Modeling fuel consumption and emissions by taxis in Tabriz, Iran: uncertainty and sensitivity analyses.

Taxis pose a higher threat to global climate change and human health through air emissions. However, the evidence on this topic is scarce, especially, in developing countries. Therefore, this study conducted estimation of fuel consumption (FC) and emission inventories on Tabriz taxi fleet (TTF), Iran. A structured questionnaire to obtain operational data of TTF, municipality organizations, and literature review were used as data sources. Then modeling was used to estimate fuel consumption ratio (FCR), emission factors (EFs), annual FC, and emissions of TTF using uncertainty analysis. Also, the impact of COVID-19 pandemic period was considered on the studied parameters. The results showed that TTF have high FCRs of 18.68 L/100 km (95% CI=17.67-19.69 L/100 km), which are not affected by age or mileage of taxis, significantly. The estimated EFs for TTF are higher than Euro standards, but the differences are not significant. However, it is critical as can be an indication of inefficiency of periodic regulatory technical inspection tests for TTF. COVID-19 pandemic caused significant decrease in annual total FC and emissions (9.03-15.6%), but significant increase in EFs of per-passenger-kilometer traveled (47.9-57.3%). Annual vehicle-kilometer-traveled by TTF and the estimated EFs for gasoline-compressed natural gas bi-fueled TTF are the main influential parameters in the variability of annual FC and emission levels. More studies on sustainable FC and emissions mitigation strategies are needed for TTF.

An Agenda for Advancing Research and Prevention at the Nexus of Work Organization, Occupational Stress, and Mental Health and Well-Being.

Work characteristics and worker well-being are inextricably connected. In particular, the characteristics of work organization shape and perpetuate occupational stress, which contributes to worker mental health and well-being outcomes. Consequently, the importance of understanding and addressing connections between work organization, occupational stress, and mental health and well-being-the focus of this Special Issue-increasingly demand attention from those affected by these issues. Thus, focusing on these issues in the long-haul truck driver (LHTD) sector as an illustrative example, the purpose of this commentary is as follows: (1) to outline current research approaches and the extant knowledge base regarding the connections between work organization, occupational stress, and mental health; (2) to provide an overview of current intervention strategies and public policy solutions associated with the current knowledge base to protect and promote worker mental health and well-being; and (3) to propose a two-pronged agenda for advancing research and prevention for workers during the 21st century. It is anticipated that this commentary, and this Special Issue more broadly, will both echo numerous other calls for building knowledge and engaging in this area and motivate further research within complementary current and novel research frameworks.

A decomposition of the effects of the COVID-19 pandemic on changes in the motor vehicle collision related mortality in Alabama.

BACKGROUND/OBJECTIVE: Motor vehicle collisions are the leading cause of unintentional injury death in Alabama and at various points during the COVID-19 pandemic there were documented increases in the following risk driving behaviors: speeding, driving under the influence, and seat belt citations. Thus, the objective was to characterize the overall motor vehicle collision (MVC)-related mortality rate in Alabama and the contribution of each component over the first two years of the pandemic compared to before the pandemic by three different road classes: urban arterials, rural arterials, and all other road classes. METHODS: MVC data were derived from the Alabama eCrash database, an electronic crash reporting system used by police officers across the state. Data on vehicle miles traveled each year were collected from the U.S. Department of Transportation's Federal Highway Administration estimates of traffic volume trends. MVC-related mortality in Alabama was the primary outcome and year of MVC was the exposure. The novel decomposition method broke down population mortality rate into four parts: deaths per MVC injury, injury per MVC, MVC per vehicle miles traveled (VMT), and VMT per population. Poisson models with scaled deviance were used to estimate rate ratios of each component. Relative contribution (RC) of each component was calculated by taking the absolute value of the component's beta coefficient and dividing by the sum of the absolute values of all components' beta coefficients. Models were stratified by road class. RESULTS: Across all road classes combined, there were no significant changes to the overall MVC-related mortality rate (per population) and its components when comparing 2020-2022 to 2017-2019; this was due to the increased case fatality rate (CFR) being offset by decreases in the VMT rate and MVC injury rate. In 2020, among rural arterials a non-significant increased mortality rate was offset by a decreased VMT rate (RR 0.91, 95% CI 0.84-0.98, RC 19.2%) and MVC injury rate (RR: 0.89, 95% CI: 0.82-0.97, RC: 22.2%) when compared to 2017-2019. For non-arterials, a non-significant decreased MVC mortality rate was observed in 2020 when compared to 2017-2019 (RR 0.86, 95% CI 0.71-1.03). When considering 2021-2022 versus 2020, the only significant component for any road class was a decreased MVC injury rate for non-arterials (RR: 0.90,95% CI: 0.89-0.93) but this was offset by an increased MVC rate and CFR, resulting in no significant change to the mortality rate (per population). CONCLUSIONS: In a state with one of the highest MVC-related mortality rates in the country, despite decreases in VMTs per population and injuries per MVC, the MVC mortality rate per population did not change during the pandemic due in part to the contributions of an increase in the case fatality rate. Future research should determine whether the increase in CFR was associated with risky driving behaviors during the pandemic.

The Impact of the COVID-19 Pandemic on Disparities in Motor Vehicle Traffic Deaths and Injuries among North Carolina American Indians.

A Periodic Feature to Inform North Carolina Health Care Professionals About Current Topics in Health Statistics.

Influence of natural ventilation design on the dispersion of pathogen-laden droplets in a coach bus.

Natural ventilation is an energy-efficient design approach to reduce infection risk (IR), but its optimized design in a coach bus environment is less studied. Based on a COVID-19 outbreak in a bus in Hunan, China, the indoor-outdoor coupled CFD modeling approach is adopted to comprehensively explore how optimized bus natural ventilation (e.g., opening/closing status of front/middle/rear windows (FW/MW/RW)) and ceiling wind catcher (WCH) affect the dispersion of pathogen-laden droplets (tracer gas, 5 µm, 50 µm) and IR. Other key influential factors including bus speed, infector's location, and ambient temperature (Tref) are also considered. Buses have unique natural ventilation airflow patterns: from bus rear to front, and air change rate per hour (ACH) increases linearly with bus speed. When driving at 60 km/h, ACH is only 6.14 h-1 and intake fractions of tracer gas (IFg) and 5 µm droplets (IFd) are up to 3372 ppm and 1394 ppm with ventilation through leakages on skylights and no windows open. When FW and RW are both open, ACH increases by 43.5 times to 267.50 h-1, and IFg and IFd drop rapidly by 1-2 orders of magnitude compared to when no windows are open. Utilizing a wind catcher and opening front windows significantly increases ACH (up to 8.8 times) and reduces IF (5-30 times) compared to only opening front windows. When the infector locates at the bus front with FW open, IFg and IFd of all passengers are <10 ppm. More droplets suspend and further spread in a higher Tref environment. It is recommended to open two pairs of windows or open front windows and utilize the wind catcher to reduce IR in coach buses.

Evaluation of indoor environmental quality, personal cumulative exposure dose, and aerosol transmission risk levels inside urban buses in Dalian, China.

The transmission of pollutants in buses has an important impact on personal exposure to airborne particles and spread of the COVID-19 epidemic in enclosed spaces. We conducted the following real-time field measurements inside buses: CO2, airborne particle concentration, temperature, and relative humidity data during peak and off-peak hours in spring and autumn. Correlation analysis was adopted to evaluate the dominant factors influencing CO2 and particle mass concentrations in the vehicle. The cumulative personal exposure dose to particulate matter and reproduction number were calculated for passengers on a one-way trip. The results showed the in-cabin CO2 concentrations, with 22.11% and 21.27% of the total time exceeding 1000 ppm in spring and autumn respectively. In-cabin PM2.5 mass concentration exceeded 35 µm/m3 by 57.35% and 86.42% in spring and autumn, respectively. CO2 concentration and the cumulative number of passengers were approximately linearly correlated in both seasons, with R value up to 0.896. The cumulative number of passengers had the most impact on PM2.5 mass concentration among tested parameters. The cumulative personal exposure dose to PM2.5 during a one-way trip in autumn was up to 43.13 µg. The average reproductive number throughout the one-way trip was 0.26; it was 0.57 under the assumed extreme environment. The results of this study provide an important basic theoretical guidance for the optimization of ventilation system design and operation strategies aimed at reducing multi-pollutant integrated health exposure and airborne particle infection (such as SARS-CoV-2) risks.

Crash harm before and during the COVID-19 pandemic: Evidence for spatial heterogeneity in Tennessee.

Major concerns have been raised about road safety during the COVID-19 pandemic in the US, as the crash fatalities have increased, despite the substantial reduction in traffic. However, a comprehensive analysis of safety-critical events on roadways based on a broader set of traffic safety metrics and their correlates is needed. In addition to fatalities, this study uses changes in total crashes and total monetary harm as additional measures of safety. A comprehensive and unique time-series database of crashes and socio-economic variables is created at the county level in Tennessee. Statistics show that while fatal crashes increase by 8.2%, total crashes decrease by 15.3%, and the total harm cost is lower by about $1.76 billion during COVID-19 (2020) compared with pre-COVID-19 conditions (2019). Several models, including generalized least squares linear, Poisson, and geographically weighted regression models using the differences between 2020 and 2019 values, are estimated to rigorously quantify the correlates of fatalities, crashes, and crash harm. The results indicate that compared to the pre-pandemic periods, fatal crashes that occurred during the pandemic are associated with more speeding & reckless behaviors and varied across jurisdictions. Fatal crashes are more likely to happen on interstates and dark-not-lighted roads and involve commercial trucks. These same factors largely contribute to crash harm. In addition, a greater number of long trips per person not staying home during COVID-19 is found to be associated with more crashes and crash harm. These results can inform policymaking to strengthen traffic law enforcement through appropriate countermeasures, such as the placement of warning signs and the reduction of the speed limit in hotspots.

Fifteen Years of Community Exposure to Heavy-Duty Emissions: Capturing Disparities over Space and Time.

Disparities in exposure to traffic-related air pollution have been widely reported. However, little work has been done to simultaneously assess the impact of various vehicle types on populations of different socioeconomic/ethnic backgrounds. In this study, we employed an extreme gradient-boosting approach to spatially distribute light-duty vehicle (LDV) and heavy-duty truck emissions across the city of Toronto from 2006 to 2020. We examined associations between these emissions and different marginalization indices across this time span. Despite a large decrease in traffic emissions, disparities in exposure to traffic-related air pollution persisted over time. Populations with high residential instability, high ethnic concentration, and high material deprivation were found to reside in regions with significantly higher truck and LDV emissions. In fact, the gap in exposure to traffic emissions between the most residentially unstable populations and the least residentially unstable populations worsened over time, with trucks being the larger contributor to these disparities. Our data also indicate that the number of trucks and truck emissions increased substantially between 2019 and 2020 whilst LDVs decreased. Our results suggest that improvements in vehicle emission technologies are not sufficient to tackle disparities in exposure to traffic-related air pollution.

Social Efficiency of Public Transportation Policy in Response to COVID-19: Model Development and Application to Intercity Buses in Seoul Metropolitan Area.

Although more than two years have passed since the appearance of the coronavirus disease 2019 (COVID-19), few policies on public transportation have been implemented to reduce its spread. It is common knowledge that public transportation is vulnerable to COVID-19, but it has not been easy to formulate an appropriate public transportation policy based on a valid rationale. In this study, a modified SEIHR model was developed to evaluate the socioeconomic effects of public transportation policies. By applying the developed model to intercity buses in the Seoul metropolitan area, the socioeconomic efficiency of the policy of reducing the number of passengers was evaluated. The analysis showed that the optimal number of passengers decreased as the number of initially infected people increased; in addition, the basic reproduction number R0, illness cost per person, and probability of infection with a single virus were higher. However, depending on these variable conditions, the policy to reduce the number of passengers in a vehicle may not be required, so it is necessary to make an appropriate judgment according to the situation. In particular, the emergence of a new mutant COVID-19 will necessitate the development of appropriate countermeasures by comprehensively examining the change in the number of infected individuals and the fatality rate. This study can guide the development of such countermeasures.

Epidemiological progression of COVID-19 positive cases among transnational truck drivers in the East African Region.

COVID-19 triggered a range of border controls to curb the spread of the disease. Containment measures and restrictions were put in place to mitigate cross border transmission while maintaining the flow of essential goods and services in the East and Horn of Africa Region. The first cases of COVID-19 detection among truck drivers, triggered and strengthened cross-border collaboration for detecting and responding to COVID-19 pandemic. Infection was significantly common among truck drivers in the region. As at 13 January 2021, there were 3,457 reported cumulative cases among truck drivers in the EHoA region. About 2,879 (83.3%) of the cases were reported in Uganda, 374 (10.8%) cases reported in Kenya, 190 (5.5%) cases reported in Rwanda and 14 (0.4%) cases reported in South Sudan. The reduction in the number of documented new COVID-19 cases among truck drivers declined with collaborative, timely and cooperative border point screening, and so preventing COVID-19 spread in the region. With most East African countries setting the stage for reopening borders and air spaces, sustained comprehensive surveillance is crucial for maintaining the gains from the collaborative response.

Health risks of airplane boarding methods with apron buses when some passengers disregard safe social distancing.

Many airlines instituted social distancing practices to keep passengers safe during the pandemic. The practices include keeping the middle seats empty, reducing the number of passengers taking an apron bus from the terminal to the airplane, and prescribing that passengers maintain 1 m social distance of separation from other passengers in the aisle while advancing to their seats. However, not all passengers comply with a prescribed 1 m aisle social distance. Through agent-based simulations of passenger boarding when apron buses are used, we examine boarding policies adapted for the pandemic when the level of passenger compliance varies. To compare policies, we consider the duration of time that passengers are too close to other passengers while walking or standing in the aisle. We consider other health metrics from previous research and the time to complete boarding of the airplane. We find that the WilMA-Spread and Reverse-pyramid-Spread boarding methods provide favorable outcomes. Airlines should use WilMA-Spread if their primary concern is the risk to passengers while walking down the aisle and Reverse-pyramid-Spread if they want faster times to complete boarding of the airplane and reduced risk to aisle seat passengers from later boarding passengers. The level of the passengers' non-compliance with the prescribed aisle social distance can impact a health metric by up to 6.75%-depending on the boarding method and metric. However, non-compliance reduces the time to complete boarding of the airplane by up to 38.8% even though it increases the average time an individual passenger spends boarding.

State and city laws governing the use of child restraint systems in rideshare vehicles and taxicabs: requirements and responsibility.

OBJECTIVES: To identify, describe and critique state and local policies related to child passenger safety in for-hire motor vehicles including ridesharing and taxis. METHODS: We used standard legal research methods to collect policies governing the use of child restraint systems (CRS) in rideshare and taxi vehicles for all 50 states and the 50 largest cities in the USA. We abstracted the collected policies to determine whether the policy applies to specific vehicles, requires specific safety restraints in those vehicles, lists specific requirements for use of those safety restraints, seeks to enhance compliance and punishes noncompliance. RESULTS: All 50 states have policies that require the use of CRS for children under a certain age, weight or height. Seven states exempt rideshare vehicles and 28 states exempt taxis from their CRS requirements. Twelve cities have relevant policies with eight requiring CRS in rideshare vehicles, but not taxis, and two cities requiring CRS use in both rideshare vehicles and taxis. CONCLUSION: Most states require CRS use in rideshare vehicles, but not as many require CRS use in taxis. Though states describe penalties for drivers who fail to comply with CRS requirements, these penalties do not actually facilitate the use of CRS in rideshare or taxis. Furthermore, there is ambiguity in the laws about who is responsible for the provision and installation of the restraints. To prevent serious or fatal injuries in children, policy-makers should adopt policies that require, incentivise and facilitate the use of CRS in rideshare vehicles and taxis.

Monitoring SARS-CoV-2 in air and on surfaces and estimating infection risk in buildings and buses on a university campus.

BACKGROUND: Evidence is needed on the presence of SARS-CoV-2 in various types of environmental samples and on the estimated transmission risks in non-healthcare settings on campus. OBJECTIVES: The objective of this research was to collect data on SARS-CoV-2 viral load and to examine potential infection risks of people exposed to the virus in publicly accessible non-healthcare environments on a university campus. METHODS: Air and surface samples were collected using wetted wall cyclone bioaerosol samplers and swab kits, respectively, in a longitudinal environmental surveillance program from August 2020 until April 2021 on the University of Michigan Ann Arbor campus. Quantitative rRT-PCR with primers and probes targeting gene N1 were used for SARS-CoV-2 RNA quantification. The RNA concentrations were used to estimate the probability of infection by quantitative microbial risk assessment modeling and Monte-Carlo simulation. RESULTS: In total, 256 air samples and 517 surface samples were collected during the study period, among which positive rates were 1.6% and 1.4%, respectively. Point-biserial correlation showed that the total case number on campus was significantly higher in weeks with positive environmental samples than in non-positive weeks (p = 0.001). The estimated probability of infection was about 1 per 100 exposures to SARS-CoV-2-laden aerosols through inhalation and as high as 1 per 100,000 exposures from contacting contaminated surfaces in simulated scenarios. SIGNIFICANCE: Viral shedding was demonstrated by the detection of viral RNA in multiple air and surface samples on a university campus. The low overall positivity rate indicated that the risk of exposure to SARS-CoV-2 at monitored locations was low. Risk modeling results suggest that inhalation is the predominant route of exposure compared to surface contact, which emphasizes the importance of protecting individuals from airborne transmission of SARS-CoV-2 and potentially other respiratory infectious diseases. IMPACT: Given the reoccurring epidemics caused by highly infectious respiratory viruses in recent years, our manuscript reinforces the importance of monitoring environmental transmission by the simultaneous sampling and integration of multiple environmental surveillance matrices for modeling and risk assessment.

Investigating dilution ventilation control strategies in a modern U.S. school bus in the context of the COVID-19 pandemic.

Fresh air ventilation has been identified as a widely accepted engineering control effective at diluting air contaminants in enclosed environments. The goal of this study was to evaluate the effects of selected ventilation measures on air change rates in school buses. Air changes per hour (ACH) of outside air were measured using a well-established carbon dioxide (CO2) tracer gas decay method. Ventilation was assessed while stationary and while traversing standardized route during late autumn/winter months in Colorado. Seven CO2 sensors located at the driver's seat and at passenger seats in the front, middle, and rear of the bus yielded similar and consistent measurements. Buses exhibited little air exchange in the absence of ventilation (ACH = 0.13 when stationary; ACH = 1.85 when mobile). Operating the windshield defroster to introduce fresh outside air increased ACH by approximately 0.5-1 ACH during mobile and stationary phases. During the mobile phase (average speed of 23 miles per hour (mph)), the combination of the defroster and two open ceiling hatches (with a powered fan on the rear hatch) yielded an ACH of approximately 9.3 ACH. A mobile phase ACH of 12.4 was achieved by the combination of the defroster, ceiling hatches, and six passenger windows open 2 inches in the middle area of the bus. A maximum mobile phase ACH of 22.1 was observed by using the defroster, open ceiling hatches, driver window open 4 inches, and every other passenger window open 2 inches. For reference, ACHs recommended in patient care settings where patients are being treated for airborne infectious diseases range from 6 to ≥12 ACHs. The results indicate that practical ventilation protocols on school buses can achieve air change rates thought to be capable of reducing airborne viral transmission to the bus driver and student passengers during the COVID-19 pandemic.

Assessment of COVID-19-related awareness, knowledge, prevention practices and challenges faced by truck drivers in major transport cities of India: a cross-sectional survey.

OBJECTIVES: To assess COVID-19-related awareness and knowledge among truck drivers across India and report prevention practices followed, and challenges faced, by them during the COVID-19 lockdown. DESIGN: Cross-sectional study. SETTING: Delhi, Kanpur, Kolkata and Bangalore from July to September 2020. PARTICIPANTS: Data were collected in Hindi using a structured questionnaire via telephonic interviews. Minimum 200 drivers were included from each location. OUTCOME MEASURES: Sociodemographic profile, awareness regarding COVID-19, knowledge regarding infection sources, disease spread and vulnerable populations, prevention practices followed and challenges faced. Information sources were also assessed. RESULTS: Fisher's exact test and Analysis of variance (ANOVA) test were used to check for significant differences across proportions. P value less than 0.05 was considered significant. Overall, 1246 drivers were included, with 72% response rate. Of 1246 drivers, 65% were 30-50 years of age. A majority correctly answered knowledge questions regarding communicability (95%) and fatality (66%). Fifty per cent drivers were aware of treatability of the disease, while only 43% and 24% correctly reported all signs and symptoms and routes of transmission, respectively. No driver was aware of all high-risk populations. Overall Knowledge Score is significantly associated with region. Mobile phones were the primary source of information across all regions. Over two-third drivers follow all prevention practices regularly, which differed significantly across regions. Following standard prevention practices was positively correlated with higher knowledge scores and was significantly correlated with mask use. Worry about the disease was common. Less than 40% drivers received full payment for work during this period, while 25% drivers were unable to return home due to the pandemic. Seven per cent and 26% drivers had either limited or no access to food and health services, respectively. CONCLUSIONS: Awareness activities and employer provisioned social security/health insurance might safeguard this vulnerable population till the pandemic fully abates as well as in similar situations in the future.

Health and Safety Practices and Perceptions of COVID-19 in Long-Haul Truck Drivers.

OBJECTIVE: To examine long-haul truck drivers (LHTD) perceptions of COVID-19 and their use of health and safety practices. METHODS: 146 LHTD completed an online survey to collect data on their experiences with COVID-19. Data were analyzed using descriptive and inferential statistics, and thematic analysis for open-ended responses. RESULTS: LHTD were aged from 22 to 79 years (mean age 48.1 ±â€Š11.8); 82.2% were men. Almost half of the sample were not concerned about COVID-19. Those not concerned were significantly less likely to employ health and safety practices (eg, wearing masks, social distancing), were less educated and healthier. They also perceived COVID-19 to not be real or a serious threat to their health. CONCLUSIONS: Tailored education approaches are needed to provide evidence-based data on COVID-19 risks and complications.

How can ventilation be improved on public transportation buses? Insights from CO2 measurements.

Measurements of CO2 and counting of occupants were carried out in 37 public bus trips during commuting rush hours in Barcelona (NE Spain) with the aim of evaluating parameters governing ventilation inside the vehicles and proposing actions to improve it. The results show that CO2 concentrations (1039 and 934 ± 386 ppm, as average and median, during rush hours but with average reduced occupancy due to the fair to be infected by SARS-CoV-2 during the measurement period, and measured in the middle of the busses) are in the lower range of values recorded in the literature for public buses, however an improvement in ventilation is required in a significant proportion of the journeys. Thus, we found better ventilation in the older Euro 3+ (retrofitted with filter traps and selective catalytic reduction) and Euro 5 buses (average 918 ± 257 ppm) than in the hermetically closed new Euro 6 ones (1111 ± 432 ppm). The opening of the windows in the older buses yielded higher ventilation rates (778 ± 432 ppm). The opening of all doors at all stops increases the ventilation by causing a fall in concentrations of 200-350 ppm below inter-stop concentrations, with this effect typically lasting 40-50 s in the hermetically closed new Euro 6 hybrid buses. Based on these results a number of recommendations are offered in order to improve ventilation, including measurement of CO2 and occupancy, and installation of ventilation fans on the top of the hermetically closed new buses, introducing outdoor air when a given concentration threshold is exceeded. In these cases, a CO2 sensor installed in the outdoor air intake is also recommended to take into account external CO2 contributions.

Passively sensing SARS-CoV-2 RNA in public transit buses.

Affordably tracking the transmission of respiratory infectious diseases in urban transport infrastructures can inform individuals about potential exposure to diseases and guide public policymakers to prepare timely responses based on geographical transmission in different areas in the city. Towards that end, we designed and tested a method to detect SARS-CoV-2 RNA in the air filters of public buses, revealing that air filters could be used as passive fabric sensors for the detection of viral presence. We placed and retrieved filters in the existing HVAC systems of public buses to test for the presence of trapped SARS-CoV-2 RNA using phenol-chloroform extraction and RT-qPCR. SARS-CoV-2 RNA was detected in 14% (5/37) of public bus filters tested in Seattle, Washington, from August 2020 to March 2021. These results indicate that this sensing system is feasible and that, if scaled, this method could provide a unique lens into the geographically relevant transmission of SARS-CoV-2 through public transit rider vectors, pooling samples of riders over time in a passive manner without installing any additional systems on transit vehicles.

Predominant airborne transmission and insignificant fomite transmission of SARS-CoV-2 in a two-bus COVID-19 outbreak originating from the same pre-symptomatic index case.

The number of people infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to increase worldwide, but despite extensive research, there remains significant uncertainty about the predominant routes of SARS-CoV-2 transmission. We conducted a mechanistic modeling and calculated the exposure dose and infection risk of each passenger in a two-bus COVID-19 outbreak in Hunan province, China. This outbreak originated from a single pre-symptomatic index case. Some human behavioral data related to exposure including boarding and alighting time of some passengers and seating position and mask wearing of all passengers were obtained from the available closed-circuit television images/clips and/or questionnaire survey. Least-squares fitting was performed to explore the effect of effective viral load on transmission risk, and the most likely quanta generation rate was also estimated. This study reveals the leading role of airborne SARS-CoV-2 transmission and negligible role of fomite transmission in a poorly ventilated indoor environment, highlighting the need for more targeted interventions in such environments. The quanta generation rate of the index case differed by a factor of 1.8 on the two buses and transmission occurred in the afternoon of the same day, indicating a time-varying effective viral load within a short period of five hours.