Estimating Vehicular Emission Impact of Nighttime Construction with VISSIM and Different MOVES Emission Estimation Approaches

Shifting work zones from daytime to nighttime is a potential solution to air quality issues on roadway with high traffic volume and where it is undesirable to close lanes during peak hours. The expected benefit of such shifting is to reduce total fuel consumption and on-road vehicle emissions. However, the magnitude of emission reductions and air quality impacts has not been examined comprehensively at work zones. The study presented in this paper investigated the traffic-related emission impacts of work zones using an urban freeway case study. A VISSIM test bed combined with the Environmental Protection Agency’s MOVES emission model was used to estimate total emissions assuming daytime and nighttime lane-closure scenarios. Vehicle emissions were estimated using a link-based method and operating mode-based method. The results from both methods demonstrated that nighttime construction has a significant impact on both traffic speeds and vehicle emissions, primarily as a result of reductions in vehicle miles traveled. In addition, a horizontal comparison between the results from the two methods was made to assess the impact of different emission estimation approaches. The outcomes from the comparison highlight the potential importance of the operating mode-based approach for accurately estimate total traffic emission quantities when data or simulations are available.

Investigating the Impact of Meteorological Conditions on Near-Road Pollutant Dispersion between Daytime and Nighttime Periods

In urban areas in Texas and the rest of the United States, roadway work zone and construction activities are often conducted at night to reduce disruption to traffic and to prevent congestion caused by lane closures during peak hours. The reduced traffic delays due to nighttime construction have the potential to reduce traffic emissions. However, the air quality impacts associated with moving these activities from daytime to nighttime have not been studied in detail. Air quality impacts depend on two major factors: the traffic emissions and meteorological conditions. While the impact of traffic emissions between time periods has been studied in the literature, there is limited knowledge on understanding the impact of meteorological conditions on the dispersion of mobile source pollutants. This study specifically addresses this gap by evaluating the impact of the meteorological conditions on pollutant concentrations under different input settings related to the region, land use, distance from roadways, and averaging periods. The assessment of the impact of metrological conditions indicated that for the same amount of emissions, the nighttime period could result in higher pollutant concentration levels. However, given that traffic congestion and overall traffic volumes are generally substantially lower in the nighttime period, the findings do not imply that nighttime construction activities result in worse air quality in terms of pollutant concentrations. Thus, the relative difference in pollutant concentrations obtained from shifting construction activities from daytime to nighttime periods should be assessed based on a combination of meteorological and traffic conditions.