From: whheydt@pbhya.PacBell.COM (Wilson Heydt)
Subject: Re: Alliance for a Paving Moratorium (Alert)
Reply-To: whheydt@PacBell.COM (Wilson Heydt)
Organization: Pacific * Bell, San Ramon, CA
Date: Tue, 5 Jan 1993 00:47:07 GMT

In article <1993Jan4.194523.20123@ntmtv> adrian@ntmtv.UUCP (Adrian Brandt) writes:
>In article <1992Dec30.164607.5327@pbhya.PacBell.COM>, whheydt@pbhya.PacBell.COM (Wilson Heydt) writes:
>|> In article <1992Dec30.002600.12884@pbhye.PacBell.COM> mjvande@PacBell.COM (Mike Vandeman) writes:
>|> >>Actually, a light rail line can carry the equivalent of a freeway, I 
>|> >>am told. They can reach 55 MPH or more.
>|> >
>|> >Actually, I believe that a heavy rail line can carry far more than any 
>|> >freeway full of SOVs, so is in a class by itself.
>|> 
>|> I wouldn't be *too* sure about that....  LA (for instance) has some pretty
>|> wide freeways...
>
>Time for some BOTECs (Back Of The Envelope Calculations).
>
>At best, a freeway lane can handle 1,800 cars per hour, an average of a
>car every 2 seconds.  Using a typical 1.1 people per car average, that
>gives a lane a people throughput of 1,980 (which I'll call 2,000 just to
>be generous).
>
>Now, a railroad track and its associated signalling typically allow for
>a maximum of a train every 2 to 5 minutes, depending on the system.  For
>CalTrain, a locally well-known heavy rail system, I'll use the 5 minute
>figure with 8 car trains.  Each car has seating for 148 people.  So an
>8 car train seats 1,184 people.  Trains every 5 minutes means 12 trains
>per hour which means seating for 14,208 people per hour per track.

I seem to recall some sections of 8 lane freeway in LA--chunks of
I-405, I think...

Now let's *both* look at reality.  You've assumed two things--first
that trains *will* be run at the kind of headways you're talking
about.  While you are (no doubt) correct that CalTrain (per your
example) *can* run 5 minute or less headways--do they?  I seem to
recall complaints about 2 *hour* headways at some times of the day...
The second issue is that, while you have cited *average* occupancy for
cars, you've cited full seat occupancy for the trains.  If I took the
daily ridership on CalTrain and divided by the number of trains--the
figures for trains would be lower, and I assumed that every car seat
is full (say--an average of 5 per car?) the freeway value would be
much higher.  In such a comparison, a freeway lane would yield nearly
10,000 people per hour, and a 4-lane freeway would be 40,000 per
hour--20,000 each way, while the train would fall to--perhaps--600
per hour.  Aren't statistics fun?

In addition, the need to run trains back to the start point empty in
many real-world scenarios ties up rolling stock, uses energy, wastes
crew time and has to be accounted for in the headways.  At least with
the car--the don't 'dead head' half the time.  (Yes--I know that
CalTrain simply stores many of the trains at one end of the line for
long periods of time--but that's the equivalent of parking cars which
Mr. Vandeman deplores so often--and much more valuable cars--each--at
that.)

	--Hal



-- 
Hal Heydt                    |    
Analyst, Pacific*Bell        |            You!
510-823-5447                 |    Out of the Gene Pool!
whheydt@pbhya.PacBell.COM    |
Xref: sparky ba.transportation:3107 rec.railroad:10491