How does unsustainable urbanization affect driving behavior and vehicular emissions? Evidence from Iran
Introduction
Urbanization refers to the increasing number of urban citizens due to moving the population from rural to urban areas. It is a principal challenge facing the entire world in the 21st century (Ahmed, Asghar, Malik, & Nawaz, 2020; Fan, Wang, Liu, & Liu, 2020; Sun & Huang, 2020). Urbanization is associated with a variety of disciplines including urban development, urban geography, social sciences, public health, and many others, and is also closely relevant to modernization, industrialization, and urban rationalization. Meanwhile, the socio-demographic features of human life, e.g. pubic culture, have been significantly developed during the urbanization process in the past century (Ahmed, Zafar, Ali, & Danish, 2020; Brenner, 2013; Efimov, Lapteva, & Mikhailova, 2015).
Urbanization could constitute a significant improvement in the living conditions of humans, while it has inflicted irreparable damage to our environment. Almost all human activities within the urban environments introduce various types of gaseous and particulate pollutants into the low atmosphere, thereby air pollution is one of the major environmental drawbacks of the urbanization process (Ali, Bakhsh, & Yasin, 2019; Hickey, Boscarato, & Kaspar, 2014; Orun, Elizondo, Goodyer, & Paluszczyszyn, 2018). Although developed countries have arrived at the post-urbanization stage, many of the underdeveloped and developing countries are still in the primary urbanization stage with high energy consumption and low efficiency, to which the term ‘unsustainable urbanization’ could be applied. According to the Food and Agriculture Organization of the United Nations (FAO, 2020), unsustainable urbanization is “driven not by economic opportunity but by high birth rates and a mass influx of rural people seeking to escape hunger, poverty, and insecurity” (FAO, 2020). In contrast, a sustainable urbanized city is an integrated system maintaining a balance between society, economy, and nature (Zhang et al., 2020). Unsustainable urbanization can lead to several risks such as public health problems, higher vulnerability to natural disasters, poor urban development, social instability, and many others.
It has been evidenced that some risks of unsustainable urbanization, such as social instability, could also somewhat affect human social behavior and even public culture (Alexander, Jacobs, & Smith, 2012). Social instability -a small proportion of the community’s population owns most of the community’s wealth and the rest of the community struggles to survive- might exacerbate aggressive actions/reactions in the public culture, human lifestyle, and public behavior. (Hoback, 2019) studied the strong correlation between social instability and aggressive driving. The dramatic role of aggressive driving in increasing both fuel consumption and emission of a passenger car has been reported by many previous investigators (see for example (Huang et al., 2018; Zheng, Li, van Zuylen, & Lu, 2017)).
Poor urban development is another feature of unsustainable urbanization, as a result of which urban infrastructures, such as road networks or public transportation, do not develop in proportion to the increasing urban population and rising number of cars traveling on them, resulting in common heavy traffic congestions (Lu, Li, Li, & Al-Barakani, 2021; Zhang et al., 2018). Long-time traffic congestions usually cause a range of serious economic and environmental drawbacks such as delays in the transport of goods and services, reduction of employee productivity, and air pollution (Kinnon et al., 2019; Lv et al., 2019; Shahbazi, Reyhanian, Hosseini, & Afshin, 2016). Traffic congestion has considerable impacts on driving behavior; it easily makes drivers less focused (Li et al., 2020) and/or irritable (Qi, Wen, Wu, & Qin, 2017) and/or stressful (Emo, Matthews, & Funke, 2016), all of which could cause aggressive driving reactions. Although a wide body of research has evidenced the prevailing contributions of traffic congestions to environmental transport and social characteristics of individual vehicles, the studies analyzing the impact of unsustainable urbanization on driving behavior and vehicle emissions of a fleet population are quite sparse.
Vehicular emission is primarily affected by several parameters such as vehicle speed, fuel type, route design, engine type, vehicle age, driving behavior, etc (Hickey et al., 2014; Kamble et al., 2009; Tamsanya, Chungpaibulpatana, & Limmeechokchai, 2009). Several studies have been conducted on the leading role of driving behavior in the emission of vehicles (see for example (Borlaug et al., 2020; Jaikumar, Shiva Nagendra, & Sivanandan, 2017; Yang et al., 2020)). The driving behavior of a fleet population in each region is usually evaluated by analyzing the driving cycle (DC) of that region, which is a speed-time plot illustrating different actions/reactions of the drivers. DC might be considered as the proxy of the level of urbanization in a target region. The available literature oriented around the subject of the driving cycle is reviewed in the next sections. The developed driving cycles as well as other required information, including meteorological conditions, fleet composition, fuel specifications, etc., could be delivered to the emission models for estimating the emission factors (EFs) of vehicles under real-urban conditions. Real-urban EFs could somewhat reflect the role of different socio-demographic or urban features, such as the level of urbanization, on fleet emission.
Based on the rationale above, this study seeks to fill the gap by providing new insights into the role of an unsustainable urbanization process in the driving behavior and emission of moving vehicles. Iran's large cities can be considered as proper cases for this study because most of them have experienced unsustainable urbanization in the past decades (see for example (Fanni, 2006; Tavakoli & Heydari, 2012)). The historical city of Isfahan is one of the most famous large cities in Iran. In the next section, it will be explained why applying the term ‘unsustainable urbanization’ to Isfahan makes sense. In the present study, ISFahan Driving Cycle (ISFDC) is developed and assessed against the existing national and overseas DCs to determine the role of public culture and urban development in driving behavior, as both factors are significantly affected during the unsustainable urbanization process. Furthermore, ISFDC and the other required information are entered into the model to estimate the real-urban EFs and discuss the impact of unsustainable urbanization on vehicular emissions. Finally, some emission abatement scenarios are introduced and the efficacy of each of them is discussed to provide an insight into the likely solutions.
The present paper is organized as follows. The main characteristics of the city of Isfahan are presented in the next section. The literature oriented around driving behavior and different methods of developing DCs are reviewed in Section 3. The employed method to develop ISFDC and the assessment analysis are provided in detail in Section 4. The method of estimating real-urban EFs is presented in Section 5. ISFDC and estimated EFs are all evaluated and discussed against those of other cities around the world in Section 6. Some mitigation scenarios and assessments of the efficacy of each of them are also analyzed in Section 6. Finally, the major conclusion of the study, as well as the direction of the future works are summarized in Section 7.
Section snippets
City of Isfahan
The historical city of Isfahan is considered to be the third-largest city of Iran after the capital Tehran and Mashhad (Karimi, Shetab-Boushehri, & Ghadirifaraz, 2019). Isfahan, Tehran, and Mashhad are located on the map of Iran in Fig. 1. Isfahan has experienced fairly rapid urbanization over the past two decades. The population of the city was around 700,000 in 1977 and according to Iran’s national census, it exceeded 2.13 M in 2020 (Isfahan-Municipality, 2020). The city land use has also
Review of the literature on the driving cycle
The driving cycle (DC) is a speed-time plot representing the average driving behavior in a given city or region for a type of vehicle (Galgamuwa, Perera, & Bandara, 2015; Kamble, Mathew, & Sharma, 2009). The driving cycle could be considered as a signature of driving characteristics of the city and varies from city to city or even region to region (Barlow, Latham, McCrae, & Boulter, 2009). It consists of a sequence of vehicle operating conditions including idle, acceleration, cruise, and
Route selection procedure
DCs are constructed on the instantaneous positions of the vehicles moving over the street network of the study area. Hence, instantaneous positions of a wide body of fleet should be sampled spatially and temporally to illustrate a DC representing the driving behavior of the drivers. However, sampling from the entire street network at all times is fairly impossible due to labor consumption and sampling time issues. A possible way to resolve the problem may be selecting a limited number of road
Emission factor estimation
The available emission models estimate the vehicular emission factors based on pre-defined EF libraries which were achieved/measured in places somewhat far from the study area. Hence, model users around the world have been instructed by model developers to adjust the models according to the real-world conditions of the fleet. Moreover, those models could provide real-urban EFs when they have been delivered the DC of the studied area. In this section, onboard experiments for adjusting the model
The developed driving cycle of Isfahan
During the data collection procedure, more than 60,000 speed-time data were collected in five selected routes to develop the driving cycle of Isfahan. The normal distribution of speed and acceleration of base-dataset is reported in Table 4. Besides, the speed-acceleration frequency plot of the base-dataset is presented in Fig. 4 to provide a better understanding of the speed and acceleration profiles through a successful trip in the city of Isfahan. The peak of the surface plot is on the speed
Conclusions and future works
This study was designed to shed light on the effect of unsustainable urbanization on environmental transport in terms of driving behavior and vehicular emissions. The city of Isfahan in Iran was selected as the case study because unsustainable urbanization could apply to it, due to its certain urban characteristics such as rapid population growth, poor urban development, insufficient and inefficient public transportation, etc. Unsustainable urbanization is considered here in terms of poor urban
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by the Isfahan municipality through a research project (No. 104101/88). The authors would appreciate the kind cooperation of Transportation Planning and Studies Department of Isfahan in providing the traffic data of the street network of the city.
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2021, Urban ClimateCitation Excerpt :Moreover, the pollutants VOCs and NOx are ranked as the subsequent important criteria pollutants emitted from the Isfahan MCs exhausts. The amount of VOCs contribution in the MCs exhaust (16.18%) is a notable issue when compared with similar values of LDVs, i.e. 4.83% (Ghaffarpasand et al., 2021). It seems that the VOCs contribution in the MCs exhausts is more than three times higher than the similar emissions by the LDVs exhausts.