Green infrastructure and electrostatic precipitators may provide a sturdy line of defence against air pollution, but, as the previous two entries have demonstrated, they are by no means perfect solutions. This got me thinking – if it’s impossible to clean up air pollution entirely, why don’t we start at the root of the problem and reduce the need for cleaning? Afterall, prevention is better than cure!
According to Baghestani et al. (2021), cordon pricing (congestion charge) is a form of traffic control that serves to ameliorate both traffic congestion and environmental pollution. Cordon pricing works through imposing a toll on vehicles that cross the cordon boundary during the specified time range. Thus, the theoretical rationale behind cordon pricing is to deter or reduce private commute, thereby limiting the vehicular emission of air pollutants.
To understand the effects of cordon pricing in Manhattan County, the authors compared models of hypothetical “low” and “high” charging schemes against the existing “base scenario”. The promising results suggest that implementing cordon pricing could cause exposure to PM2.5 to potentially fall between 7% to 13% for the general population, and 22% to 28% for those working in the CBD that is typically characterised by denser traffic. In particular, they attributed the lower PM2.5 exposure to greater use of public transport, decline in vehicle miles travelled, and higher average travel speed.
Figure 1. Projected impacts of cordon pricing on PM2.5 concentration in Manhattan County (Baghestani et al., 2021)
Figure 2. Projected (a) absolute and (b) percent change in average daily PM2.5 concentration in Manhattan County due to cordon pricing (Baghestani et al., 2021)
Keivabu and Rüttenauer (2022) observe similar results that provide further testament to the benefit of congestion charges. Beyond the flat fee of 5£ imposed for entering the Congestion Charge Zone (CCZ) in London, the study encompassed the effects of tighter traffic regulations from September 2015 onwards that “explicitly targeted a reduction in hazardous pollution from traffic” instead of simply controlling traffic volume. Not only did the concentrations of multiple pollutants fall significantly within the CCZ, the same benefits extended far beyond the CCZ’s perimeter, albeit at a lower magnitude. Hence, these findings illustrate the vast potential of congestion charges (or cordon pricing) when complemented by supplementary measures that further curb emissions right at the source.
Figure 3. Change in pollution within and outside the CCZ after the tightening of CCZ regulations in September 2015 (Keivabu and Rüttenauer, 2022)
Nonetheless, as in the case of green infrastructure and electrostatic precipitators, the application of congestion charges or cordon pricing is not entirely free of controversy. Green et al. (2020) found that the London CCZ, though successful in reducing the concentration of most pollutants, led to a huge increase (14% to 17%) in NO2 concentrations. Ironically, in the planners’ bid to encourage more commuters to switch towards public buses, the exemption of these diesel vehicles from CCZ fees manifested in greater emissions of NO2 from these very vehicles touted as being “environmentally-friendly”.
Despite this flaw in London’s CCZ that was exposed by Green et al. (2020), I am inclined to believe that the congestion charge / cordon pricing traffic control system is one that brings about net environmental benefit. However, it is imperative that planners do not rest on their laurels and instead work towards devising innovative solutions that will circumvent this flaw or further enhance the efficiency of such a system. The introduction of “cleaner” public transport vehicles and raising of diesel cars’ standards to enter the CCZ (Keivabu and Rüttenauer, 2022) is an excellent case in point that should serve as an example for cities across the world. Finally, implementing something like the CCZ may entail trade-offs with public satisfaction and requires substantial financial capital to fund high-class transportation networks and infrastructure. Hence, the intersection of environmental needs with political stability and economic conditions poses yet another complex challenge that will demand planners to act without compromising performance elsewhere.
Until the next entry, breathe safe and be safe!
References
Baghestani, A., Tayarani, M., Allahviranloo, M., & Gao, H. O. (2021). Cordon pricing, daily activity pattern, and exposure to traffic-related air pollution: A case study of new york city. Atmosphere, 12(11), 1458. https://doi.org/10.3390/atmos12111458
Conte Keivabu, R., & Rüttenauer, T. (2022). London congestion charge: The impact on air pollution and school attendance by socioeconomic status. Population and Environment, 43(4), 576–596. https://doi.org/10.1007/s11111-022-00401-4
Green, C. P., Heywood, J. S., & Navarro Paniagua, M. (2020). Did the London congestion charge reduce pollution? Regional Science and Urban Economics, 84, 103573. https://doi.org/10.1016/j.regsciurbeco.2020.103573