Subway Surface- top speeds and cab signals

Wdobner wrote:I can't speak for SEPTA's operations exactly, but I'm fairly certain that in NYC, Chicago, and other places I believe that speed enforcement on curves and such was done with a signal timer. The timer was set so that it would clear only when it took an amount of time greater than the time needed to travel the length of track at a set speed. If the timer was set for 25mph or 36.667 ft/s and the timer section was 200 feet long then you'd better spend more than 5.45 seconds in the section or your tripcock would be triggered and the train would go BIE. I've heard some stories from folks who drove trains in the B.S (Before Speedometer) period and it sounds like during the first week or so of operation on a line you pretty much played it safe and ran slow or just accepted the BIEs and tried to go fast. Over time the operators would learn how to gauge their speed at the various timers and likely over other parts of the route without speed enforcement.

I thought the PCCs couldn't go into the tunnel. Clearance & signal issues.

I apologize for the thirdhand information, but I believe I heard yesterday on a railfan trip that one of the participants had been told by a SEPTA higher-up in the Engineering dept that there is no physical reason the PCC IIs cannot run in the tunnel. Of course the lack of CBTC compatibility makes their operation in the tunnel a very temporary proposition, and I'm not even quite sure why anyone would want them there. I suppose SEPTA is concerned that if people get word that the PCC IIs can be operated in the Subway Surface then there will be calls from disabled passengers for them to be operated at least on the Route 10. They may not have enough PCC IIs to operate both the 15 and some 10 runs during peak hours, but off-peak a few likely could be spared. With the cumbersome wheelchair lifts accomodating a wheelchair passenger in the Subway Surface potentially could delay several trolleys.

Both of your observations are correct about SEPTA. First, the signal system was intended to maintain a certain speed around curves and entering stations. The same was true for the Market-Frankford system as well. There are many "timed" signals in the Subway/Surface tunnel and there were many on the Blue Line side as well.

There really is no "physical" reason why the PCC-II's cannot enter the tunnel. The only reason is the non-compatibility of the PCC's with the CBTC system.

And, as I was told by an Elmwood operator, the PCC-II's were restricted from the tunnel due to a lack of roof-mounted headlight to illuminate the overhead in the tunnel.

As for the lack of CBTC/cab signal equipment on the PCC-II's, why couldn't they just run visually in the tunnel on a limited basis (fan trips, for example)? Just use caution on curves, and wouldn't any following LRV's get reduced speed indications on their cab signal displays?

Or does CBTC rely on the position of the LRV ahead to determine a safe cab signal indication?

Silverliner II wrote:And, as I was told by an Elmwood operator, the PCC-II's were restricted from the tunnel due to a lack of roof-mounted headlight to illuminate the overhead in the tunnel.

As for the lack of CBTC/cab signal equipment on the PCC-II's, why couldn't they just run visually in the tunnel on a limited basis (fan trips, for example)? Just use caution on curves, and wouldn't any following LRV's get reduced speed indications on their cab signal displays?

Or does CBTC rely on the position of the LRV ahead to determine a safe cab signal indication?

CBTC requires a transponder on every vehicle. Basically, it is operating the cars/trains, so it needs to know the position of every vehicle within a very small tolerance in order to be able to issue the appropriate speed commands.

So, the upshot is that you would simply not be able to safely run a non-equipped vehicle into the hole, without arranging for some kind of manual block enforced by a pair of block operators or some type of manually-controlled visible fixed signal. A fan trip, with no LRVs operating, would be possible, but would have to be done during a time when the LRVs are not in regular service.

jb9152 wrote:CBTC requires a transponder on every vehicle. Basically, it is operating the cars/trains, so it needs to know the position of every vehicle within a very small tolerance in order to be able to issue the appropriate speed commands.

So, the upshot is that you would simply not be able to safely run a non-equipped vehicle into the hole, without arranging for some kind of manual block enforced by a pair of block operators or some type of manually-controlled visible fixed signal. A fan trip, with no LRVs operating, would be possible, but would have to be done during a time when the LRVs are not in regular service.

And THAT answers my one big question on how CBTC (and moving blocks) work. I should have guessed that was the situation. And it answers my question on how the L line of the NYC subway will operate when they have full CBTC in place on that line.

Thanks.