Traffic scenarios on Sadr Overpass: A multi-criteria analysis considering air pollution

Traffic management in cities necessitates the implementation of comprehensive strategies and correct scheduling of demand management in order to reach sustainable development goals. Transportation is the main contributor to urban air pollution imposing high cost to communities. Emission from mobile sources in Tehran is responsible for 85 percent of the total air pollutant emissions. Therefore, assessment of emission rates in different districts may be used as the base for air quality management decisions. Due to the complexity of effective policies that lead to environmental sustainability for reducing the emissions of air pollutants caused by transportation using Multi Criteria Decision Making (MCDM) approaches could be an effective and the most appropriate approach.
 Sadr overpass is one of the east to west main corridors in Greater Tehran Area and embeds a large amount of traffic volume. Therefore, assessing different and alternative traffic scenarios and its modeling incorporating air pollution concerns, promotes imposition of the most environmentally preferred traffic demand management policies. This study aims to investigate different alternatives to access Sadr Overpass of Tehran using different ramps and estimating the air pollution caused by the traffic volumes in each access mode. These scenario alternatives have been evaluated using MCDM. Therefore, the different access routes via ramps of Sadr Overpass to its main lanes are considered in terms of the two formerly implemented scenarios. The first implemented scenario is defined as the air pollution caused by the traffic volume due to limitation of access that was implemented before 21 June of 2017. In this period of time, in the east to west direction, the limitation of access to Sadr Overpass was imposed via lower level Sadr ramp in between 7 to 10 AM and during the closure of this ramp, vehicles could access the overpass and Niayesh Tunnel via Qeytarieh and Kaveh ramps. In other side of the overpass, the first ramp leading the lower level is closed at 15 to 21 and vehicles could not access Sadr Expressway via this ramp. The second scenario is defined at the period of time that the limitation of access in both directions, was imposed all over during the day time permanently that is from 21 June 2017 till now.  Air pollution caused by each mode of transportation is modeled using IVE that is an International Vehicle Emission Model to simulated emissions from motor vehicles. The IVE model uses local vehicle technology levels and its distribution and includes emission factors for estimating the air pollutants. Furthermore, these scenarios have been compared using Multiple-Criteria Decision Making approach and the evaluated criteria are the emission rates of motor vehicles, velocity and level of service (LOS) of the expressway. The results show that the evaluated scenarios are ranked as per their level of priority as the first and the second implemented scenarios, respectively. Also, it is shown that in the east to west direction, closure of lower level Sadr ramp in the morning peak time of traffic volume reduces the emission rates of CO pollutants by 10 percent  in that time. Similarly, in the west to east direction, limiting the access to the lower level Sadr ramp during 16-17 hours reduces the CO emissions by 3.5 percent.