Seoul has installed mechanical air filters in the heating, ventilation, and air conditioning (HVAC) systems of city buses to improve their indoor air quality since late 2019. We evaluated particle removal efficiencies of the filter in a wind tunnel, and clean air delivery rates (CADRs) of the systems and a household air purifier in the buses, following the test standards. The filter showed the efficiencies of 91% and 97.6%, 88% and 97.9%, and 78% and 95.2% for 0.35 μm particles and PM2.5 at 1.0m/s, 1.5m/s, and 2.0m/s, respectively. The efficiencies rose with an increase in the particle size and the filters had a minimum efficiency reporting value (MERV) rating of 15. The CADRs for PM2.5 and flow rate of the systems were 12.7m3/min and 17.9m3/min, 16.6m3/min and 25.4m3/min, 18.7m3/min and 33.6m3/min, and 23.3m3/min and 47.1m3/min on the operation mode of 1, 2, 3, and 4, respectively. The CADRs of the systems were 3.8-7.1 times higher than those of the air purifier, but single-pass removal efficiencies of the former were 0.56-0.81 lower than those of the latter.

One major concern of Seoul City is the premature failure occurrence such as fatigue cracking and rutting in the pavement. Due to the acceleration at intersections and low vehicle speed at bus stops that cause higher shear and critical strain on the pavement. Because of this, there is a need to develop a new mixture that can withstand bus stop and intersection traffic while preventing premature failure. In this study, a high modulus asphalt mixture was adapted and developed to address the cracking and rutting concerns at bus stops and intersections of Seoul City. Indirect tensile (IDT) and beam fatigue testing were conducted to determine the fatigue performance of the high modulus asphalt mixture (HMB). In addition, the behaviour of the HMB considering loading speed and temperature were investigated using the IDT dynamic modulus test. It was found that the HMB performs 3 and 1.5 times better compared to conventional asphalt using IDT and beam fatigue test respectively. Moreover, it was observed that modulus value of HMB is two times better at low frequency (high temperature) compared to conventional asphalt. The dynamic modulus value of the HMB was then used as input for bus stop and intersection scenario analyses. It was found that HMB can reduce the total thickness of the pavement around 4 to 6cm compared to the conventional asphalt. It can be concluded that because of the better fatigue and rutting performance and high modulus value of HMB at low frequency, it can perform better in bus stops and intersections. It is recommended to conduct field construction to further evaluate the performance of HMB asphalt mixtures in the field.