PCC Speed

[Fred Schneider]

I once raised the question of speed with an electrical engineer at GE
... back in the late 1970s when I was working on the PCC books.

The 42 miles per hour balancing speed was calculated in 1936 based on GE
1198A1 or Westhouse 1432 motors, both internally ventilated, and a
36,000 pound car on level, tangent track, with 550 volts.  I do not
remember if it also included a seated load, which would add another 8000
pounds.  Transit Resarch Corporation once printed (and I have no idea
where I put it) a graph showing balancing speed in relation to gradient
... it is somewhere in the tons of paper at home.  I think the balancing
speed was down around 15 miles per hour on a 10 percent grade, maybe 12
miles per hour on the steepest part of the Fineview line.  Therefore
your guess of 28 miles per hour up the 6% grade through South Hills
Tunnel is probably close.

The balancing speed (that at which the counter EMF generated in the
motor matches the voltage imposed on the motor) would of course vary
with gradient, load, curve friction, and voltage.

The 1936 car would accelerate at peak rate of 4.75 miles per hour per
second until in reached approximately 15 miles per hour ... enough to
get through the intersection ahead of a Chevy with a flathead six.
Above 15 miles per hour, the acceleration curve began to taper.  It was
quite normal to get to 25 miles per hour within one city block.   The
car simply was not designed to run full bore ... it was designed to
"float" in traffic which customarily moved at 25 to 30 miles per hour.
It had very brisk acceleration at lower speeds.

How long did it take to get to 42 miles per hour?  Over 30 miles per
hour, the acceleration curve was virtually flat. And the faster the car
went, the weaker acceleration became.  A PCC would accelerate to 30
miles per hour in about a city block (normally considered about 0.1
mile) but it took almost a full mile to get up to 42 miles per hour. 

So the chap who told me he chased one across Philly's Chestnut Street
bridge at 55 probably caught up to the car!  My memories of going like
hell over the 6th Street Bridge in Pittsburgh were probably affected by
the sound of the bridge itself drumming ... when I go back and drive
over the bridge today, and realize the gradient approaching it and the
braking time needed to stop at Fort Duquesne Way at the other end, I
suspect top speed wasn't anywhere near 40 ... 20 might be more like it.
And those 60 or 70 mile per hour rides in the New York subways?  The
fastest express trains ran somewhere near 45 miles per hour!

Shaker Heights cars had 1 inch larger wheels ... balancing speed might
have been about 44 miles per hour and maybe they got to 50 inbound from
Shaker Square with a swinging load in the morning rush. But it was
probably more like 30 coming out in the evening.  

There are some long downhill stretches on Boston's Riverside line ...
maybe something over 42 was also possible.

You must also note that, like reptilian evolution, the PCC got heavier
over time.  The original Brooklyn cars weighed around 35,900 pounds.
Top weights reached 11 percent more than the original figure, which
would also lower the balancing speed.  And how about the weight of paint
(this didn't apply to Pittsburgh) but Philly cars probably grew much
heavier over time simply by adding pigments.  The use of blown motors
after 1940 may have slightly raised the speed and compensated for the
heavier cars.    

But for the most part, the fish gets longer with each narration.  

-----Original Message-----
From: Jim Holland [mailto:pghpcc at pacbell.net]
Sent: Thursday, November 04, 1999 8:54 AM
To: pittsburgh-railways at dementia.org
Subject: PCC Speed