Measuring the Social Net Benefits of COVID-19 Restrictions: The Case of Reduced Vehicle Use in a Pollution-Prone Region of Utah

A number of natural experiments have recently found that COVID-19 restrictions imposed in nations worldwide are correlated with short-term reductions—in some cases dramatic reductions—in mobile-source air pollu-tants. Noticeably absent from these studies are estimates of the social net benefits associated with the changes in human behavior underlying the pan-demic-induced effects. Using readily available data provided by the state of Utah and the U.S. Environmental Protection Agency’s Co-Benefits Risk Assessment Health Impacts Screening and Mapping Tool (COBRA), we find that daily social net benefit was positive during a pandemic-induced shutdown from March to April, 2020 in Utah’s Wasatch Front region solely when COBRA’s “high” health benefit estimate from combined reductions in PM 2.5 and NO x concentrations are weighed against the region’s “low” vehicle-trip cost estimate. All other scenarios correspond with negative net benefit estimates, i.e., when high and low benefit estimates of reductions solely in PM 2.5 concentrations as well as for combined reductions in PM 2.5 and NO x concentrations are weighed against the region’s high vehicle-trip cost estimate. Generally speaking, social net benefits are higher for two of the Wasatch Front’s four counties.

Ground-level ozone concentrations were also not found to have changed significantly in the short term. Overall, a positive correlation was found between more daily confirmed COVID-19 cases and improvements in air quality. See [5] [6] [7] for additional findings from China. Similar results are found for India by [8]. Metropolitan areas nationwide experienced significant reductions in NO 2 and PM 2.5 concentrations during the lockdown period. Coarse particulate matter (PM 10 ), and ground-level ozone concentrations also showed substantial reductions, whereas CO concentrations exhibited a moderate decline. Similar to [4], SO 2 concentration levels did not show any defined reduction trends and increased in the cities of Mumbai, Bengaluru, and Kolkata. Similar reductions in PM 2.5 , CO, and NO 2 concentration levels in Pittsburgh, Pennsylvania are found by [9] as a consequence of COVID-19 related closures, particularly at otherwise high-traffic sites during rush hours. However, the authors found no significant change in industry-related intraday variability of CO and PM 2.5 concentration levels in response to the enactment of COVID-19 control measures.
Noticeably absent from these studies are estimates of the social net benefits associated with the changes in human behavior underlying the pandemic-induced effects (notwithstanding [11], which develops an interesting empirical approach to measure public health benefits associated with reductions in cumulative confirmed COVID-19 (CCC) cases using total capitalization of 14 stock market indices for large-cap stocks, as well as an estimated elasticity of CCC cases obtained from a panel-data analysis of daily observations from the third week of January to the first week of April, 2020 information about each county is provided in the next section).
Our results, therefore, suggest that the mitigatory effects of COVID-19 restrictions on metropolitan-area pollution levels reported by [4] [8] [9] and [10] should be interpreted with a degree of caution. While obviously worth heralding, the pandemic-induced reductions in air pollution levels estimated in these studies may nevertheless fail to pass social cost-benefit tests when the economic costs of what was foregone to achieve the reductions are accounted for.
The next section provides a brief description of Utah's Wasatch Front region, a region prone to episodic elevations in PM 2.5 concentration levels during the winter months and therefore amenable to natural experiments associated with any short-term environmental shocks that might lead to sudden changes in these levels. Section 3 presents our estimates of the impacts of the region's COVID-19 restrictions on its vehicle usage, PM 2.5 concentrations, and associated public health outcomes. These impacts are captured by highly aggregated, secondary sources of data. Section 4 describes our COBRA estimates of the health benefits associated with the regional reductions in concentrations, as well as the corresponding cost estimates of foregone vehicle trips. Together, these estimates enable us to derive an array of social net benefit measures. Section 5 summarizes our findings and expounds upon the advantages of our method, but also reminds the reader of the method's key limitation.

Utah's Wasatch Front
The Wasatch Front is a sprawling metropolitan region located in north-central Utah (see Figure 1). and accounts for almost 90 percent of the state's gross state product [12]. The Wasatch Front has experienced considerable growth since the 1950s-its population increasing by over 300% to its current 2.5 million residents, with projections of the population reaching six million residents by 2065 [13]. Much of the remaining undeveloped land is rapidly being developed, forcing local governments and regional authorities to contend with problems of urban sprawl and related transportation issues. According to [13]'s projections, just under 30% of Utah's population will reside in Utah County by 2065, as will 40% of new residents to the state during this 50-year time span. Just over 20% of new residents will reside in Salt Lake County, currently the Wasatch Front's most populous county. Forty and roughly 25% of those employed in the state are projected to be working in Salt Lake and Utah Counties, respectively, by 2065. Davis County is projected to experience the state's third highest employment growth rate during this same time frame.
The Wasatch Front is emblematic of a fast-growing metropolitan area known for its abundance of quality-of-life attributes, such as convenient access to outdoor recreation, ample job opportunities, and pockets of progressive urban growth [14] [15]. But as [16] points out, over the past two decades the region has been plagued by persistently poor air quality, particularly during the winter months when episodic temperature inversions entrap vehicle emissions, in turn elevating the region's PM 2.5 concentrations ( [17] estimates that roughly 60% of PM 2.5 concentrations in the Wasatch Front region are attributable to mobile-source emissions). The problem is severe-the Wasatch Front has been repeatedly ranked by the American Lung Association (ALA) as one of the nation's ten worst metropolitan areas for short-term particulate concentrations [18].
The region's residents have expressed a strong desire for improvements in environmental-protection and resource-management policies that have not kept pace with the region's development over time. According to [19], Wasatch Front residents believe that mitigation of poor air quality should be the state's second-highest priority, tied with funding of public education and only slightly behind management of water resources. Survey results indicate that, inter alia, over 60 percent of respondents believe air quality negatively impacts their lives, over 90 percent believe good air quality is integral in maintaining good health, and almost 80 percent believe air quality has worsened in the Greater Wasatch and Northern Utah regions over the past 20 years. Further, residents identify changes in how they transport themselves (i.e., changes in the extent to which they contribute mobile-source emissions), e.g., telecommuting, ridesharing, use of public transit, reduced idling and unnecessary driving, as being the most beneficial approaches to improving air quality.
As discussed in [16], the state of Utah and various Wasatch Front regional authorities have not been completely idle in addressing the issue of episodic air pollution outbreaks, or what is commonly known as the occurrence of "red air days" during the winter months. Indeed, several lines of action have emerged  [20]. Further, emissions testing programs require tests every two years on all vehicles registered in the Wasatch Front region with model years less than six years old, unless the model year is 1967 or older [21]. Further, the state actively promotes changes in transportation behavior, e.g., carpooling, use of public transit, teleworking, trip chaining, alternative work schedules, etc., through its Travelwise program [22]. In conjunction with statewide efforts to address the problem, several non-profit organizations advocate and educate for greater awareness of the problem, e.g., Utah Physicians for a Healthy Environment, Breathe Utah, and Heal Utah. Despite these concerted efforts on the part of governmental agencies and non-profit organizations, the Wasatch Front's red-air-day problem has stubbornly persisted.

COVID-19's Impacts on Vehicle Use, PM2.5 Concentrations, and Public Health Outcomes in Utah's Wasatch Front Region
On March 6, 2020, Utah Governor Gary Herbert declared a state of emergency and enacted a statewide "Stay Safe, Stay Home" policy in response to a surge in the state's COVID-19 infection rate. Ten days later, Salt Lake County issued a public health order closing many business and places of mass gathering. According to [23], these actions by state and regional authorities resulted a rapid decrease in emissions from vehicle traffic, which in turn noticeably improved the To illustrate these differences in concentration levels, [23] provide satellite  The distinction between the table's high and low estimates is based solely upon the sensitivity of COBRA's estimates for mortality and nonfatal heart attacks. Sensitivities of the other categories comprising COBRA's overall public health estimates associated with reductions in PM 2.5 , NO, and NO 2 concentrations-pertaining to infant mortality, hospital admissions for upper and lower respiratory ailments, asthma, chronic lung disease, and nonfatal cardiovascular conditions, acute bronchitis, asthma exacerbation, emergency room visits, minor restricted activity days, and work loss days-do not exhibit such sensitivity and are therefore not adjusted in the determination of high versus low aggregate public health benefits. High estimates are roughly double the low estimates for each county, and thus for the Wasatch Front as a whole.
It is interesting to note that the differences inpublic health benefits across counties do not track corresponding differences in population sizes. For example, although Salt Lake County's population size of over 1.16 million is by far the Wasatch Front's largest, in turn corresponding to the region's highest estimates of dailypublic health benefits associated with a reduction in PM 2.5 concentrations (low estimate of roughly $85,000 and high estimate of over $191,000), the county with the next highest population size-Utah County, with a population of just over 670,000-records the lowest daily benefits of the four Wasatch Front Counties from reductions in PM 2.5 concentrations (COBRA reports annualized benefit estimates, which we have converted to their daily equivalents. Population estimates are taken from [24]). Davis County's population size of just under 360,000 (the region's third lowest) corresponds to the region's second-highest estimated benefits from reductions in PM 2.5 concentrations (low estimate of just over $24,000, high estimate of almost $55,000).
These differences result from differences in the demographic compositions of the four counties. However, others believe that both NO and NO 2 should be considered NO x [27].
As anticipated, both the low and high estimates in Table 1 Table 2 are larger than the estimated PM 2.5 elasticity of 1.00 reported in [29] for Cache County, Utah, we discuss the implications of constraining our PM 2.5  Lastly in Table 2, we apply both "low" and "high" estimates of the per-trip benefit associated with a vehicle trip to the estimated reductions in county-wide vehicle trips in order to derive estimates of the average, daily, county-wide costs of the decreases in vehicle trips that occurred in the Wasatch Front in response to the COVID- 19  To determine the county-wide reductions in vehicle trips, we extracted daily trip-count data from [28] for the months of March-April, 2019 and March-April, 2020 from two randomly selected automatic traffic recording stations (ATRs) in Salt Lake County and one ATR each in Davis, Utah, and Weber Counties. Each station is located on the main interstate highway (I-15) that runs through the heart of the Wasatch Front. The ATRs were chosen near relatively large cities in each county. The five ATRs were also chosen such that the total number of average daily vehicle trips recorded for March-April, 2019 was roughly equal to the Federal Highway Administration's (FHA's) estimated total for the Wasatch Front's I-15 corridor in 2019 of over 314,000. In this way, we effectively calibrated our choice of ATRs to the FHA's 2019 average daily vehicle-trip estimate for the Wasatch Front [34].
Choice of which ATRs to include in the estimation of county-wide trip counts is admittedly a challenge. Including too many ATRs risks double-counting trips made by a certain percentage of the same vehicles. Including too few risks under-counting the number of trips taken overall. It is precisely because of these concerns that we calibrated our choice of ATRs to the FHA's 2019 average daily vehicle-trip estimate for the Wasatch Front. By doing so, we ensure a more realistic baseline from which to compare the reductions in vehicle trips that occurred in 2020 in response to the region's COVID-19 public health order.

Social Net Benefit Estimates
Based upon the information contained in Table 1 and Table 2 in Section 3, we  Table 3. We see that daily social net benefit is positive for the region as a whole solely when COBRA's high daily public health benefit of $723,000 from reduced PM 2.5 and NO x concentrations (see Table 1) are weighed against the region's low vehicle-trip cost estimate of $330,544 (see Table 2 Substituting [29]'s PM 2.5 elasticity value of 1.00 for the value 1.68 from Table   2, and then reducing the NO x elasticity estimate in Table 2  The pattern of social net benefits displayed in Table 3 is not uniform across the different counties. For example, Appendix Table A1 shows that the daily social net benefit estimates for Salt Lake County follow the same pattern as Utah County's in Table 4. However, Weber County's pattern in Appendix Table A2 resembles that for the Wasatch Front as a whole in Table 3.   Our results, therefore, suggest that the mitigatory effects of COVID-19 restrictions on metropolitan-area pollution levels reported in several previous studies should be interpreted with a degree of caution. While obviously worth heralding, the pandemic-induced reductions in air pollution levels estimated in these studies may nevertheless fail to pass social cost-benefit tests when the economic costs of what was foregone to achieve the reductions are accounted for.

Summary and Conclusions
The method we have used here to estimate the social net benefits associated with a short-term shock to society, such as the imposition of COVID-19 restrictions, demonstrates how limited, secondary data on changes in human behavior can be leveraged to more fully assess the extent to which the shock has altered economic outcomes. Here, "limited" refers to the availability of only highly aggregated data, such as, in our case, year-on-year, region-wide vehicle trip data and similarly aggregated pollution concentration data. When the shock in question pertains to environmental health, e.g., the effects of elevated pollution concentrations on a given population, a tool designed to convert changed concentration levels into corresponding damage estimates, such as COBRA, is necessary. This