Air Quality, Built and Natural Environment

Houston, TX
United States

Air Alliance Houston is concerned about the health effects of a proposed freeway expansion on children attending schools within traffic-related air pollution (TRAP) zones. To investigate these effects, Air Alliance Houston used the 500 Cities data to conduct a health impact assessment (HIA) of the proposed I-45 highway expansion project, known as the North Houston Highway Improvement Project (NHHIP). The team used the data to quantify the project’s potential positive and negative health effects for inclusion in the final environmental impact statement. This project represents a model for integrating health impact assessments into future mobility projects in the Houston metropolitan area and for raising public awareness of the public health implications of freeways.



Air Alliance Houston is concerned about the health effects of the proposed I-45 expansion project that will cover roughly 24 linear miles of freeway in Houston, running from the I-45 North/Beltway 8 intersection on Houston's north side to the I-45/I-69/State Highway 288 intersection just south of Midtown.

Air Alliance Houston believes that this proposed highway expansion could specifically impact the health of the roughly 80,000 Houston-area children attending schools within TRAP zones adjacent to the freeway. Research has shown that children living or attending schools near highly congested freeways like I-45 are at greater risk of exposure to air pollutants, and exposure at such an early age can lead to long-term health and/or developmental implications. Furthermore, several traffic-related air pollutants—such as diesel particulate matter, benzene, 1,3-butadiene, and formaldehyde—are known to cause cancer, adding additional cause for concern.

To determine the potential effects of this highway expansion on health outcomes of children, Air Alliance conducted a health impact assessment to establish the ways in which this proposed policy could benefit and/or harm community health. This HIA has the following three main goals:

  • Quantify the project’s potential co-benefits and co-harms to health for inclusion in the final environmental impact statement.
  • Serve as a model project to integrate HIAs into future mobility projects in the Houston metropolitan area.
  • Raise public awareness of the public health implications of freeways.

Focusing on nine schools located within 150 meters (500 feet) of the NHHIP project, the HIA is using a combination of 500 Cities data, external data sets, community data gathering, literature reviews, and stakeholder input to assess the potential positive and negative health effects associated with the following:

  • the proposed freeway expansion
  • proposed mitigation strategies

First, the team selected seven key 500 Cities health outcomes to consider in their analysis, identifying the following indicators as most relevant to their approach: asthma, cancer, coronary heart disease, chronic obstructive pulmonary disease, obesity, physical health, and mental health. They looked at these health outcomes in relation to the nine identified schools and considered relevant trends.

 Air Alliance Houston combined these 500 health outcomes data with external data, consolidating a local health database of more than 70 social, environmental, and health data as well as several campus-level indicators on the census-tract level. The team pulled together data from the US Census, Center for Disease Control, National Air Toxics Assessment, Harris County Flood Control District, and Harris County Appraisal District (among other data points) to paint a larger narrative about health and health outcomes in the region.

To further inform their assessment, the Air Alliance team collected local data through questionnaires that asked school administrators about their campus air quality, collecting data on key indicators like how many cars idle near campus at pick-up and drop-off, how long students spend outdoors, and how safe students feel traveling near the highway.

The team gave presentations at local stakeholder convenings to gather additional feedback and insight from different players in the community on their project approach. The team summarized their findings in community workshop reports that outline community member feedback regarding where they currently experience negative health outcomes and what changes they would want to be made.

The team also created NHHIP one-pagers and infographics for a variety of stakeholder audiences (e.g., residents, elected officials), using the 500 Cities data to form the basis for comments related to neighborhood health status and set the geographical extent for comparisons between individual neighborhoods and the city.

After conducting a rigorous analysis on the multiple levels of data gathered and collected, Air Alliance Houston synthesized their findings into the NHHIP Health Impact Assessment. Within the HIA, the team outlined community impacts and possible solutions that the Texas Department of Transportation, school systems, and other local actors could engage in to address health concerns including student health, environmental justice, and community safety.

In addition to the health impact assessment, Air Alliance Houston was able to use a powerful scenario-planning tool to perform a comprehensive National Public Health Assessment Module assessment on one to two school campuses along the NHHIP corridor. This tool combines environmental data from the US Environmental Protection Agency with a health outcome database of 40,000 individual health records to model the effects of changes in the environment on physical activity, obesity, mental health, general health status, and chronic disease. A second level of analysis is also available to predict health care costs associated with changes to prevalence of chronic disease and health outcomes related to increased exposure to air pollution.


By offering health data at the census-tract level, Air Alliance Houston knows the 500 Cities dataset significantly informed the baseline health conditions of the census tracts adjacent to the project, and that it played a critical role in the subsequent identification of mitigation strategies to address the adverse health impacts identified. From their experience working with the Houston tract-level data, Air Alliance Houston also saw that the adverse health conditions identified in the 500 Cities data often correlate with socioeconomic characteristics and disparities in the urban built environment, which might be a relevant topic for future study.

Air Alliance Houston plans to continue using the 500 Cities Data in several ways. The team has already incorporated the 500 Cities Data into other datasets that display the correlation between adverse health conditions and environmental hazards in their region. Air Alliance Houston believes that the 500 Cities Data helps stakeholders better understand the spatial relationships between community and health at a scale that provides more granular detail than county-level data. The team also thinks the 500 Cities data helps to frame conversations with stakeholders to discuss health inequities. Air Alliance Houston anticipates using the data to help inform planning for future grant opportunities and continuing to introduce the 500 Cities dataset to other researchers at conferences looking for health data at the census-tract level for use on their projects.


Air Alliance Houston has identified a few recommendations for organizations interested in pursuing similar projects centering in the 500 Cities data, outlined below:

  • Community engagement requires a high level of commitment from the project team, as it is a resource-intensive endeavor.  We found that we were able to spark community interest in the freeway expansion by sharing data with them, starting with the 500 Cities dataset and extending out to other publicly available data. However, once we activated the community, we were obliged to follow up and respond to their concerns. As we did not have a dedicated community outreach staff member to support the HIA, the project team that was working on other aspects of the project (e.g., compiling data, performing the assessment, writing the report, developing communications materials) were also responsible for maintaining community engagement. In other words, it takes a collaborative effort and dedicated resources to ensure communities are engaged throughout the HIA.
  • Working with a coalition can broaden impact and engage a variety of key stakeholders. The HIA was done within the context of a broader coalition of organizations that had already been working to engage decisionmakers to voice concerns about the planned expansion (i.e., the Make I-45 Better Coalition). Therefore, the HIA became integral to the broader coalition and community outreach about the project. We were able to integrate the assessment and its findings into the coalition’s communications and engagements with elected officials and decisionmakers. 
  • If you are planning on collecting primary data, it is important to account for certain expected and unexpected delays. A unique aspect of our project was collecting real-time air quality data using two approaches. The first lesson learned was that placing air-monitoring equipment at schools requires going through a school district’s protocol and staff at the campus level to get the monitor placed at the appropriate location. This takes time and persistence. Campus staff are busy educating and caring for children on their campus. Our staff had to reach out multiple times via email and phone and visit the campuses to eventually get the air monitors placed. In the end, we were not able to install air monitors at all of the campuses we included in the HIA. 
  • It is key to ensure that you are well-suited for primary data collection with appropriate equipment and a good understanding of relevant literature. We also conducted mobile air monitoring. It is important to understand what air-monitoring equipment is needed ahead of time to ensure that it is available once the project starts. We had issues obtaining the monitoring equipment needed to measure NOx emissions. As a result, our mobile-air-monitoring timeline was pushed back on multiple occasions. Based on a review of the literature that indicated that levels of particulate matter fluctuate between summer and winter, our original mobile-air-monitoring protocol included one week of monitoring in August and another week of monitoring in January. However, owing to the delays in obtaining the right equipment, we were only able to monitor in January/February. This is a weakness in our mobile-air-monitoring results.
  • Collecting qualitative data is essential to provide tailored recommendations for each area of focus. We developed a school questionnaire and held several community meetings to be able to incorporate campus-specific information into the assessment and develop tailored recommendations for each school. Although obtaining information from schools and communities is challenging because of their busy schedules, the qualitative information proved highly insightful and filled holes in the publicly available data, providing valuable insight into the day-to-day operations of these schools and the lived experiences of the adjacent communities. This information was crucial for personalizing the assessment's results and recommendations.
  • Spend enough time selecting the indicators and datasets that will be most relevant to your analysis. Developing the indicators to conduct the assessment and producing maps of key information took much more time than we anticipated in our original proposal. This involved locating and manipulating a variety of public data sources to conform with the uniform tract-level scale of the project, as well as developing an approach to visually display a variety of information on maps. Though the 500 Cities data underpinned the project in terms of neighborhood health status, its focus on adult populations was a limitation for our project, because the HIA highlights the impact of the freeway expansion on K-12 schools. Expanding the 500 Cities dataset to include children would greatly benefit projects like ours that focus on children and schools.
  • Clearly outline the intended use, impact, and scope of the health impact assessment in stakeholder and community meetings. One of the consistent pieces of feedback we received from the community-meeting evaluations is that some community members left still not understanding why we were conducting the health impact assessment and how it related to the I-45 expansion. This could mean that there was a disconnect in how we were presenting the information. Developing language to discuss HIAs, similar to what has been done for the social determinants of health, might help advance understanding about the benefits of conducting HIAs on transportation projects and policies more broadly—particularly when the HIA is focused on a nonhealth sector. Another issue to consider is the scope of the project that the resources available for conducting the HIA make feasible. Some residents expressed disappointment about the fact that we had limited the HIA to campuses rather than communities more broadly. However, the scope was limited because of the timeline and resources available. In other words, it is important to be mindful of and prepared for how a variety of stakeholders will interpret the scope of the HIA if they were not involved in the scoping phase of the project.

To learn more about Air Alliance’s work, follow @airallianceHOU on Twitter. If you are interested in learning more about this team’s project approach or have specific questions regarding replicating their work in your community, please feel free to contact the Principal Investigator of this project, Bakeyah Nelson.