The 405 and the fundamental law of traffic congestion

Matt Kahn discusses the lane closure on the 405 here. He refers to a very nice manuscript by Giles Duranton and Matthew Turner: the Fundamental Law of Road Congestion: Evidence from US cities who concluded that the provision of public transit is unlikely to have any impact on total vkt (vehicle kilometers of travel.)

I say this to my students and they go crazy because if there is one thing planners love, it’s transit. I love transit, too, but it is not really a way to address congestion except in very specific conditions, and then only for a short time period.

How can this possibly be?

It’s likely that vkt won’t change with transit supply for the same reasons that the road will eventually congest even if you provide additional road capacity. If there is sufficient demand for mobility on a corridor, you can serve some of that demand with alternative supply–like transit or telecommuting–and because those trips have shifted off the high-demand road, there are people who are now willing to drive on the corridor because it’s less costly in terms of time delays. The demand for road service and transit service work in tandem and people sort themselves based on preference, but it’s not like demand for the roadway goes way.

Now that doesn’t mean you have done no good. By serving more trips on transit, you’ve dampened vkt *growth*–you haven’t “eliminated car trips” the way many people suggest when they discuss transit provision. But by serving the existing demand on the corridor through parallel transit rather than new road capacity, you’ve probably (probably) made things better than they would have been had the additional supply come in the form of new road space.

So what about air quality? This is where it gets sticky. The outcomes depend on who jumps on the road when the transit passengers leave. If we take a bunch of high-income, new car owners off the road (Prius drivers even) and their trips are replaced by Silverados and POSs, then emissions can worsen from baseline conditions. Yes, I just outlined a scenario where transit provision made emissions worse. What if the new trips are made in hydbrids? Then we have probably lowered emissions.

But wait: it is also likely that even though traffic mix may change by shifting some riders to transit, emissions are probably less than if the additional trips on that corridor were served by new road capacity rather than transit.

There are other ways this scenario can play out. The key thing to keep in mind is that absent something that actively suppresses vkt or incentivizes fuel economy/emissions control, you do not lower overall vkt by providing alternative supply.

Transit supply is important even if it doesn’t always match our grand claims of “improving air quality.” It’s hard to improve air quality over baseline conditions without technology or emissions charges. Transit supply generally helps us by dampening emissions and vkt growth; which means we reduce what these might have been with road expansion rather than improve them from baseline conditions (which, when you think about it, still exist).

And shifted trips aren’t the only ones served by public transit; transit supply can draw its own demand, which increases mobility. It is value added there as well.

Not as sexy as “improves air quality,” I know. But maybe we can say “improves future air quality.”

Portland and Austin as congested small towns

HT to Getting From Here To There

I’ve always been troubled by the way the press reports TTI’s annual mobility report. The press generally hones in on one performance measure (aggregate delay) when TTI models a bunch of performance measures that seldom get any air time. Total hours of delay overemphasizes population at the expense of really looking at how much of the urban geography is actually congested most of the time. So Los Angeles is a high-population metro region, and if a whole lot of people experience relatively minor delays, the aggregate delay calculation can look bad when, in fact, the delay experienced by any given traveler can be pretty minor. It’s not that total delay is uninformative, it’s just that total delay is only one measure when we need multiple measures of system performance to figure out what is going on.

TomTom has released their list of the 20 most congested cities using data collected from their devices, and the maps are based on data they are collecting from their GPS devices. LA by these data is #2: Seattle is # 1. It’s helpful to measure congestion as a function of geographic or network coverage because that is the way drivers or transit riders actually experience it. It’s a performance measure of network saturation, albeit a rudimentary one.

So…with the caveats: We have to question the sampling validity of TomTom’s data–after all, we’re only using data on people who own TomTom’s devices. We also have to question their method of breaking up cities within the same region: Oakland is part of the Bay Area; Long Island is part of the New York metro; Alexandria, Fairfax, and DC are in the DC metro, etc. So counting those as separate cities doesn’t really make sense, and it affects the baseline of their percentage calculation.

But we should look at Portland and Austin in particular, as those are largely freestanding cities. Portland is ranked 19th, which is pretty low on the top 20, but it only has about 600,000 people and 20 percent of its roads are congested. Austin, Texas is 15th, with 25 percent of its roads congested at a population of a little under 800K. Now we need to think about this because Portland is routinely used as a model of development, and that includes density as a means of “fighting congestion.” This is internally inconsistent, and we can’t be doing this. If we are going to aim for density, we are also aiming for congestion.

It should interest us that four of top 20 cities are DC- area metros: Fairfax, Alexandria, Montgomery County and DC proper–are on the list, despite the region’s extensive provision of rail. Population and density increases–a change that planners are committed to–bring about congestion on all urban systems: streets, sidewalks, roads, etc.

My point? My point is that if the sustainable city has population density, it also probably has congestion once it gets good-sized. Most of the arguments for density in urban planning, other than the social ones, are economies of scale arguments: density means intensive use of shared space and services. That also means congestion once populations grow as space and service are usually capacity-constrained.

What’s the answer? We need to make peace with congestion–not the easiest answer to sit with.

Air quality, congestion, and pricing

One of my former students posted this story from the Wall Street Journal to Facebook yesterday. ARGH. Does the WSJ do no research in its reporting any more? So a time delay will shift drivers to transit but a charge for driving wouldn’t? Are WSJ reporters not required to understand basic econ anymore?

Congestion can be either good or bad for air quality depending on the geographic distribution of alternatives, the fleet, and the context into which the emissions enter. Congestion charging can in theory price trips onto the road under hypercongestion (the famous backward-bending demand curve), and thus may allow for greater VMT. But this is not true even in theory if the charging scheme is priced for VMT reduction or rationing rather than optimizing flow–those are different things, and the New York pricing plan was zone-based, so it most likely would have eliminated trips, not increased them! Higher throughput might affect emissions via flow optimization, but it is not apparent from either monitors or lab experiments that idling among a smaller number of cars/trips is objectively better for air quality than fast throughput from a larger number of cars/trips (and there may be a substitution effect in the traveling fleet that most people think is an air quality benefit; or there may be a freight effect which would not produce benefits [1]; we don’t know). Different types of emissions also vary with engine cycle, so it may be wash in total but a trade in emissions type.

Studies prior to the implementation of London’s cordon toll predicted fairly large reductions in emissions [2]. After the charge’s implementation, monitors throughout the metro area demonstrated statistically significant (though small in absolute terms) and progressively distributed improvements in pollutant concentrations [3,4]. Now, it’s not likely that we can attribute all of that change to the cordon toll, as accompanying the toll were rapid increases in bus supply (so much so that train trips also went down concurrently following the implementation of the cordon toll; I suspect that congested trains were traded for less-congested buses for short trips, particularly after the transit bombings in July of 2005).

Traffic calming, transit-oriented, density-based efforts in Paris—without the concomitant tolling efforts that London put down—have been found to increase emissions substantially, so New York may not be doing itself any favors with unpriced congestion [5]. Concentrations in some congested areas, like San Francisco, have not been improving as quickly as in other places. It may be that these simply reflect that when air quality is generally good in high-growth areas, reductions occur marginally more slowly than in places where concentrations are comparatively high. (IOW, it’s hard to improve on good.) However, it can also be that worsening congestion has caused higher emissions and that is being reflected in some regional monitors.

Some of the smartest transportation people in the world are at New York universities, but why would we actually CALL THEM to get some ideas for this WSJ peice? For most of these people, it wouldn’t even a long-distance phone call for the WSJ reporter. See? Look at this list! This is a dream team of people to ask rather than just talking out of your backside. BAD WSJ.

But then, as my friend Chris Redfearn once noted, discussions like this require people to keep more than one idea in their heads at once. If we are throwing around the “dubious” term, congestion on transit–and this exists virtually everywhere in the world that isn’t in the US–is most definitely NOT good for the environment: see Mexico City, see virtually every Asian city over 10 million people, and the many scooter engines on the road rather than transit trips.

[1] Marr, L. C. and R. A. Harley. 2002. Modeling the effect of weekday-weekend differences in motor vehicle
emissions on photochemical air pollution in central california. Environmental Science and Technology, 36:4099–4106.

[2] Beevers, SD, Carslaw DC. The impact of congestion charging on vehicle emissions in London. Atmospheric Environment. 2005 Jan ;39(1):1-5.

[3] Atkinson R, Barratt B, Armstrong B, Anderson H, Beevers S, Mudway I, et al. The impact of the Congestion Charging Scheme on ambient air pollution concentrations in London [Internet]. Atmospheric Environment. In Press, Accepted.

[4] C, Beevers S, Armstrong B, Kelly F, Wilkinson P. Air pollution and mortality benefits of the London Congestion Charge: spatial and socioeconomic inequalities. Occup Environ Med. 2008 Sep 1;65(9):620-627.

[5] Bouf D, Hensher DA. The dark side of making transit irresistible: The example of France. Transport Policy. 2007 Nov;14(6):523-532.

So how much is too much user charge for mobility?

I’ve subjected you to numerous rants about transport finance–including the fact that I think we over-invest in this sector–along with a question that haunts me…viz: who pays if transport system users don’t?

I sat down and frittered around with some numbers. The Institute on Taxation and Economic Policy derived some estimates for the out-of-pocket cost burdens for all major US taxes. I entered their data into a spreadsheet and then compared the estimated total burden for low-income households (which includes existing excise taxes) with estimates of a) system-wide HOT lane proposal for Washington, DC and b) a comprehensive, zone-based toll estimated for Paris designed to cut traffic by 25% (a big-ish toll, about $6 per zone). This is the result. The expected increase in total burden from HOT lanes is pretty small; the zone-based toll, however, is pretty large. c) and d) show the estimates of emissions charges compared to total tax burden. Those are really pretty marginal in the larger scheme of things.

Keep in mind these are just out-of-pocket costs. When you add in the benefits of congestion and emissions reductions, some estimates find progressive social welfare gains from pricing, even before you count revenue allocations. London’s cordon toll is pretty high and covers a fairly large swath of the urban environment. But the measured reductions in emissions following the cordon has resulted in sizable and steeply progressive air quality benefits for lower income areas of London.

So if we price the freeway, will the poor suffer? There is no easy answer to this question.

And another colleague weighs in on congestion pricing in LA

Peter Gordon also weighs in on the question of congestion pricing on the 710 in Los Angeles.

Actually, we should be precise, as this is a research blog. This is a value-pricing, not a congestion pricing scheme. Congestion pricing generally reflects an scheme that prices the whole facility. Travelers must chose between using the facility and paying, or not using the facility at all.

Value pricing concerns a subset of lanes that travelers may opt into. They can stay in the free lane and deal with congestion (or no), or they can pay into lanes that have been priced.

Marlon Boarnet on equity and toll roads

Marlon Boarnet has been one of my intellectual role models since before I went to graduate school. In today’s LA Times, he does a nice job of pointing out how superficial assertions about the equity of toll roads do not hold up. Bottom line: on public goods that are subject to congestion, there are only two things that discipline or ration use: out-of-pocket money costs and/or time costs. We can’t assume that favoring one or the other necessarily leads us to one conclusion about social equity. We can be pretty sure that impoverished families do pay proportionally higher out-of-pocket costs. We also can be sure that time burdens are also disproportionate, and we should never assume that less affluent individuals’ time is “free.”

In addition to Marlon, one of my colleagues from Industrial Engineering, Jim Moore, also weighs in intelligently, as does Kathryn Phillips–who is UCLA grad, like me–with Environmental Defense Fund also writes well here.

Large Eco-Village approved in the UK

The Architect’s Journal features a 195-unit Eco-Village, designed by Homes and Communities Agency (HCA) for the South Gloucester market. The development has everything, including a cafe and a creche (a bit too BF Skinner for me, but whatever) and a set of carbon neutral homes.

The part of this that makes me a bit sad is that while it’s a great idea, of course, the actual building designs are unattractive. Now, maybe it’s just me, and maybe I don’t understand the light and the context of the area (I’ve never been there), but I really wish architects would apply a vision to the available technology. Everybody thinks these innovations are a good idea; why can’t they be beautiful as well?

Congestion and the walking city

Paul Krugman notes on his blog that while he is favor of NYC’s move to turn Times Square into a walking only area, he’s not sure who the move is for, as “nobody goes there-it’s too crowded.”

Krugman references my favorite quote about congestion from Yogi Berra. As Brian Taylor pointed out in a very good paper in the Journal of the American Planning Association, Berra captured an essential conundrum from urban economics for urban planning newfound efforts to “contain sprawl.” That contradiction comes down to a) congestion is a sign of a successful place within cities (the “it’s too crowded” part), at the same time b) that same congestion and place intensity provides the demand for decentralization–the “nobody goes there” part.

This contradiction makes it difficult to deliver on the “congestion relief” promises that many people make on behalf of compact urbanization— one of the key elements of sustainable city ideas. Los Angeles may be everybody’s favorite whipping boy for auto congestion, but DC, New York, Boston and Chicago all have congestion both on the road and elsewhere: there’s never a seat any Starbuck’s off DuPont Circle, for example, and the sidewalks are uncomfortably crowded in New York at certain times of day. The Mexico City subway or the trains in Japan–or in most global cities other than LA—are simply jammed.

I’m not saying that auto congestion is the same for the environment as these other forms of congestion–it’s not–but as Taylor points out, places that we sustainable urbanists love–like New York–have pretty bad traffic congestion, and that traffic congestion is part of the place’s vibrancy and a measure of its success–not its failure.

Thus our sustainable cities of the future are likely to be crowded–very crowded if population growth continues. Most Americans, even those who live in New York, have no idea what real megacity crowding is like. The the demand for decentralization will grow stronger as we densify, even as we try to pack a whole bunch of amenities into our compact, walkable new developments, so long as there is income and wealth to support purchasing more space in a crowded world.

Taylor, Brian D. 2006. “Putting a Price on Mobility: Cars and Contradictions in Planning,” Longer View, Journal of the American Planning Association, 72(3): 279-284.