Real-world evaluation of driving behaviour and emission performance of motorcycle transportation in developing countries: A case study of Isfahan, Iran

Highlights

• On-board measurements performed to assess MC emission factors.

• MC EFs decrease with the vehicle speed.

• Incomplete combustion of MC fleet increases the VOCs contribution in total exhaust.

• Urban development and public culture significantly impact MC driving behaviours.

• The VOC contribution in the MC exhaust is more than that in LDVs.

• Formaldehyde and Benzene are the main toxic pollutants in Isfahan MC exhausts.

Abstract

The present study aims at a real-world assessment of the driving behaviour and exhaustive emission performance of motorcycle (MC) driving in a middle-sized city of a developing country, i.e. Isfahan, Iran. We developed the Isfahan Motorcycle Driving Cycle (IMDC) using comprehensive data collection and then compared it with the available overseas MCDCs and DC of local LDVs. Onboard experiments were also conducted on 20 test motorcycles to analyze emission performance, emission characteristics, and combustion quality of motorcycles under real-world conditions. IVE model was used to estimate the MC emission factors (EFs) according to the real-urban conditions, but it was first adjusted to the real-world measurements. Results show that MC EFs steadily decrease with vehicle speeds. Apparent discrepancies were observed between IMDC and the MC DCs overseas, while local DCs of motorcycles and LDVs follow a prevailing trend determined by the new factors of public culture and urban development. CO was the major criteria pollutant of the MCs exhaust, and formaldehyde and benzene were ranked as the first and second principal toxic gases, respectively. The air-fuel mixture control system and combustion quality of 150 and 200 cc MCs were impaired with the vehicle speed, but the same is not true for the 125 cc MCs.

Introduction

Recent emission inventories reveal that the transportation sector is one of the substantial sources of several criteria air pollutants such as carbon monoxide (CO), nitrogen oxides (NO_x), non-methane hydrocarbons (HC), and particulate matter (PM), in urban areas (Wang et al., 2016; Kwon et al., 2017; Li et al., 2017; Ghaffarpasand et al., 2020a). Motorcycles (MCs) are a popular part of the transportation fleet which provides mobility to millions of people worldwide. Over the past decades, collision records and new insurance policies have highlighted a notable decrease in the distance travelled by motorcycles in the developed countries. For example, the statistics of the Department Of Transport (DFT) in the UK report upon over 20% reduction in the distance travelled by motorcycles from 2004 to 2016 (DFT, 2017). In developing and underdeveloped countries, however, motorcycles are still typically used due to lower prices and greater fuel economy (Banitalebi and Hosseini, 2016; Mousavi et al., 2017; Shahbazi et al., 2017; Dehghani et al., 2018; Mohammadiha et al., 2018; Pouresmaeili et al., 2018; Talaiekhozani et al., 2018). More than half of the world's motorcycles are in the Asia-Pacific and Southern and Eastern Asia regions (WorldAtlas, 2021). In these regions, MCs are usually used for transportation, parcel delivery, and even cargo delivery rather than for leisure purposes. Meanwhile, the MC population in those areas has rapidly increased mainly due to the low gasoline price as well as inefficient public transportation system (Shahbazi et al., 2017). MCs are almost free of any regulations or even transport restrictions for their mobility across urban areas, while thorough technical inspections are annually required for Light-Duty Vehicles (LDVs). Due to their size, motorcycles can also flow better through the traffic and transport faster than the other fleet parts, e.g. light/heavy-duty vehicles. Hence, they have a different driving cycle and driving behaviour compared to other modes of transportation.

According to the review of the literature on the subject, (Saleh et al., 2010) developed the driving cycle of motorcycles moving over Edinburgh, UK, and Delhi, India; and utilized the chassis dynamometer test to evaluate the exhaust emissions of various types of vehicles. They found that there are significant differences between the driving cycles (DCs) of Delhi and Edinburgh. (Tong et al., 2011) developed the driving cycles of motorcycles and light-duty vehicles in Hanoi, Vietnam using on-road speed-time data. They found considerable discrepancies between the characteristics of Hanoi's DC and that of the other international DCs. (Chiang et al., 2014) developed the MCDC of Taichung, Taiwan, and characterized the emission factors using an onboard exhaust emission measurement system. Results demonstrate that the obtained MCDC is almost unique for Taichung in comparison to the MCDC of the other regions. (Iodice and Senatore, 2016) used chassis dynamometer tests to study the effect of engine operating conditions on the emission factors of 4-stoke motorcycles. They found that the emission levels depend mainly on the test driving cycles. (Hassani and Hosseini, 2016) also conducted chassis dynamometer tests to evaluate the motorcycle emissions performance in Tehran, Iran. They did not develop a new driving cycle for Tehran motorcycles and used Economic Commission for Europe (ECE) as the test-driving cycle. Their results demonstrate that Tehran motorcycles contribute to the air pollutants much more than their contribution to the total fleet or even total travels. (Sakthivel et al., 2019) studied the influence of fuel on combustion quality, emission performance, and emission characteristics of a motorcycle using the chassis dynamometer test. They found a noticeable improvement in motorcycle performance when it was fueled by ethanol-blended gasoline.

Discrepancies between the driving behaviour of MCs and LDVs have been discussed in none of the studies above. Meanwhile, the combustion quality and emission performance of MCs have been usually studied using chassis dynamometry experiments. The portable emission measurement technique is more appropriate for studying the real-world emission factors and emission performances compared with the other methods used under controlled conditions, e.g. chassis dynamometry (Chiang et al., 2014).

Considering the abovementioned issues, this paper primarily aims to gain a remarkable insight into the MC fleet in a developing country to provide a better understanding of its contribution to urban mobility and urban air pollution. For this purpose, the MC fleet of the city of Isfahan, the second most polluted city of Iran (Ghaffarpasand et al., 2020b), was selected as the case study here. The population of the Isfahan transportation fleet stands at about two million different vehicles, based on the statistics of the Isfahan traffic department in 2019, whereby the transportation sector constitutes a significant contribution to the regional air quality degradation. It should be noted that almost all the vehicles in Isfahan are fueled by fossil fuels, i.e. gasoline, diesel, and compressed natural gas. Isfahan's motorcycle fleet included 0.8 million gasoline motorcycles in 2019, based on the statistics of the Isfahan Traffic Department. Meanwhile, Isfahan motorcycles have significantly contributed to the fleet emission of the city (Ghaffarpasand et al., 2020c).

MCs of Isfahan have been usually used for cargo, parcel delivery, and as taxis in the city. The MC fleet of the city is rapidly expanding, mainly due to the low price of gasoline which is cheaper than 20 cents in late 2019, and other benefits for the MC drivers. The MCs claimed insurance costs are much lower than those for LDVs. MCs can transport over the entire city and even drive faster than LDVs on the highways of Isfahan, whereas there are certain transport restriction areas for LDVs. Meanwhile, MCs are almost free of any technical inspections, whereas annual technical inspections have been rigorously applied to the Iran LDVs for the past decade. Hence, the Isfahan MC fleet could be introduced as a unique mode of transportation in developing and under-developed countries.

In this study, Isfahan Motorcycles Driving Cycle (IMDC) was developed and compared with the available DC of Isfahan-LDVs to discuss the discrepancies of different vehicles moving over the same street network. IMDC was also compared with the other overseas MC DCs to introduce new factors which can significantly impact driving behaviour. Furthermore, the emission factors of Isfahan MCs were estimated using the International Vehicle Emission (IVE) model, adjusted using the field data, and receipt of the IMDC. Onboard real-world experiments were carried out for not only adjusting the model but also studying the emission characteristics and emission performance of the MCs in the roadside environment.

The present study is organized as follows. The employed methods for route selection, data sampling, DC development, onboard experiments, emission estimation, etc., are discussed in the next section. Isfahan motorcycle driving cycle (IMDC) is explored and assessed against the other MC DCs around the world in Section 3. The real-world emission performance of Isfahan motorcycles, the estimated MC emission factors under the real-urban conditions as well as the quality of combustion are also reported in Section 3. Finally, the main conclusion of the study and the future research directions are outlined in Section 4.