> From: "Peter D. Ehrlich" <norcalrr@sprynet.com>
> Date: Fri, 22 Jan 1999 08:02:47 -0800
>
> >(As many have pointed out, that's why not using the X-tracks at
> >Embarcadero is so stupid -- since it takes longer, it
> >_decreases_ the number of trips per vehicle.)
>
> In an emergency situation, the Embarcadero diamond is still used to
> turn back trains. This occurs when there is a blockage in one or
> both of the pocket tracks in the MMT. I hate to say this, but the
> onset of ATCS is that we don't have to use the slow, cumbersome
> Embarcadero crossover for regular service any more. This in itself
> is a big improvement.
>
>Peter, the problem with the crossover was the fact that it was unique
>and that it was a single point through which all trains on the entire
>system had to run. It was "slow" only because contention for paths
>across this single point caused tunnel-long backups.
>
>Two additional turnback locations in the MMT (and others at Folsom and
>Fifth/King) should have _added_ to this turnback point, adding
>additional flexibility. The original west-of-Embarcadero crossover is
>in fact vastly faster to use (single it involves no magic mystery
>tours of MMT) and no less "cumbersome" than the MMT turnbacks. For
>this reason it should be used by preference (when changing ends at the
>platform won't cause backups), rather than as a last resort.
>
>The baby has been thrown out with the bathwater.
>
>(And please, ATCS didn't buy use of MMT: it was Muni Capital Project's
>inexcusable and incompetent decision to make MMT depend on ATCS, not
>some inherent pre-existing signalling limitation.)
Unfortunately, Richard, you are completely wrong that using the Embarcadero
diamond is faster.
Such an arrangement works fine in heavy rail operations, such as New York's
Flushing Line, where trains are 11 cars long and scheduled on 90-second
headways. The reason it works there and not on Muni are many. First, the
Flushing Line is a dedicated right-of-way used by only one route. Second,
the motorman of the inbound train brings the train in and removes his air
handle and controller keys. Simultaneously, a fresh motorman gets in what
was the trailing cab and sets up for the outbound trip--all in less time
that it takes the train on the opposite platform to depart. As soon as the
train lines are charged and the train is ready to go, another train has
entered the station, regardless of whether that train has crossed over or
not, and the first train departs. All this is done with ordinary wayside
block signals and a manned tower, although the switches are set
automatically for the clear move, as were the Diamond switches BATCS
(before ATCS). BTW, my familiarity with how well the Flushing Line works in
moving trains in and out of a stub-end terminal dates back to 1954. This
efficient operation was most impressive to an eight-year-old kid, and was
the benchmark by which all future stub-end terminal operations were
measured.
Now I will tell you why Embarcadero Diamond doesn't work, even though,
theoretically, you feel it could. First, our trains do not have cars with
end doors. Each car is brought inbound with one motorman. Back when Muni
Metro began, we did have a fallback system of operators at Embarcadero
where a fresh motorman relieved an inbound train. This was the only time
in the history of Muni Metro where we came close to running a 90-second
headway in and out. This period lasted from 1980 to 1983 or 1984, when the
fallback location was changed to Montgomery--a much inferior arrangement.
Second, we do not have one dedicated route. Instead, we have five routes.
With trains of 3 or 4 cars, trains had multiple outbound destinations.
Combining of trains then, as now, counted on pinpoint timing of arrivals at
portals--which was almost an impossibility--and the hope that the train
were successful. Anyway, without a fallback system, each motorman has to
change ends. And then there is the "702" situation, which holds things up.
A fallback system would speed things up. But then you have the problem of
assigning a motorman to every car of the train, instead of just one
motorman, which can be done on a heavy rail system.
The Embarcadero Diamond arrangement was dictated by the arrangement of the
BART tunnels. Back in the 1960s, when it became apparent that Muni and the
City didn't know what configuration of inner terminal they wanted for its
subway system, they were forced to accept the BART-built design and we've
been stuck with the Embarcadero system ever since.
In a future signup, the M-Oceanview is going to Proof-of-Payment, with
2-car trains and one operator. Now, changing cabs at Caltrain is easy.
All the doors open, the train is in Cab/Street operation, and the motorman
has anywhere from 5 to 17 minutes to depart. Changing cabs in a 2-car
train in the MMT will not be that easy, and, in fact, may be impossible.
Trains will be in auto mode entering MMT, which precludes opening a side
door even when changing cabs. Once the motorman opens the door in a
location other than at the designated platform stop, ATCS is lost. The
only solution to this dilemma is for Muni to provide a fallback arrangement
back to Embarcadero to handle this line. Back to Square One!
Now, then, Richard. I ask you how *you* would make this situation work.
Peter Ehrlich