Public Interest Transportation Forum, www.bettertransport.info/pitf
Bus Rapid Transit vs Light
Rail
in the
Metropolitan
Guest Essay by Don Padelford
Well, here we go again, with
a Proposition 1 (Roads and Transit) do-over, or at least the Sound Transit
(largely light rail) portion of it. A commentator
in
Crosscut (Ben Schiendelman) writes that, contrary to the analysis of former
Washington State Secretary of Transportation Doug MacDonald (also
in Crosscut), rail is
just what the doctor ordered for what ails the region. His arguments are familiar: transit mobility, capacity, reliability, and economic
concentration, all allegedly superior with light rail (LRT) compared to Bus Rapid
Transit (BRT).
Transit Mobility
It’s kind of amazing the
extent to which this debate is framed by a vote 40 years ago when “our” heavy
rail system decamped to
Many have completely missed
the import of this revolution in transport, which, once it is rolled out and
fully implemented, holds out the prospect of eliminating transit congestion (and
eventually all congestion
TWO) over the 150 or so miles of the regional freeway
network. Combine
this with bus-only lanes on major arterials (taken, where possible, from the
parking strip
THREE ), and the task of
achieving transit mobility is largely accomplished.
Since private commuters would
be more than happy to pay the price of a double tall latte for a congestion-free
commute, conversion from HOV to HOT status could be achieved at no public cost whatsoever
(FOUR ), and could be accomplished within a decade from whenever
the consensus forms to go ahead with the conversion. Compare this with a light rail system
covering the same territory, which would take (who knows?) possibly a century to complete at
the cost of perhaps a couple hundred billion dollars. To summarize, by applying market
forces in service of transit mobility, it would be easy to achieve BRT mobility
throughout the entire metro region, at little cost to the general public, and
in a matter of years. That
is, if we can get over our infatuation with rail.
Capacity
The next issue is capacity. If you have ridden
BART or a similar heavy rail (FIVE) system, it is understandable if you have formed the notion
that rail has more capacity than Bus Rapid Transit. I confidently proclaimed exactly this
conclusion to a transportation economist a couple decades ago, at the beginning
of my education on this issue. He looked at me the way you would a
small child, gently cleared his throat,
and then set about explaining the facts of (transportation) life to me. Except in exceptionally
space-constrained locales like
Here’s why. The potential through-put of a transit
system is pretty easy to calculate. It is the number of transit vehicles (bus
or train) you can put down a track or lane per hour times the number of passengers each vehicle can carry (in the case
of a train, the vehicle may consist of several “cars”). The big constraint on the system is
what happens at the station.
Think of a train. It pulls into a station, discharges passengers,
takes on passengers, and leaves. Then, some time later, the next train
pulls in. The
time between the first and next train is called the “headway”, and, depending on
a number of factors, it can be anywhere from 90 seconds (
On the BRT side of the equation
the limitation on through-put is also dictated by what happens at the station. Where buses operate
like trains, with a bus in a station blocking following buses, the same
calculation as above is made.
However, unlike trains, it is common practice to unload and load
BRT buses out of the traffic flow (“off-line”). In that case
the number of buses per hour is limited by how closely you can space them in
the traffic lane.
SIX
In the Lincoln Tunnel between
I will leave the math for a
footnote,
EIGHT but in the case of Link LRT over the I-90 bridge, at maximum build-out
and use (decades and billions and billions of dollars from now), it could potentially
carry the seated
NINE equivalent of one bus per minute. Since a facility dedicated to buses could,
if transit demand were ever to materialize, carry twelve times that number (one
every five seconds), it is a simple fact that on this facility BRT has an order
of magnitude more potential capacity than LRT. As my friendly transportation
economist showed a younger me a couple decades ago, you just have to do the
math.
Reliability
The third issue is
reliability. According
to Sound Transit (and others), in order
to equal the reliability of rail, buses have to have their own lanes, and the
problem with this is that it’s easy to grab a can of paint and let cars onto
the roadway, thereby eliminating bus reliability. This view is captured in the often-heard
statement that the problem with buses is that they “just get caught in
congestion”. Sometimes
they do, sometimes not.
It depends.
Buses on HOT lanes don’t get
caught in congestion, because, to the extent they need it, all other vehicles
are ejected from the lane.
For this reason HOT lanes are sometimes called “virtual exclusive
transitway” (VET) lanes.
When they need exclusivity, they get it. But since, as described above in
relation to I-90, they generally only need a small fraction of a lane (1/12th
of a lane’s worth to equal the throughput of light rail on I-90
TEN), the balance
of the VET lane can generally be used by vanpools, qualifying carpools
ELEVEN, trucks and
other vehicles. Therefore, under most circumstances, the vast majority of the
lane capacity would be available to non-transit vehicles.
Of course this is not true of
bus-only lanes on arterials (although, depending on design criteria, these
lanes would be shared with right-turning vehicles). But as with freeway HOT lanes,
arterial bus-only lanes ensure that buses so not get caught in congestion.
In conclusion there is no reason why a
properly designed BRT system running on freeway HOT and arterial bus-only lanes
cannot equal or better (due to the fact that a stuck train cannot be bypassed
while a stalled bus can be) the reliability of LRT.
Economic Concentration
The fourth issue is the
ability of transit to concentrate development. There are a number of things to be
said about this. The
first is that not everyone wants the extreme concentration found in the
tourist’s
One statement sometimes made
about buses is that people just won’t ride them. But in a recent discussion on public access
TV Mike O’Brien of the Sierra Club stated that we need rail because the buses
are too crowded.
FOURTEEN So I guess we need
to modify the statement to read, ‘no one will ride buses because they’re just
too damn crowded’! There
does remain a perception that rail is, as our mayor has so alluringly intimated,
more “sexy”. But
is this a sufficient reason to pay ten times the per mile cost for transit mobility? Surely the average,
hard-pressed taxpayer does not believe this. If Paul Allen had subsidized the full
increase in capital and operating costs between a bus line and the South Lake
Union Trolley (instead of just a portion of the former and none of the latter),
well fine. Like
others, assuming all things are otherwise equal, I would “ride the slut”
instead of a bus. But, as seen above, things are in no
way otherwise equal.
FIFTEEN
Conclusion
So, in my view none of the
arguments favoring Light Rail hold up At least for this metro region , BRT
on freeway HOT and arterial bus-only lanes is the way to go. It will give us
much more transit mobility for the buck, it has far more capacity, with equal
(or better) reliability and ability to concentrate development. We should reject
Sound Transit’s Prop 1 Do-over, and build a true twenty-first century transit
(and transportation) system.
Links
1. http://community.seattletimes.nwsource.com/archive/?date=20020509&slug=tolls09
2. One can eliminate freeway
congestion by “mobility pricing” all freeway lanes. One thing that is not generally
recognized is that doing this would substantially increase effective rush-hours
highway capacity. The
reason is that a freeway in semi-gridlock cannot carry many vehicles. In a sense a
highway in this condition “stalls out” like an airplane wing, losing half or
more of its effective capacity. In a seeming paradox, by limiting
instantaneous access to a highway (not letting it “stall out”), one can
increase its capacity, which therefore increases access.
Another approach, which the
Puget Sound Regional Council has studied in depth, is to “mobility charge” all roadways.
http://www.psrc.org/projects/trafficchoices/summaryreport.pdf
If the net revenues from
pricing were distributed to the region’s voters per capita, most people would
make money from this strategy. And since the wealthier generally
consume more than “their share” of rush hours roadway space, the net result
would be mildly “progressive” in an income redistribution sense.
3. Where a lane is used for
parking, it would be annexed for buses. However, since parking is the
“mother’s milk” or retail it would be necessary to more than make up for the
foregone parking spaces, replacing them, perhaps on a 2 for 1 basis, with lots or
garages every block or two.
To keep vehicles other than buses off the bus lanes, arms like
those found in parking garages would be spaced along these lanes. The actual bus
stops could be located to the right of the bus lanes (“inset” into the block). Right-turning
vehicles would be allowed in the bus lanes, but, of
course, they would have to exit prior to coming to a parking-garage-type arm.
4. Which doesn’t mean that
completing the HOV lane system, something the region is committed to do in any
event, would be costless.
Over two-thirds of this system has been built, and most of the
balance is funded. The
most difficult, and expensive, section will be the current express lanes
between downtown Seattle and Northgate.
BACK
5. “Heavy” rail systems, like
BART, are totally grade-separated. The “light” in light rail refers not
to the weight of the trains (they are generally heavier than heavy rail), but
to capacity. They
are light-weight in terms of capacity.
BACK
6. Capacity of a route or of a group of routes on the
same facility is almost always determined by
conditions at stops areas rather than line conditions. ... When stops are made off the main line or artery, capacity is determined
by the safe separation between transit units. Thus, on exclusive busways or bus
lanes on freeways, with off-line bus stops, headways of 5 s[econds]
can be achieved. Theoretically rail systems could operate at headways of
perhaps 60 s[econds] under similar conditions, but
such situations are not found in practice. -- Highway Capacity Manual
BACK
7. The Lincoln Tunnel bus lanes
are burdened by a difficult merge. If this were resolved, the facility
would be able to carry additional traffic. But using the this facility as the
template, the seated capacity of a bus-only lane, or a HOT lane that has become
a de-facto bus-only lane due to extraordinary demand, is:
1 bus per 5 seconds x 3600 seconds per hour x 61 seats
per bus
= 720 buses per hour x 61 seats per bus
= 43,920 seats per hour.
8.
http://www.bettertransport.info/padelford/DSEIS%20ST2%201204.htm
One train every 5 minutes =
12 trains per hour; each train could have as many as four cars; and each car
could have as many as 72 seats:
12 trains per hour x 4 cars per train x 72 seats per car = 3456 seats per hour
per direction (compare with the bus number, 43,920 in footnote 7).
Hybrid buses have 61 seats,
so to equal light rail, BRT would need
9.
BACK
BACK
Note that in the case of
I-90,
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12.
See
http://seattletimes.nwsource.com/cgi-bin/PrintStory.pl?document_id=2002619155&zsection_id=268883724&slug=sunpadelford13&date=20051113
BACK
13.
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14.
15. On the other hand I would
ride an elevated bus-on-rail system like the
O-Bahn in
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Last modified:
February 07, 2011