Transportation and Public Health: An Urbanist Conundrum

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Infographic designed by Betty Dabney.

Infographic designed by Betty Dabney.

Betty Dabney Author ImageMixed-use high-density infill of the inner city is now a high priority for the City of San Antonio.  The City Center Development Office and Centro Partnership have been working together to create a Downtown Strategic Framework Plan to implement the targets of SA2020 and create 7,500 new downtown housing units.

Stretching from Brackenridge Park on the north to I-10 on the south, and between Colorado and Mesquite Streets on the east-west axis, the areas to be redeveloped and their priorities are shown in this map:

Map of the Community Revitalization Action Group (CRAG) Area and the Center City Housing Incentive Program priorities. For more information, visit the Center City Development Office.

Map of the Community Revitalization Action Group (CRAG) Area and the Center City Housing Incentive Program priorities. For more information, visit the Center City Development Office.

Along with new residences, the redevelopment will attract new businesses.  This will bring more vitality to the inner city.  Indeed, such a viable inner city is necessary for San Antonio to be mature and thriving as a metropolis.  As the seventh largest city in the country, it certainly deserves to be a “grown-up” city in every respect.

Unless drastic measures are taken, however, this redevelopment will bring more traffic to the city’s center, with deterioration of the air quality and health of the people who live, work, shop and visit there. This is a complex issue which needs to be considered right along with the plans for new buildings.

If you are interested in this topic (and who wouldn’t be?), come to the Alamo Region Livability Summit tomorrow, Aug. 21, 8 a.m. – 4 p.m. at the American Institute of Architects office in The Pearl Brewery, 200 East Grayson, Suite 110.  Sponsored by the San Antonio/Bexar County Metropolitan Planning Organization, the conference is free, but please register in advance at or 210-227-8651.

San Antonio is already on the brink of non-compliance with the EPA’s Air Quality Standard for ground-level ozone, one of the components of smog.  Indeed, the past few days have been Ozone Action Days, where people with respiratory disease are discouraged from being outdoors and drivers are asked to avoid unnecessary trips, especially during the times of peak traffic.

Ozone is getting all the press, but vehicular exhaust, so-called mobile sources, also produces other components which could be cause for concern from the standpoint of health.   Here is a short list of them:

Major Air Pollutants from Vehicular Exhaust 

  • Heavy metals:  Chromium, mercury, nickel, manganese, lead
  • NOx:  Oxides of nitrogen. A mixture of nitrogen dioxide (N02) and nitric oxide (NO) formed from air when burning fuel. Regulated by the EPA.
  • O3:  Ground level ozone, formed from VOCs, NOx, heat, and light. Regulated. Is a highly reactive oxidizer.
  • PAHs:  Polynuclear aromatic hydrocarbons. Benzo[a]pyrene, for example, causes cancer.
  • PM:  Particulate matter (PM2.5, PM10). Regulated. Small ultrafines ( <100 nm) can enter the body directly.
  • S02:  Sulfur dioxide, formed from combustion of fossil fuels. Regulated by the EPA, forms acid with water.
  • VOCs:  Volatile organic compounds, released in unburned fuel. Not regulated, but some are monitored.
  • Smog:  All of the above

Here’s why ozone is a problem.  It causes difficulty in breathing and has been linked with serious health problems, including asthma and other chronic respiratory diseases. High levels also damage vegetation – think of all those plants that have recently been replaced along the Mission Reach after the flood.

Ozone is not emitted directly, it is formed from the reaction of VOCs and N02 with sunlight and heat. Ozone tends to localize over the areas of heaviest traffic.  Ozone and smog are higher during the rush hours and in the warmer months. The high proportion of pavement in urban centers produces an urban heat island effect, where temperatures may be more than seven degrees warmer than in the surrounding suburban and rural areas.  On top of that, global climate change is happening even faster than scientists previously thought, making the urban heat island effect and air pollution even worse.

We are concerned about air pollutants not only because of regulatory compliance, but also because they have been linked with many diseases and adverse reproductive outcomes as well as premature death (see schematic below).

Infographic designed by Betty Dabney.

Infographic designed by Betty Dabney.

Poor air quality could thwart the plans for downtown re-development.  If air quality deteriorates, people may be discouraged from moving in – some may even move away.  Even the tourism industry may suffer.

There are many interacting factors to consider.  Public transportation may either improve or worsen the air quality, depending on the age and emissions of the fleet, the level of ridership, and whether or not the riders have given up their private vehicles. VIA is moving to a cleaner and greener fleet, but there are still many older buses on the streets. Hence whether or not increased public transportation will make the air cleaner or dirtier is an open question.  (You can read about my experiences riding the bus in a previous Rivard Report story.)

People who use public transportation tend to walk more than those who don’t and may even lose weight.  In one study from researchers at the University of Pennsylvania, light-rail commuters lost up to six pounds (MacDonald et al, 2010).  But serious air pollution can offset the health benefits of exercising according to a 2011 study.  Severe heat and air pollution may discourage people from walking and might lead to more vehicles on the road, thus exacerbating the pollution even more.  Downtown is a perceived high-crime area, and people may also be reluctant to walk where there is a perception of danger.

Inter-Dependent Factors in Inner City Redevelopment

These are some, but probably not all, of the factors that would figure into the effects of redevelopment on air quality and health. This is a very complex scenario because these factors affect and are affected by the others (in technical lingo they can be both independent and dependent variables). The inter-relationships are shown below:

Courtesy of Betty Dabney.

KEY: “+” = Expected to increase. “–” = Expected to decrease. Courtesy of Betty Dabney.

If the central city revitalization is to succeed, it will depend on reducing vehicular emissions. This can be accomplished by very high ridership on public transportation and by severely limiting private and commercial vehicles.

Difficult policy decisions will need to be made.  At a minimum, downtown residents and commuters could be incentivized not to drive their cars every day. Limiting the number of parking spaces, more remote park-and-ride lots, limiting commercial deliveries to night-time, and pedestrianizing some streets should be considered.  Considerable political courage will be needed in the face of almost certain objections to any proposed changes. Pedestrianized streets, or “complete streets,” with open-air markets, sidewalk cafes, and small shops are appealing and could therefore extend the life of downtown – for tourists and residents – beyond the River Walk and Alamo Plaza.

In any case, the success of the central city depends on its air quality, and the time for thoughtful action is now.

Research and Suggested Reading:

“Air Pollution and Health” by Bert Brunekreef and Stephen T Holgate (2002).

“Exercise and outdoor ambient air pollution,”  by A.J. Carlisle and N.C.C. Sharp in the British Journal of Sports Medicine.

“Health Impacts of the Built Environment: Within-Urban Variability in Physical Inactivity, Air Pollution, and Ischemic Heart Disease Mortality” in Environmental Health Perspectives.

Traffic-Related Air Pollution: A Critical Review of the Literature on Emissions, Exposure, and Health Effects in the Health Effects Institute (2009).

Low-level exposure to air pollution and risk of adverse birth outcomes in Hillsborough County, Florida.


Betty Dabney, PhD is an Adjunct Associate Professor in UTSA’s College of Architecture Center for Urban and Regional Planning Research.  She retired from the faculties of Texas A&M’s School of Rural Public Health and the University of Maryland School of Public Health, where she was the founding head of the environmental health program.  She has also worked for the Maryland Department of the Environment, for Fortune 50 companies, and has been an independent consultant in environmental health.  She was on the Maryland Governor’s Commission for Environmental Justice and Sustainable Communities. In her spare time she is a fine-art photographer:


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