The study investigated the effect of an Electronic Toll Collection (ETC) system on reducing downwind air pollution under conditions with wind speeds greater than or equal to 0.5 m/s at the Sinyin toll station, located in Tainan, Taiwan. Specifically, the study examined the changes in traffic patterns, air pollution reductions, and the Excessive Lifetime Cancer Risks (ELCR) reduction before-and-after the implementation of the ETC system. Before data were collected from 12/27/2013 to 1/2/2014 and then After data were collected from 3/3/2015 to 3/9/2015.
At the study site, traffic data were collected with vehicle detectors. For emission monitoring, two sampling stations, one downwind and one upwind, were set up. The reference station was installed inside a van, and the instruments were powered by batteries. For the After study period, a scanning mobility particle sizer was utilized to measure the particle number concentration and size distribution of particles from 8 to 224 nm with a scan time of 150 s. Particles smaller than 100 nm were considered for UFP concentration. For PM2.5 measurement, a monitor with 60 s resolution time was used. The time intervals analyzed for both the traffic data and the air pollution monitoring data were during peak hours (7 AM to 9 AM and 4 PM to 6 PM). The ELCR from particle exposure was calculated using a formula from existing literature on the topic, as a function of PM2.5 and UFP inhalation slope factors, person’s body weight, and human daily inhalation rate.
The following benefits were found after the full implementation of ETC in the study area:
- The full implementation of ETC can help reduce UFP number concentrations and PM2.5 mass concentrations in the highway downwind area by 4000 #/cm3 and 20.5 μg/m3, respectively.
- The full implementation of the ETC can reduce PM2.5 mass concentration and UFP number concentration when challenged with similar traffic volumes.
- The average speed increased from 98.7 km/h to 101.4 km/ h (a 2.67 percent increase).
- An almost 50 percent reduction in ELCR was computed, mostly as a result of the reduction in UFP concentration rather than PM2.5.
The authors noted that the scope of the research was limited to one site in Taiwan. Additional studies would be needed to fully evaluate how different policy measures, such as ETC can help reduce the PM2.5 and UFP concentrations in near-highway environments.