One key argument in favor of removing stoplights on Route 9 in Middletown is that it would reduce emissions in Middletown. Those who advance this theory argue that idling cars waiting at the stoplights use fuel and thus emit carbon dioxide and other pollutants into the air in Middletown. If those cars were able to drive straight through, they argue, they would emit less.
It is undoubtedly the case that idling cars emit more polluting exhaust than cars driving a consistent speed. Accordingly, measures to facilitate traffic flow tend to decrease emissions in the short run.1 In the long run, however, facilitating traffic flow invites more traffic. The logic goes like this: if traffic lights were removed on Route 9, travel times on the stretch of highway would certainly decrease initially, and cars would more often travel at a consistent speed and thus emit less. Over time, however, people would recognize that the highway was moving faster, and more people would choose to drive there. This phenomenon is known as induced demand, and it means that when traffic capacity is expanded, the road in question nearly always ends up with the same level of congestion that it had prior to the expansion–if not higher–because of increased vehicle volume. Induced demand has been documented in many academic studies2,3,4 as well as in various other cases comparable to Middletown.5
A lack of reliable long-term congestion relief also means a lack of reliable long-term emissions relief. In fact, a study looking specifically at traffic flow-enhancing measures that, similar to stoplight removal, ostensibly improve traffic and thus reduce emissions found that increased vehicle traffic “quickly diminish[es] any initial emission reduction benefits” from traffic flow management.6 In that study, vehicle volume would not even need to reach original congestion levels in order to result in higher emissions than prior to traffic flow enhancement. That study built on a prior study that similarly found that enhancing traffic flow does not lead to long-term emissions reductions because of the overall increase in vehicles.1
It is impossible to know for sure whether Middletown would follow this pattern. The Connecticut Department of Transportation lists reducing congestion as a key motivation for the proposal of removing stoplights, implying that the DoT believes that traffic will be eased. Whether reductions in congestion are sustainable, however, seems a more open question.
Key also is the role of electric and zero-emission vehicles, which are growing as a share of the vehicles on the road in the U.S. Indeed, the prior study concluding that traffic flow enhancement actually increases long run emissions noted that the cleaner the vehicles on the road, the less beneficial the initial emissions reduction is at all. It also found, unsurprisingly, that the long term increases in emissions were similarly lowered, given the lower emissions from increased vehicle traffic. But it’s worth noting that vehicle emissions don’t just come from the exhaust pipe; electric vehicles can’t solve particulate matter emissions from tire matter and road wear, among other sources.7 In fact, because of their relatively higher weight, electric vehicles actually increase these sources of emissions, potentially offsetting reduced exhaust emissions.8 To be clear, electrifying vehicular transport is still a worthy pursuit. But efforts to reduce air pollution in cities like Middletown should be focused on reducing the number of cars more than changing the cars themselves.
In short, removing stoplights on Route 9 is likely in the short term to reduce congestion and, as a result, emissions and pollution. That reduction, however, may be short-lived. Within a few years, vehicle volume may well have increased enough to actually worsen Route 9’s impact on Middletown’s air quality.
References
1Stathopoulos, Fotis G., and Robert B. Noland. “Induced Travel and Emissions from Traffic Flow Improvement Projects.” Transportation Research Record: Journal of the Transportation Research Board 1842, no. 1 (January 2003): 57–63. https://doi.org/10.3141/1842-07.
2Duranton, Gilles, and Matthew Turner. “The Fundamental Law of Road Congestion: Evidence from US Cities.” Cambridge, MA: National Bureau of Economic Research, September 2009. https://doi.org/10.3386/w15376.
3Hansen, Mark, and Yuanlin Huang. “Road Supply and Traffic in California Urban Areas.” Transportation Research Part A: Policy and Practice 31, no. 3 (May 1997): 205–18. https://doi.org/10.1016/S0965-8564(96)00019-5.
4Noland, Robert B., and William A. Cowart. “Analysis of Metropolitan Highway Capacity and the Growth in Vehicle Miles of Travel.” Transportation 27, no. 4 (2000): 363–90. https://doi.org/10.1023/A:1005288826997.
5Mann, Adam. “What’s Up With That: Building Bigger Roads Actually Makes Traffic Worse.” Wired. Accessed November 19, 2023. https://www.wired.com/2014/06/wuwt-traffic-induced-demand/.
6Noland, Robert B., and Mohammed A. Quddus. “Flow Improvements and Vehicle Emissions: Effects of Trip Generation and Emission Control Technology.” Transportation Research Part D: Transport and Environment 11, no. 1 (January 2006): 1–14. https://doi.org/10.1016/j.trd.2005.06.003.
7Liu, Ye, Haibo Chen, Ying Li, Jianbing Gao, Kaushali Dave, Junyan Chen, Tiezhu Li, and Ran Tu. “Exhaust and Non-Exhaust Emissions from Conventional and Electric Vehicles: A Comparison of Monetary Impact Values.” Journal of Cleaner Production 331 (January 2022): 129965. https://doi.org/10.1016/j.jclepro.2021.129965.
8Timmers, Victor R.J.H., and Peter A.J. Achten. “Non-Exhaust PM Emissions from Electric Vehicles.” Atmospheric Environment 134 (June 2016): 10–17. https://doi.org/10.1016/j.atmosenv.2016.03.017.
