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Dr. John Holtzclaw (Presented at the Air & Waste Management Association's 90th Annual Meeting & Exhibition, June 8-13, 1997, Toronto, Ontario, Canada 97-TP60.02) Introduction Motor vehicles are the single largest source of air pollution and a major source of water pollution. In the San Francisco Bay Area, for instance, on-road vehicles emit 40% or the reactive organic gases, 38% of the NOx and 69% of CO.(1) In the U.S., tailpipe emission standards have not been tightened for years, with no regulations to tighten them in sight. After heavy lobbying by auto manufacturers, California relaxed its rule that required new car sales to include a few percent of Zero Emission Vehicles. It=s hard to be optimistic that emissions standards will improve much in the near term. After leaving the assembly line auto emission systems deteriorate and must be maintained to keep emissions low. Yet legislators shy away from requiring more effective inspection and maintenance programs, such as centralized inspection, loaded-mode tests, higher mandatory repair limits and diesel standards, in all state non-attainment areas. Talk radio even raised a firestorm in San Francisco against cleaner-burning reformulated gasoline. Nor are evaporative emissions or entrained dust even addressed by tailpipe controls. There appear to be real political limits to more effectively cleaning up the car. Yet, auto ownership and vehicle miles traveled (VMT) continue to grow. U.S. VMT grew at rates well over 3 percent per year during the 1980s, and is forecast to increase 25 percent per capita between 1990 and 2010.(2,3) Hidden subsidies to motor vehicle use are estimated to range from $3 to $7 per gallon of gas, yet discussion of charging drivers the full cost of driving by raising gas taxes, converting free to toll roads, instituting smog fees or eliminating free parking runs into widespread opposition from corporate interests.(4-9) Present auto subsidies include road construction and maintenance not covered by gas taxes; police, fire and ambulance services to motorists; taxes lost on land cleared for freeways; free parking; pollution; noise and vibration damage to structures; global warming; protecting the petroleum supply line; production subsidies; sprawl and loss of transportation options; uncompensated auto accidents; and congestion. Even mild measures aimed at reducing single occupant vehicle commuting meet formidable resistance. Lobbyists stripped from federal law the employee commute options mandate that required employers to design programs that would modestly reduce single occupant vehicle commutes in non-attainment areas. The California legislature even denied air districts the right to implement such trip reduction ordinances. Few employers offer non-driving commuters cash payments equal to the free parking they give drivers (parking cash-out). Can Urban Form Be Harnessed to Reduce Driving? Given the problems confronting reductions in tailpipe emissions, even as mileage and congestion continue to increase, what alternative approaches are promising? Recently, many urban planners and architects have suggested that returning to traditional city and neighborhood design could reduce auto ownership, VMT and cold starts. Traditional cities grew up around pedestrians, and residents could conveniently walk, bicycle or take transit to most jobs. These neighborhoods had corner markets and other nearby commerce. They were so complete that many residents seldom left them. These areas are now the central and adjacent areas of our older cities and some of the older suburbs. Some are abandoned. Could restoring these areas benefit air quality? The hypothesis to be tested is that increased convenience, pedestrian amenities and transit service in our neighborhoods would decrease driving and cold starts by increasing accessibility. Increasing density and allowing mom and pop groceries, restaurants and other neighborhood businesses in residential areas, and locating these areas close to employment centers, increases accessibility for residents. But would such design effectively reduce driving in modern America, where unfettered motoring down an empty country lane is our transportation standard...or so new-car commercials would have us believe. The issue is controversial, with homebuilding-industry sponsored studies purporting to show that the suburbanization of jobs results in suburbanites having shorter commutes, and presumably driving less than residents of traditional neighborhoods in central cities.(10,11) To address this issue we first identify the characteristics of traditional neighborhoods. These areas have relatively high densities: ranging from row houses on narrow lots through 3 to 4 story walk-ups to high-rise elevator apartments, condos and co-ops--at 20 to 200 households/residential acre. They are proximate to major job and shopping concentrations. They have a wealth of local shopping and services, and sidewalks and other amenities to encourage walking. They have excellent access to transit. Various mixes and matches of these characteristics have been identified and measured by the pioneers in this research, including Bob Cervero, Michael Replogle and Larry Frank.(12-14) Now that we have identified the characteristics of traditional neighborhoods we can test the hypothesis that they lead to lower auto ownership and driving. The evidence to test this hypothesis has been rather scant, often based on such inappropriate measures of total driving as commute times, even though commutes are only 1/4 of total trips, and walking commutes would show up as longer commute times, implying longer trips or more traffic congestion. Rather than analyzing neighborhoods, some studies dichotomize central cities versus suburbs, even though some suburbs are older and traditional, while some central cities such as Houston or Phoenix don't qualify as traditional neighborhoods. This practice reflects the difficulty of obtaining detailed data on the wealth of neighborhoods that populate our urban areas. To get around this problem some studies have compared neighborhoods that are selected to be representative of traditional/central city or modern suburban areas. Recent Research In California My own 1991 and 1994 research falls prey to the last question--of representativeness. In the first study, for the Natural Resources Defense Council (NRDC), I analyzed five communities in the San Francisco region selected to cover the full range of neighborhoods, from traditional to suburban.(15) They included 100 household/residential acre northeast San Francisco (Nob, Russian and Telegraph Hills, Chinatown and North Beach), where I live; the whole of San Francisco at medium-high density; medium density Rockridge district of Oakland, with a BART station; the densifying suburb Walnut Creek, also with a BART station; and a low density modern suburb San Ramon, at 3 households/residential acre. I found that high residential density, nearby shopping, good transit and a good walking environment go together. And, alternatively, sprawling suburbs isolate stores into shopping centers, have poor transit service, and often don't even have sidewalks. The co-variance of all these variables increases the difficulty of disentangling their effects, but does allow density to serve as a surrogate for the group of variables to some extent. I obtained automobile ownership from the 1990 U.S. census. Accurately measuring VMT is usually a major shortcoming of travel studies. Where would you get accurate measurements of thousands of people's driving? We used odometer readings recorded when auto owners took their cars in for smog-checks. I found that residents of higher density communities drive less. Comparing the extremes, the Nob Hill area was found to have 32 times higher household density, and 200 times higher local shopping than suburban San Ramon, while only about 1/4 the household auto ownership and VMT. The 1994 study included additional San Francisco neighborhoods and Los Angeles, San Diego and Sacramento neighborhoods.(16) These 27 neighborhoods were identified with the help of the Association of Bay Area Governments, the Southern California Association of Governments (SCAG), the San Diego Association of Governments and the Sacramento City Planning Department. These neighborhoods were selected to represent the communities in the regions based upon the judgement of regional planners. Both studies found that the average resident in a neighborhood will drive 20 to 30 percent less per capita or per household than the residents of another neighborhood half as dense. In other words, if you live in a neighborhood twice as dense as your sister's neighborhood, on average you and your neighbors will drive 20 to 30% less than she and her neighbors, whether you both live in low density areas, middle or high. While this seems like a modest difference, it can really add up. The Nob Hill area is 32 times denser than San Ramon, or 5 doublings, giving it only 32% as much VMT if driving drops 20% as density doubles, or 17% as much at 30% reduction. The 0-5 household/residential acre densities of most post-WWII suburbs could be doubled 7 times to equal many Manhattan neighborhoods: 400 households/residential acre. At 30% reduction in driving as density doubled, the Manhattan families would drive only 8% as much as the suburbanites. That's a huge decrease in air pollution. This general pattern has been found in New York, Chicago, Toronto, and across U.S. and British cities, however using data for whole boroughs, cities, or urbanized areas, or using transportation modeling to estimate VMT, rather than direct measurements. The second study gave similar results, and covered sufficient neighborhoods to get statistical significance. The strongest reductions in driving were found to be due to residential density, followed by the quality of transit service. Doubling residential density was shown to lower auto ownership 16%. Doubling residential density was shown to lower VMT 16%, while doubling public transit service reduced VMT an additional 5%. When density was considered as the surrogate for all the variables, doubling residential density resulted in a 20% reduction in VMT. The other variables, local shopping and pedestrian friendliness, acted in the predicted direction but with less force. The present study, again sponsored by NRDC, along with the Center for Neighborhood Technology (CNT) in Chicago, and the Surface Transportation Policy Project in Washington, DC, expands the previous studies to include every neighborhood in the San Francisco, LA and Chicago areas. The measures of traditional neighborhood characteristics are residential density, center proximity, local shopping, transit service and pedestrian/bicycle friendliness. Auto ownership is again obtained from the census and VMT from odometer readings taken during smog checks. The study has produced preliminary results using density as a surrogate for the cluster of co-variant variables, and crude measures of transit service in the Chicago area. These results use household travel surveys to measure auto ownership, VMT and trips by private vehicle. The surveys were compiled by the regional transportation planning agencies--the Chicago Area Transportation Study and the Metropolitan Transportation Commission--from 1-day travel diaries. In a household travel survey a randomized sample of households is contacted and asked to participate. A fraction of those contacted agree to participate, and a fraction of these actually complete and return the diaries in usable form. Commonly around half the households initially contacted end up participating successfully. If there is a response bias, it is probably weighted toward the better educated households. The resulting sample of 10 to 20 thousand households represents 1% of the region's total households. In the San Francisco area there are fewer households in the few high density zones than would be desirable for some multi-variate analyses. Yet these surveys are adequate to strongly support the earlier analyses. The non-linear regression analysis for Chicago, again using density as a surrogate for the cluster of neighborhood characteristics, gives a 9% reduction in auto ownership and 14% reduction in VMT every time density doubles. Regressing density and transit service together gives a 15% reduction in VMT every time density doubles, with a further 7% reduction in VMT every time transit service doubles. Average daily driving and vehicle trips were calculated for households in the San Francisco household travel survey, at 0-2 households/residential acre, 2-5, 5-10, 10-50 and above 50. The results show a 21% reduction in auto ownership, 30% reduction in VMT and 23% reduction in vehicular trips every time density doubles, Figures 2 and 3. At a 30% drop in VMT as density doubles, the Nob Hill area's 32 times higher density predicts that it would have 17% of San Ramon's VMT/household. Vehicle trips per household, while not a precise measure of cold starts, are our best approximation. And at a 23% reduction in vehicle trips as density doubles, the Nob Hill neighborhood produces only 27% as many cold starts per household as San Ramon. These results indicate that an urban development strategy of building traditional neighborhoods could substantially reduce driving and vehicular emissions. Some very preliminary analyses of SCAG's travel analysis zones in Los Angeles use census data and a preliminary estimate of VMT based upon smog-check odometer readings. They show an 18% reduction in both VMT and vehicle ownership as density doubles. But could income effects be masquerading as density effects? Studies have shown that wealthy households own more cars and drive more. Could it be that the wealthy have all moved to the suburbs? Not that anyone who had priced million dollar Nob Hill condos would believe. Let's again visit MTC's household travel survey. It confirms that the wealthy drive more, Figure 4, but shows that they drive 29% less as density doubles, compared to 37% less for the middle class and 35% less for the poor. The impact of density is strongly confirmed. The tragedy is that even the poor living at low density have to invest so heavily in auto use. Applying These Predictions To Existing Built-up Regions Ok, the skeptic says, but our suburbs are already built and we are not going to tear them down to rebuild in traditional neighborhoods! That's true, at least in the short term. However 50 to 75 year-old suburban housing is often a candidate for demolition and replacement. So there is plenty of potential in the long term. But consider only the short term--what benefits a policy of spurring traditional development in a built-up region might yield in a mere 15 years. As the Metropolitan Transportation Commission (MTC) was developing its 20-year Regional Transportation Plan (RTP) for the San Francisco Bay Area in 1993, it soon became obvious that no non-highway alternatives were to be considered. So the Regional Alliance For Transit (RAFT) -- a transit and environmental coalition -- proposed to define a pedestrian- and transit-oriented alternative. MTC analyzed it in their modeling system. RAFT sought to increase accessibility to transit, especially by foot and bicycle. So RAFT assumed the same total regional population and job growth as MTC, but clustered the projected growth of households and employment after 1995 around transit stations at higher densities. By developing in areas with existing infrastructure -- schools, public facilities, streets and utilities, the region could save itself up to $25 billion on construction of these facilities. And save some 200 square miles of forests, grasslands and farmlands that MTC's alternative would sacrifice to development of residences, commerce, industry and local streets. RAFT designed transportation improvements which eliminated nearly all of MTC's 500 new highway lane-miles, and put the savings into cost-effective public transit. It stressed rail improvements in the urban corridors, including extending the CalTrain, which now runs from south of San Jose to San Francisco, a mile and a half to San Francisco's downtown Transbay Terminal and electrifying the system, new light rail lines in San Francisco and Santa Clara counties, new heavy rail on existing tracks to link Santa Clara light rail to East Bay BART and on to Livermore, Sacramento and San Joaquin county, and new commuter rail in Marin and Sonoma counties. It also included new electric trolley-buses in the East Bay urban corridor between Hayward, Oakland and Richmond, and express buses on I-80 and I-680. Having improved CalTrain service to San Francisco Airport, it eliminated the parallel, more expensive, BART extension. It converted some freeway lanes to bus/carpool lanes. Further, in order to slightly reduce the $3 to $7 per gallon of gas subsidies to driving, it assumed parking cash-out, whereby non-driving employees receive the cash value of their unused "free" parking. California law allows county congestion management agencies (CMA) to mandate parking cash-out. So the RAFT alternative included this one market-based measure along with the increases in density and transit service. MTC input this alternative into its modeling system, see Figure 1. They predicted that by 2010 RAFT's alternative would reduce regional VMT 6% below MTC's alternative, saving the average family 1,148 miles of travel annually. This is worth $379 annually to the average family, using FHWA estimates of auto costs.(17, 18) RAFT would save 350,000 gallons of fuel daily and cut mobile source particulate emissions 10%, carbon monoxide 4%, reactive organic gases 5% and nitrogen oxides 5%. Further, RAFT would cut congestion by 13%. These results come after only 15 years of changing to traditional development patterns. Consider the magnitude of the impact after 50 years of these patterns! Further, RAFT would boost transit passengers regionwide by 24% over MTC's alternative, including Muni Metro 29%, CalTrain 167%, Santa Clara light rail 76%, East Bay heavy rail (Amtrak) 152%, and AC Transit 39%. It would boost BART patronage 15% higher than MTC's plan even without a BART extension from Colma to the San Francisco Airport. MTC's modeling system is conservative in estimating the impacts of density and increased transit service. It does not model the impacts of increasing pedestrian and bicycle friendliness in neighborhoods. Yet it shows substantial reductions in driving and pollutant emissions from increased density and improved transit services. Strongly applied nationwide, could such policies not only reduce, but reverse the growth of VMT/capita? What Can We Do? Be Practical That's fine, you might say, but what can we as air quality officials, industrial
leaders and ordinary citizens do? Consider the following list of practical actions,
including many suggestions from Urban Ecology.(19, 20) Conclusions Sprawl has resulted in increased auto ownership, driving and cold starts. Infill of traditional neighborhood developments into already built-up areas could reduce auto ownership, vehicle miles traveled and cold starts, reducing auto emissions. Citizens and public officials can take specific, incremental actions to promote this type of development. References Figure 1. Advantages of the RAFT Regional Transportation Plan over MTC's Plan.
Figure 2. Average Daily VMT/Hh vs Density, MTC's 1990 Household Travel Survey
Figure 3. Average Daily Vehicle Trips/Hh vs Density, MTC's 1990 Household Travel Survey
Figure 4. Average Daily VMT/Hh vs Density by Income Groups, MTC's 1990 Household Travel Survey
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