Re: Why no TV?

Keith F. Lynch <kfl@xxxxxxxxxxxxxx> wrote:
> Brian Henderson <BrianL.Henderson@xxxxxxxxxxxxxxxxxx> wrote:
>> "Keith F. Lynch" <kfl@xxxxxxxxxxxxxx> wrote:
>>> You can also listn to CDs on a bus or train. And you can *read*.
>
>> You can only do so through headphones, or unless you want to impose
>> your music choices on everyone and be rude.
>
> True.
>
>> And I can't read in a vehicle, moving or not.
>
> So? Most people can. Most people I see riding Metro are reading.

My wife is, unfortunately, not one of the most. Reading in a moving
road vehicle makes her vomit. Trains are marginal and airplanes seem
to be OK.

>>> If there were buses running every five minutes on each major
>>> north-south road, and other buses running every five minutes on
>>> each major east-west road, *instead* of all those cars, it ought
>>> to be possible to get around much more quickly, with at most one
>>> transfer between any two points.
>
>> That assumes that you're only talking about a couple north-south and
>> east-west roads, not hundreds.
>
> One every half-mile or so, meaning that a bus stop would never be more
> than about quarter mile from anyone.

But it's the stops that boost travel time. The light rail here stops
roughly once per mile (25 stops in 28 miles) but it's enough to cut the
average speed to 25 mph despite large portions of the trip being at 65
mph. Local buses are even slower (average about 15 mph) because of the
30-40 mph maximum on most of the streets. Doubling the number of stops
would make it even worse. And no, the slow speed for the buses is not
due to traffic. The difference between early morning (streets empty) and
rush hour is three minutes on a 50+ minute trip. Using a strict grid
system and no freeways a trip that's currently 46 miles and 70 minutes
by car could be 60 miles and 3 hours. Likely worse if there's a
substantial number of people getting on and off at the stops.

>> The number of busses required would be ridiculous, simply because
>> you're looking at moving thousands of people going thousands of very
>> different locations.
>
> The number of busses required would be less than 1% of the number of
> cars needed to move those people if they each drove their own car.
>
> As I said, with one transfer it ought to be possible to get from
> anywhere to anywhere else in the same city or its suburbs with at
> most one transfer.

Possible, as long as you place little or no value on your time. Let's
try an example. You have two points that currently lie near a freeway.
Travel distance is 40 miles and travel time is about 60 minutes. We'll
be pessimistic and say 90 minutes during rush hour. On a grid system
the travel distance ranges from 40 to 56 miles. We stop every 0.5 miles
for 30 seconds. In between stops we average 30 mph. So, our driving time
is 80 to 112 minutes, our stopping time is 40 to 56 minutes and our
total trip time is between 120 and 168 minutes. The bus costs between 30
and 78 minutes extra each way, assuming I'm travelling at rush hour and
I have zero waiting time for the original bus or the transfer.
As a reality check, I just compared drive time from the rail station
closest to my house to the college where my wife is working, which is
served by bus from the rail station at that end. Drive time is given as
50 minutes and best case rail/bus time is 108 minutes. The trip consists
of light rail feeding directly into a bus route that only has 4 stops and
with only 5 minute gaps at the two transfers.

>> I know you're aware LA doesn't have such a system, I'm just saying
>> that it's an unrealistic system to begin with, even if they could
>> somehow build the thousands of busses required to do it in the
>> first place.
>
> They can build tens of millions of cars, but not tens of thousands
> of buses?

Build, of course. Use efficiently?
Another quick calculation. Assuming a grid of 80x40 miles (DFW), an
average speed of 20 mph, a 1/2 mile grid spacing and a desire for no
more than 15 minute wait time, how many buses have to be on the road
at the same time? I get 320 bus routes in one direction and 160 in the
other (have to go both ways). A 15 minute wait time at 20 mph implies a
bus every 5 miles, so 16 buses on each of the 160 80 mile routes and 8
on each of the 320 40 mile routes. We need 5120 operating buses to
implement this system. The data I found for Dallas is from 1996, but
gives the operating cost for a bus as $72.76 per hour. Using this (and I
doubt the cost has gone down) we get an operating cost of $372.5K per
hour of operation for our system, or $3.26 billion/year to run the
system 7x24. And we still get utterly miserable performance. Additionally
the estimate is probably far too low. For one thing, it ignores the peak
load of the system at rush hour. A completely packed bus might hold 70
people, but at peak you're going to need to move at least 2.5 million
people in a two hour period. Even with optimal distribution you're going
to need 4 to 6 times more buses in operation at once.

>> And then you'd end up with bus gridlock.
>
> With one bus every five minutes per road per direction?

I was assuming a bus every 15 minutes. If we switch to one every 5
minutes you'll need to triple the cost. Of course that helps you on the
peaks, but raises your operating cost to $10 billion a year. And you
still get miserable performance (6 hours to cross the metro area?).

Robert
--
Robert K. Shull Email: rkshull at rosettacon dot com
.

Relevant Pages

  • Re: Why no TV?
    ... miles) but it's enough to cut the average speed to 25 mph despite large portions of the trip being at 65 mph. ... Even if you assume a stop every half mile, you could never really get the bus up to any speed. ... You now have 10 minutes left to travel those 25 miles and average 25 mph. ... That's quite an acceleration for a bus, though not impossible, and has us peaking at VERY unsafe speeds for any residential or urban locations. ...
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