when there is a track obstruction. Just over the horizon, there are GPS-based Positive Train Control systems that theoretically require no operators, except for safety overrides.

Is there a particular innovation you are interested in learning more about?

Perhaps an "ERTMS style convergence" directed by FRA as ERA is doing in Europe is what was in mind of the OP?

vinced wrote:With all of the high speed rail projects popping up all over the US, it makes me wonder if there will be a new standard for signals.

I wasn't aware there was an old standard. AFAIK, each railroad has its own way of signalling, and sometimes different divisions on the same railroad use different signals.

vinced wrote:Does anyone know if new signals will be or are emerging as we begin to revitalize our passenger rail system?

I'd put the question a different way: what sort of signalling is envisioned for those high-speed rail corridors that are far enough along in planning to have considered the question?

For that matter, how does the signalling on the one more or less high-speed rail corridor the US has (NEC) differ from what your average freight railroad has?

Are there signalling systems (existing or proposed) that can work well for both high-speed traffic and for low-speed, high-density traffic, such as commuter railroads or freight?

amm in ny wrote:For that matter, how does the signalling on the one more or less high-speed rail corridor the US has (NEC) differ from what your average freight railroad has?

IINM, the "average freight railroad" (top speed 79 mph for passenger trains) has CTC signals as its top level, and Class 4 track. The Northeast Corridor on its fastest segments would be CTC, cab signals/ACSES and Class 8 track, and it takes quite a chunk of change to maintain that (seemingly arbitrary) standard. The 79-mph top speed for passenger trains railroads without cab signals and/or positive train stop type signaling dates back to the ICC's reaction to the 1946 train wreck in Naperville IL.

amtrakowitz wrote:

amm in ny wrote:For that matter, how does the signalling on the one more or less high-speed rail corridor the US has (NEC) differ from what your average freight railroad has?

IINM, the "average freight railroad" (top speed 79 mph for passenger trains) has CTC signals as its top level, and Class 4 track. The Northeast Corridor on its fastest segments would be CTC, cab signals/ACSES and Class 8 track,

What I was intending with my question was to ask how the signalling model/algorithm differs. E.g., different block lengths (or something other than block signalling), different or additional aspects, additional considerations when setting signals, etc.

AFAIK, the track quality is not part of the signalling system (though obviously 10 mph track doesn't require fancy signals), and cab signals and ACSES simply reproduce and enforce the signals, rather than affecting what signal aspects apply.

What inspired my question was a claim elsewhere that running HSR on commuter tracks would require a signalling system that would not work as well for the commuter rail service as what was already there. It sounded like they were saying that you could make a signalling system that would work for HSR, or one that could handle low-speed, high-density traffic, but not one system that could handle either one.

Without searching for that thread, I would assume it would have to do with the longer stopping distance needed by a HS train vs. a commuter train, which raises the question of why anyone would want to mix the two on the same tracks in the first place. If the HS train is only using the commuter tracks to gain access to a centrally located station (would California HS access to San Francisco over Caltrain be an example?) the HS trains would surely be restricted to something like present speeds, in which the signaling for commuter trains would be appropriate. This is the practice in France and Germany when HS trains use the "classic" network, which they do in order to reach a lot of places which would never justify the construction of HS routes.

ExCon90 wrote:Without searching for that thread, I would assume it would have to do with the longer stopping distance needed by a HS train vs. a commuter train, which raises the question of why anyone would want to mix the two on the same tracks in the first place.

It does sound impractical, but in the USA, we do have an example where the same line has both commuter trains and trains that are the closest thing the USA has to "high-speed": AMTRAK's NEC between Philadelphia and NYC.

The question isn't whether you'd want to mix high-speed and low-speed trains on the same track at the same time, but rather whether you'd want to sometimes use a particular track for high-speed trains and for low-speed trains at another time. After all, a track can only run trains in one direction at a time, but even on lines where a given track runs in one direction most of the time, the tracks are usually signalled for traffic in either direction.

I think this is likely to be a common situation for HSR in the USA. Acquiring completely separate rights-of-way is expensive, prohibitively so in metropolitan areas, and "metropolitan areas" tend to cover a lot of land due to sprawl, so I think that large chunks of any HSR route are likely to be existing routes, upgraded for higher speed and with an extra track where necessary.

What's running on the NEC now doesn't really fall under the heading of High Speed Rail. If money is going to be spent on a line capable of true HSR, I can't see wasting all those slots on a commuter train; there would have to be a hell of a long gap after a local before the next HS train could leave.

ExCon90 wrote:What's running on the NEC now doesn't really fall under the heading of High Speed Rail. If money is going to be spent on a line capable of true HSR, I can't see wasting all those slots on a commuter train; there would have to be a hell of a long gap after a local before the next HS train could leave.

Is "true HSR" anything like a "True Scotsman"?

(Obligatory foamer pin-up picture

However, I'm not interested in (IMHO pointless) arguments over definitions of HSR. I am only interested in the signalling question (the title of this thread) The NEC is an example of a line (not track) where 90+ average mph trains mix with 30-40 average mph trains, and the signalling system there clearly has to deal with that.

Does anyone here know what the NEC's signalling system does to handle the mix of speeds?

I don't know the technical details, but Amtrak signal engineers came up with a way of installing the capability to maintain required spacing between trains at speeds up to 150 mph by superimposing additional codes on the existing track circuits while at the same time allowing commuter trains not so equipped to continue operating with just 4 cab-signal indications just as they have all along. The wayside signals in this territory provide for a flashing vertical-green aspect called "cab proceed" (I think), meaning be governed by cab-signal indication. A question for an engineer: if a westbound NJT Midtown Direct is approaching SWIFT to take the 80-mph diverging route to the M&E, what appears on the waysides and on the cab signal?

BTW, thanks for the photo of the Flying Scotsman; I saw it on its visit to this country -- what -- 40 years ago? -- operating on the NEC.

ExCon90 wrote:I don't know the technical details, but Amtrak signal engineers came up with a way of installing the capability to maintain required spacing between trains at speeds up to 150 mph by superimposing additional codes on the existing track circuits while at the same time allowing commuter trains not so equipped to continue operating with just 4 cab-signal indications just as they have all along.

I'm a bit rusty on this stuff myself but you've hit it on the head, as far as I remember. There are actually two code generators per circuit, and the high speed trainsets can "listen" for both sets of codes. Whereas traditional NEC cab signaling is based on the codes 0 (no code), 75, 120, and 180, the new overlay codes allow things like 75/75 and 180/180 (which is the so-called "Super Clear" aspect for HSR).

Glad to have that confirmation -- I was wondering what the additional codes were.

ExCon90 wrote: A question for an engineer: if a westbound NJT Midtown Direct is approaching SWIFT to take the 80-mph diverging route to the M&E, what appears on the waysides and on the cab signal?

If it is anything like the eastern portion of the NEC, which I assume is yes, there would be a cab speed aspect, allowing the commuter train to take the switch at 80 mph. We have the same situation here in Attleboro, MA at HOLDEN interlocking where our MBTA trains make the diverging move, Trk 1 to Trk 3 West at 80 mph, operate on a Cab Speed aspect....also, the distant signal displays a Cab Speed Aspect

What is the highest cab speed indication that a commuter train can read? In other words, if for any reason a commuter train were scheduled to skip Attleboro and go straight through on 1, would he still only get a cab speed 80? Or would he get a MAS indication?