Let's talk about signal problems...

[pm9]

Hi everyone,

I'm new to Railroad.net but becoming more and more interested in subway operations every day. I live in Cambridge, and naturally I hear quite a bit about signal problems on the MBTA Red Line...what are these, exactly? Is it a hardware malfunction? Software? Do they require physical attention to fix? And why are they so frequent? Where can I read more?? Thanks!

[Disney Guy]

The Red Line uses wireless control where transmitters along the line send information to passing trains that adjust their speed automatically. The line is divided into different speed zones, say, 10 MPH, 25 MPH, etc., defined in advance by settings in various control boxes and sensor boxes and/or software in a central control station. Additional speed restrictions and stop locations are dynamically added and deleted to keep trains from getting close to each other, mimicking the block signal system standard on railways. Much of the time the operator can leave the controller in "maximum" speed and the train will drive itself.

In a few locations there are regular "traffic light" signals where the train must be operated manually but there is still a maximum speed enforced by the wireless mechanism. Also the operator must pro-actively stop at stations for platform and passenger safety and to achieve a smooth stop.

Problems occur when the sensors (such as to detect a train close up ahead) malfunction, or erroneously detect a switch as being changed for special operations necessitating operator or even flagperson control of approaching trains. Where sensor problems occur the affected track zone becomes a manual control zone and and the operator is usually restricted to 10 MPH.

Colored lights and a buzzer in the cab will alert the operator to the need to assume manual control and the train will (should) stop if the operator does not take action quickly enough.

[pm9]

quite interesting! To someone who doesn't know very much, that almost seems futuristic; or at least relatively modern. How many systems nationwide are automatic?

Also, do the 01500-01700 cars adjust their speed automatically as well, or is that only the 01800 series? What kind of retrofitting do they have to do in order to have pre-1980s equipment be connected to this stuff? I was recently noticing with the 01800s (and only them) a sort of slowdown-speedup-slowdown cycle (exactly 3 times) right after the Harvard curve on the way to Central. It stopped a few days ago, but got me wondering anyway...

[MBTA3247]

It's not a fully-automated system: the operator still has to keep their hand on the controller, and is free to adjust the speed to whatever they like (or stop altogether) as long as they don't exceed the maximum speed for the block they're in.

Currently there are no fully-automated systems in the US. The Washington, DC metro used to be (with an operator on board to control the doors at stations) but that was discontinued after the wreck in 2009.

A lot of the signal problems on the T are due to the system being decades old at this point and overdue for a complete replacement.

[Disney Guy]

I think that the Washington DC and BART San Francisco subway trains could drive themselves from the day the lines opened, or if not, within a few years after the lines opened. Then, the public was not ready for driverless trains so a driver sat in the cab anyway. There was at least one publicized instance where the operator got out of a BART train to inspect something and the train closed its doors and took off, doing a pretty good job of driving itself for several stations until another operator intercepted it and took control.

Even with no automation, the controller already accelerates the train smoothly and the maximum speed depends on what notch the controller was put in together with voltage and whether the train was going uphill, downhill, etc. The automatic control, in some cases, retrofitted, needs to monitor the speed, cut the power, coast, apply the brakes, and then apply power again as needed, If the controller was set in a low notch, the automation will still work although the maximum speed at any time could be less than the speed limit for the track section. If the controller was still in a high notch when the automation applied power or if the operator set the controller immediately into a high notch, the train will still accelerate smoothly from a dead stop. The Boston trains do not have the mechanism to open the doors, wait a predetermined time, close the doors, and (after all doors close fully) start up from a station.

(As mentioned earlier, the Boston trains require that the operator have the controller handle under his control for the train to move at all, automated section of track or not.)

[MattW]

MARTA in Atlanta is pretty close to fully automated. They still have an operator open and close the doors, but they can just press a proceed button and go along for the ride. It's usually a much rougher ride though as the system blasts full throttle until it "overspeeds" then it kicks in full braking which usually drops the speed by 7mph, then back to full throttle etc.

[ExCon90]

PATCO (Philadelphia--Lindenwold) is similar. The only non-automated function is the operator closing the doors when passengers have boarded; he doesn't need to do anything else until it's time to leave the next station. In the original design of the cars he isn't even in an enclosed cab--he sits inside an enclosure about the height of a bank partition so passengers can see that there's actually somebody there. (He sits on the left--on the right side there used to be an ideal railfan seat with a splendid forward view.)