4.1. Indicators and Data
In this paper, 30 provinces and municipalities in mainland China, each referred to as a region, are selected as research samples for the study period from 2010 to 2017. This sample was also used in the research by Liu et al. [
6,
18]. To make the research results more conducive to national policymaking, this study groups these 30 regions in China into eastern, central and western areas, by adopting the official classification [
24]. Liu et al. [
45] believed that infrastructure, energy and employees are indispensable inputs in the process of road transport. The highway mileage is the most basic infrastructure investment of the road transport department, which represents the scale of the road transport system [
46]. The major energy consumption in road transport is gasoline and diesel fuel, so the consumption of gasoline and diesel is used as another input, as was done by Song et al. [
47]. Moreover, the employees are the human resource input of the road transport industry, and the number of employees is chosen as the input indicator in most studies on transport efficiency [
29]. Compared with the number of operating vehicles used by Cui and Li [
48], the number of seats in operating cars and the load capacity of operating trucks can better reflect the service capacity of operating vehicles.
The services provided by the road transport sector include passenger and freight transport, so freight and passenger volumes are used as desirable outputs by Chen et al. [
49]. However, passenger turnover and freight turnover have been used to better reflect the capacity of road transport services than passenger and freight volumes [
6,
48]. Therefore, this paper selects the passenger turnover and freight turnover of each administrative region as the desirable output indicators, which respectively represent the total number of passengers or the total weight of freight through the road transport system multiplied by the travel or transport distance [
26]. Road transport inevitably emits greenhouse gases, causes traffic accidents and produces noise, all of which can cause huge economic losses and severe social costs that require attention [
7,
50]. In addition, compared with the number of traffic accidents, the direct property loss caused by traffic accidents can more directly reflect the degree of damage to the society, so this model uses the loss to measure traffic accidents.
According to the actual situation of the road transport industry, based on previous research on the efficiency of road transport, and considering the authenticity and availability of data, this paper selected six input indicators, namely highway mileage, the number of employees, gasoline consumption, diesel consumption, tonnage of road operating truck and passenger seating capacity. Two desirable output indicators were selected, namely passenger turnover and freight turnover. Moreover, noise, CO2 emissions and direct property losses caused by traffic accidents are employed as undesirable outputs.
The above input-output data are all available from the China energy statistical yearbook 2011–2018 and China statistical yearbook 2011–2018. Due to the lack of equivalent sound levels for road transport in some provinces, this paper selects the equivalent sound level in provincial capitals as the noise data index. Unfortunately, there are no direct statistical data about CO
2 emissions from road transport in these regions. However, carbon dioxide mainly comes from the consumption of automobile fuel, so we chose the consumption of gasoline and diesel during road transport as a measure corresponding to the carbon dioxide emissions. Referring to previous studies by Wang and He [
17] and Liu et al. [
45], carbon dioxide emissions can be calculated using Equation (7).
In Formula (7), CE stands for carbon dioxide emission, and
,
,
, and
respectively represent the consumption, carbon content factor, hydrocarbon coefficient, and equivalent thermal energy of the
ith region. The fraction 44/12 denotes the conversion coefficient of carbon into carbon dioxide, which is the ratio of the relative molecular weight of carbon dioxide to the relative molecular weight of carbon, so
is the coefficient of carbon emission about the
ith energy. The data on the consumption of gasoline and diesel oil during road transport comes from the China energy statistical yearbook 2011–2018. According to Formula (7), the carbon dioxide emissions of each region can be calculated. The general input-output statistics for road transport are shown in
Table 1.
4.2. Results and Analysis
The DDF model explained above was used to evaluate the environmental efficiency of road transport in 30 regions of China from 2010 to 2017, and MATLAB software was used for computing the optimal solution β * in the model. By the formula
,
was converted to be an environmental efficiency value θ, which is less than or equal to 1. The empirical results are given in
Table 2 below.
4.2.1. Overall Environmental Efficiency Analysis
As can be seen from the
Table 2, from 2010 to 2017, the overall environmental efficiency score of road transport increased from 0.8851 to 0.9633, with an overall average score of 0.9275. The number of regions with an environmental efficiency score of 1 rose from 13 to 22 between 2010 and 2017. The environmental efficiency of road transport of seven regions remained unchanged from 2010 to 2017, with a fixed score of 1, namely Anhui, Hunan, Guangdong, Sichuan, Guangxi, Hainan and Ningxia. Among these regions with the best environmental efficiency, there are both economically developed regions, such as Guangdong, and relatively underdeveloped regions, such as Guangxi and Ningxia. This shows that a series of macroeconomic control policies adopted by the Chinese government has achieved some success. Moreover, the results show that there is no direct correlation between the development of regions and their environmental efficiency of road transport.
Suppose that the seven efficient regions rank first. Shanghai, Zhejiang and Fujian, which are relatively developed regions, did not rank well among the 23 inefficient regions, ranking 12th, 13th and 20th, respectively. The average environmental efficiency of the road transport of Shanxi, Yunnan, Fujian, Heilongjiang and Jilin is relatively low; among these, Shanxi has the lowest score with an average value of 0.6699, and it is the only region with a value less than 0.7. Meanwhile, the four provinces of Yunnan, Fujian, Heilongjiang and Jilin also performed poorly, with efficiency values below 0.8 (0.7795, 0.7887, 0.7473 and 0.7826). Hebei, Liaoning, Jiangxi, Henan, Chongqing, Guizhou, and Gansu have experienced a transition from inefficiency to efficiency, and have remained efficient in recent years.
On the whole, the environmental efficiency of road transport increases over time. With the development of science and technology, the modern transport network system has been continuously optimized and improved. Under the guidance and support of a series of relevant policies issued by the state, the road transport industry will have bright development prospects.
4.2.2. Environmental Efficiency Analysis in Different Areas
Figure 1 shows the changing trend of environmental efficiency in the whole country, as well as the eastern, central and western areas. The four curves in
Figure 1 show an upward trend over time, indicating that the environmental efficiency of road transport is improving from the perspective of development trend, even though the efficiency fluctuates. For the eight years from 2010 to 2017, the eastern area’s environmental efficiency curve is above the overall environmental efficiency curve, while the central area’s environmental efficiency curve is below the overall environmental efficiency curve. For the two years from 2010 to 2011, the curve of the western area is below the overall level. For the three years from 2012 to 2014, the curve of the western area is above the overall level. For 2015 to 2017, the curve of the western area is slightly below the overall level. In 2014, the reduction of environmental efficiency of road transport in eastern areas was large, while that in central and western was small. In 2015, the environmental efficiency of the eastern and central areas increased significantly, while that of the western area increased less than that of the eastern and central areas. The fluctuation range of the environmental efficiency of road transport varies in different regions, and there are obvious regional differences in environmental efficiency of road transport, with the most obvious gap being seen for 2013. With the comprehensive development of the national transport industry, the gap between regions is narrowing. In particular, the environmental efficiency difference between the three areas has been greatly reduced since 2014.
According to
Table 3, differences in the environmental efficiency of road transport can be found in different areas. For 2010 to 2017, the overall average efficiency of road transport is 0.9275. The eastern area with better economic development has the highest average level of environmental efficiency of road transport (0.9582), followed by the western area (0.9251), with the central area having the lowest average efficiency (0.8926). In addition, the western area has the largest efficiency improvement range, with the environmental efficiency score increasing from 0.8482 in 2010 to 0.9598 in 2017; that is, an increase of 0.1166. The environmental efficiency of the central area increased from 0.8607 to 0.9450, an increase of 0.0843. The eastern area figure changed from 0.9388 to 0.9815, increasing by 0.0427.
Regional differences in road transport in China are mainly due to the heterogeneity of economic development level and environment in the areas containing the regions. The eastern area is located in the coastal area, with a developed business system, a strong ability to utilize foreign capital, highly developed infrastructure, great demand for road transport, and many environmental regulations that restrict undesirable output. Therefore, the environmental efficiency value of road transport in the eastern area is relatively high, which is consistent with the empirical results. The central area is an inland region with a large population and a relatively backward level of resources and technology. Furthermore, central China has few environmental regulations and the harmful outputs generated in the process of road transport are not treated promptly, which leads to the lowest environmental efficiency of road transport in these three areas. The western area has a diverse topography, a small population base, and a simple road transport system, so, correspondingly, lower levels of carbon emission, safety accidents, noise pollution, and other adverse outputs compared with the central area. Thus, the environmental efficiency score of road transport in the western area lies between those of the eastern and central areas.
Although there are differences in the average environmental efficiency of the three areas, the differences among them are narrowing. This trend shows that China has achieved some progress in promoting economic development and protecting the ecological environment in the central and western areas, but further improvement remains necessary.
4.2.3. Convergence Analysis at Area Level
Using Formula (4) above, we conducted σ convergence tests for the whole country and three areas from 2010 to 2017. The results of σ convergence testing are shown in
Figure 2. From the point of view of overall environmental efficiency, the standard deviation of environmental efficiency gradually decreased from 2010 to 2013, showing the characteristics of convergence. However, the value of σ rebounded in 2014 and then gradually declined after that, until the value of σ rebounded for a second time in 2017, though the jump was less than that in 2014. Therefore, it can be concluded that during the sample period, the gap in the environmental efficiency between different areas in China is narrowing. That is, there is σ convergence of the national environmental efficiency of road transport. Compared with the overall standard deviation curve, the variation trend of the western area is basically the same as that of the whole country, and the value of σ from 2015 to 2017 is less than that of 2013. Similarly, we can judge that σ convergence exists in the western area.
The trend of change in the eastern and central areas is similar to that in the western area, but the range of change is different. In particular, the standard deviation of the eastern and central areas increased significantly in 2014, and then showed a downward trend, but it was still slightly greater than that of 2013, which is different from the western area. It can be concluded that σ convergence existed in the eastern and central areas at different stages. According to the above analysis, weak σ convergence exists in the eastern and central areas. In addition, the standard deviations of environmental efficiency, from the smallest to the largest, are those of the eastern area, western area, whole country and central area. This phenomenon shows that, compared with the central and western area, the difference in environmental efficiency of road transport between regions within the eastern area is the smallest, and the difference among the central areas is the largest.
Table 4 shows that the absolute convergence coefficient of environmental efficiency in the whole country is −0.0995 and passes the significance test at the 1% level, which indicates that the interprovincial environmental efficiency converges to a stable level in China. Moreover, the convergence coefficients of the western, eastern and central areas are −0.1098, −0.1090 and −0.0876, respectively, and all of them pass the significance test at the 1% level, showing that absolute convergence exists in the three areas. That is, the provinces with low environmental efficiency of road transport will gradually catch up with the provinces with high environmental efficiency and finally reach convergence. The western area ranks first in efficiency convergence rate, followed by the eastern area, the whole country and the central area, in that order.
Table 5 shows that the conditional convergence coefficients of the whole country, eastern area and western area are −0.4849, −0.6403 and −0.4968, respectively; these are all significant at the 1% level. In contrast, the convergence coefficient in the central area is −0.3466 and significant only at the 5% level. These results mean that each area has its own steady level and converges to that level.