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Tuesday, December 6, 2011

Speed Signaling with Caltrain

Between 2002 and 2004 the Caltrain commuter route on the peninsula between San Francisco and San Jose underwent a near total rebuild to bring it up to the same high tech standards as many of the companies that had their headquarters adjacent to its tracks. At the turn of the 21st century the line was operating much as it would have been at the turn of the 20th with basic single-direction Automatic Block Signal operation with hand operated crossovers at temporary block stations where orders would have hooped up to trains during single line working. Much of the line still used jointed rail and there were only five interlockings on the entire route clustered at the north end near San Francisco, one of which was the 4th and King St terminal and the three of the remainder being used by freight trains accessing spur tracks.

Fortunately for history the line was documented by a West Coast signal fan and you can see his work here.

Two years later the line could not be more different. It was upgraded to fully bi-directional CTC operation with welded rail and large sections with concrete ties. Stations were rebuilt and two long 4-track passing sections were constructed near the Northern and Southern portions of the line to allow new express train services to pass locals without delay. A plethora of new interlockings were installed to allow 2-track express passing or just easy recovery from engineering works. Again, all of these changes were documented by the same signal fan.

What is perhaps more interesting is that as Caltrain owned the tracks between CP-COAST and San Francisco it was free to make the decision to abandon the old Southern Pacific inherited 'route' signal rules and adopt more modern speed signal rules comparable to those seen in the east. As Amtrak had the long term contract to run the Caltrain services this better fit its operating practices elsewhere in the country.

The old route style signaling had been popular back when interlockings were few and far between and traffic densities light, but with increased routes and higher speed differentials Caltrain dumped the whole route concept and adopted a speed signaling scheme influenced by prior art, but with its own unique flavour.

The Caltrain signal rules can be found its the following rulebook documents. Also included are the Union Pacific route signaling rules still in service on the UP owned portions of track so you can compare and contrast.

Caltrain ETT No 2
Caltrain ETT No 2 Supplement No 4

So what is interesting is that Caltrain started with the typical "Northeast" style signal set with Y/Y as Approach Slow and *Y* as Advance Approach, but dumped the use of "bottom yellow" in Restricting signals, using *R* instead. With bottom yellows now free R/Y and R/R/Y could be tasked to Medium and Slow Approach. The system retains some Western influences with the Approach Restricting aspect and Caltrain also added some innovative new aspects such as R/*Y* as Limited Advance Approach, R/R/*Y* as Slow Advance Approach and R/Y/*R* as Medium Approach Restricting. They also logically extended the Northeast style system by using R/Y/Y as Medium Approach Slow.

Because no automatic signal aspect requires 3 heads (a problem caused by using Y/R/G for Approach Slow) Caltrain was able to adopt a uniform visual aesthetic for its signals (probably to the delight of its vendor, US&S) by fitting all standard block signals with 1 head, distant signals with 2 heads and interlocking signals with 3 heads. Each head in turn was fitted with all three lamps, if they were needed or not. This gives the engineer an easy way of identifying what sort of signal they are facing, even if it means Caltrain spent a lot more outfitting signal lamps that would never need to be illuminated. On some of the 4+ track home signal gantries this can lead to quite the interesting Christmas Tree effect, especially when flashing aspects are involved.

This brings us to our main feature. Back in March I was out in the Bay Area for a conference and I was able to capture video from the north-facing railfan window of a gallery car of the entire line. Now this consists of about 40 minutes worth of video showing nothing but Clear signals and is probably something you don't really need to see, however I later filmed a second partial run at night where my express train takes the Bayshore passing route for some reason which shows off some aspects other than Clear. Also in evidence are the numerous grade crossings (including pedestrian grade crossings at stations which the trains have to whistle for) and this really cool Southern Pacific era 8-track signal gantry that was fitted with new signals and left in place. In that same area you can also see the last hand operated crossovers on the line used by local freight trains to switch between goods sidings that straddle the main line.

The first video between Millbrae and Bayshore can be seen here:

There is a gap between the way caused by my camera batteries running out.

In the second video you can see the new Lunar White marker lights that were attached to the signals in the terminal area for some reason. The terminal is the only un-resignaled portion of the line retaining its original Southern Pacific searchlights and pneumatic point machines (possibly the only pneumatic points west of Kansas City) and the Lunar Markers may be to differentiate the special case terminal signals with the new speed signaling system.

Anyway, I hope you all enjoy the video and see that converting to Speed Signaling is an achievable goal.

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