Public Interest Transportation Forum,

Bus Rapid Transit vs Light Rail
in the

Metropolitan Puget Sound Region

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 Atlanta (shades of the Oklahoma Sonics).  One would think that nothing had changed since The Beatles released Magical Mystery Tour.  But forty years ago there was no Microsoft, no Google, no Internet.  Likewise in transportation, time has not stood still over the last couple generations.  In fact, while it apparently has escaped many, there has been a transportation revolution in the interim. ONE In exactly the same way that major classes of pollutants have been cleared up via the creation of markets for these “bads”, so we have at least the beginnings of a market mechanism whereby  traffic congestion can be tamed via “mobility pricing”.  The most famous application of this technology is in central London where a cordon charge has allowed buses and delivery vehicles to move about much more freely.  More pertinently, and closer to home, HOT lanes have been put in place in San Diego, Houston, Denver, Minneapolis, and even here in the metro Puget Sound on SR 167, where we are currently working out the inevitable start-up kinks in the system. 


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.


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 Manhattan, the truth is 180 degrees opposite that of my callow proclamation. 


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 (Hong Kong) to several minutes.  If the headway is every three minutes, then the passenger through-put is 20 trains per hour  times the potential number of passengers per rail car (either seated or seated plus standing) times the number of cars per train.  Things that lengthen the headway included “interleaving” trains (for example one coming from the east, one from the south, one from the east, like the Link light rail plan), and having trains run in other than a fully “grade separated” manner (again, like Link, which will  travel at grade south of downtown Seattle).  Things that limit the number of cars per train include running “at grade”, since you don’t want to block the intersections (Link again) and the length of the stations themselves.  Typical heavy rail trains consist of up to 10 cars.  Link is limited to a maximum of four. 


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 Manhattan and New Jersey, buses run at a rate of just under one every five seconds, which we will take as the upper limit. SEVEN  Now it’s only a matter of multiplying that number of buses (one bus every 5 seconds = 720 per hour) times the number of seats (or seats plus sanding positions) to get potential throughput.


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.   


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 Paris.  The French for instance.  They are busy escaping to the suburbs as fast as their income allows, and in spite of $9 a gallon gas.  But let’s assume that at least modestly concentrated, “walkable” neighborhoods are the way to go:  downtown Kirkland as opposed to the (mostly empty) Totem Lake shopping mall.  For this you need transit because if everyone shows up in a car and parks, especially in surface lots, you end up with the area around Southcenter: no pedestrians allowed.  Downtown Kirkland (and the similar Madison Park) have transit connections, albeit modest ones, and they both are eminently walkable.  If, due to the desire to concentrate development further, more transit is required, a facility such as the Third Avenue transit mall or the Downtown Seattle Transit Tunnel (especially if it were tweaked for optimal bus operations) TWELVE works perfectly well.  Toronto, Curitiba, Pittsburgh and Bogota all show that it’s totally feasible to concentrate development via BRT.  Contrariwise, development along Portland’s light rail system is mostly due to subsidization.  And where is the concentrated development induced by the heavy rail system Atlanta “stole” from us?  Nowhere, that’s where.  Seattle, with buses, has done better in this regard than Atlanta with rail. THIRTEEN


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


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.  





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.

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.  


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.


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


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. According to Sound Transit’s “Regional Transit Long-Range Plan”, DEIS, December 2004, Figure 4.9-10 (page 4.9-26), light rail on the I-90 bridge could ultimately have headways as low as 5 minutes (ie, 5 minutes per train).  footnote 24

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 3456 seats per hour / 61 seats per bus = 58 buses per hour, round up to 60 per hour, or one per minute.



9. If you’re taking public transit from Redmond to downtown Seattle, you’re going to want to be able to sit down!  This is also the transit policy for the region.


 10. A lane dedicated to buses can carry one bus per 5 seconds (footnote 6).  To equal LRT, BRT on I-90 would need only one per 60 seconds (footnote 8).  5/60 = 1/12.


 11. Among pricing wonks, what constitutes a “qualifying carpool” is a matter of much discussion.  The two bookends are a) HOV3 (three or more people per vehicle, since at HOV2 the lanes bog down during rush hours, and b) vanpools or better (only official vanpools and buses qualify, all others pay).  Of course at the second bookend, the per person charge for a 3 person carpool would be 1/3 of the charge for the vehicle.  Most such wonks favor “vanpools or better” since it is much easier to enforce, and, once set, it need never be changed.  The argument in favor of HOV3 is one of “fairness” (which, as every parent knows, is a hard concept to get agreement on).


Note that in the case of I-90, Mercer Island vehicles might get a special break, depending on how the politics of the matter play out.


12. Tweaking the DSTT for optimal bus operations would entail slightly widening the travel lanes at the stations so that a bus could pass while another is stopped at the station. 

See  footnote 22This document is a slightly expanded version of the following OpEd:


13. Until recently Bay Area cities with BART stations had less concentrated development than those without!





15. On the other hand I would ride an elevated bus-on-rail system like the O-Bahn in Adelaide, Australia, a kind of a rail-bus hybrid pictured on the left, in preference to a light rail system, since it has the flexibility of bus plus the grade-separation of heavy rail.  (Aurora Avenue would be a good place for such a bus-on-rail system.)


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