Research on the impact of transportation infrastructure construction on urban sustainable development

Abstract

The construction of transportation infrastructure is an important driving force to promote the sustainable development of Chinese cities. However, the “extensive” and “extensive” urban development mode restricts the sustainable development of Chinese cities. This paper establishes a theoretical hypothesis that transport infrastructure construction affects urban sustainable development, uses the panel data of Chinese cities from 2006 to 2021 to empirically analyze the impact and mechanism of transport infrastructure construction on urban sustainable development, and explores the heterogeneity caused by differences in sample regions and time intervals. The results show that: (1) Baseline regression shows that transport infrastructure construction can significantly promote the improvement of urban sustainable development, and the robustness test using alternative variables and the endogeneity test of instrumental variables support the baseline estimate results. (2) The results of heterogeneity analysis show that the improvement effect of transport infrastructure construction on large-scale cities is greater than that on small-scale cities, the improvement effect of transport infrastructure construction on central and western regions is greater than that on eastern regions, and the improvement effect of transport infrastructure construction on provincial capitals is greater than that on non-provincial capitals. (3) The results of the transmission mechanism show that the improvement of transportation infrastructure construction can promote sustainable urban development by promoting technological innovation and employment scale upgrading. This study further evaluates the economic effects of transportation infrastructure construction and provides empirical evidence for improving urban sustainable development.

Introduction

For a long period of time, China’s economic growth mode relied on high input and high consumption. Although this allowed the economy to maintain a high growth rate, it also brought many deep-seated problems. Labor costs are rising, resource waste is serious, environmental pollution is becoming more restrictive, and the extensive mode of development is unsustainable. However, in recent years, with the rapid development of China’s economy from a stage of high-speed growth to a stage of high-quality development and the rapid progress of a new generation of digital intelligence technologies (such as cloud computing, big data and blockchain), sustainable development has emerged as a new development model of high-quality economic development. The Central Committee of the Communist Party of China and The State Council have successively issued the Outline of Building a Strong Transport Country, the Outline of National Comprehensive Three-dimensional Transport Network Planning, Opinions on Accelerating the Construction of Ecological Civilization, Notice on the Construction Plan of Innovation Demonstration Zones for Implementing the 2030 Agenda for Sustainable Development (Guofa [2016] No. 69), and on Building a more complete market-based allocation system for Factors Documents such as the Opinions of the CPC Central Committee and The State Council on Establishing and Improving the System, Mechanism and Policy System for Integrated Urban and Rural Development emphasize in particular that transportation is an important support for building a great modern socialist country in all respects, giving full play to its basic, guiding, strategic and service-oriented role in economic and social development, and providing strong support for decisively building a moderately prosperous society in all respects. The important significance in the development of national economy. Therefore, how to promote the sustainable development of urban transportation infrastructure construction is an urgent problem for the current government to solve.

As an important support for China to fully build a modern socialist power, transportation infrastructure is the key support for testing the status of cities and core competitiveness; As an essential attribute of high-quality development and an important symbol of the construction of China’s modern socialist power, urban sustainable development is a banner for the high-quality development of China’s economy. As an important engine for China’s high-quality development, transportation infrastructure construction has important practical significance and times value for urban sustainable development. However, in the process of enabling sustainable urban development, transportation infrastructure construction also has many social, technical and institutional problems, resulting in regional differences in urban sustainable development. Therefore, how to use transportation infrastructure construction to promote urban sustainable development has become a hot issue that needs to be solved in current research. The exploratory research in this field at home and abroad mainly includes the following aspects.

First, there are some analytical frameworks about transport infrastructure and urban sustainable development, and domestic and foreign scholars have conducted a lot of studies based on different research perspectives. They found that the role of traffic gathering population can promote the efficiency improvement of the high population density-dependent service industry and eliminate the potential cost increase caused by efficiency lag. The opening of high-speed rail significantly promotes the improvement of the urban industrial structure index^1,2, transportation infrastructure can improve the added value of county industry³, transportation infrastructure has a positive spillover effect on economic growth as a whole⁴. Transportation infrastructure promotes economic growth by expanding enterprise scale and enhancing market vitality⁵. The opening of high-speed rail effectively promotes the economic growth of county-level cities with high-speed rail⁶, expressway connectivity can effectively improve the level of market access and thus affect the market integration development between cities⁷. Transportation infrastructure effectively reduces domestic trade costs by improving market accessibility, significantly and stably improves enterprise productivity, and promotes domestic market integration⁸. Expressway accessibility has a significant promoting effect on the optimization of resource allocation efficiency of manufacturing industry in non-central cities⁹. In general, most of these studies use traffic mileage and traffic density to depict transportation infrastructure, and the impact effects involve some of the indicators (such as promoting industry, economy, market, etc.) in the three dimensions of urban sustainable development (social sustainable development, economic sustainable development and environmental sustainable development). It also provides guidance for the study of the positive impact of transportation infrastructure on urban sustainable development.

Secondly, the positive impact of transportation infrastructure on technological innovation has also accumulated some achievements. Some scholars have pointed out that hub economy mainly promotes industrial synergistic agglomeration by improving innovation activity, alleviates spatial resource misallocation, and drives the construction of a national unified technology big market¹⁰, and transportation infrastructure network significantly increases the total amount of foreign economic relations through labor capital and technological factors¹¹, the opening of metro significantly reduces the commuting cost and improves the enterprise’s R&D innovation and talent attraction to promote the improvement of enterprise productivity¹². It can be seen that these studies have found that transport infrastructure has a positive and significant relationship with innovation activities, technological factors, and enterprise R&D innovation. Although no studies have directly verified the impact of transport infrastructure on urban sustainable development through technological innovation, these research results with strong correlation have been found. Research into the impact of transport infrastructure on sustainable urban development through technological innovation increases the value potential of research.

Finally, there is a positive correlation between transportation infrastructure and employment scale. Relevant scholars have verified that the construction of transportation infrastructure improves the level of urban labor supply and excavates the potential of urban market¹³, and airport transportation services promote advanced manufacturing industry, adjust factor ratio, reduce factor cost and improve labor productivity of advanced manufacturing industry by increasing labor and saving intermediate goods¹⁴, the income increase effect of urban-rural transportation integration on rural residents is enhanced with the increase of the average education level of county residents and the proportion of working-age population¹⁵, and the transportation infrastructure network significantly increases the total amount of foreign economic relations through labor capital and technological factors¹⁶, transportation and communication expenditure has a positive promoting effect on agricultural labor productivity growth¹⁷, which provides a good foundation for further development of this study. It can be seen that, in general, these research results can be summarized as follows: transportation infrastructure has a positive correlation with urban labor supply level, labor factors, labor quality and labor productivity, and employment scale has a significant role in promoting economic growth, enterprise investment, regional innovation, common prosperity and healthy industry development. Although there are no studies directly verifying the impact of transportation infrastructure on urban sustainable development through employment scale, these strongly correlated research results provide effective clues for studying the impact of transportation infrastructure on urban sustainable development through employment scale.

Based on the above existing literature, this paper discusses the correlation effects of transport infrastructure on industry, market and regional economy on urban sustainable development, and also discusses the one-way impact of transport infrastructure on urban sustainable development through intermediary variables (technological innovation and employment scale). However, in terms of transportation infrastructure, these studies use highway mileage and highway density in provincial panel data to depict the level of transportation infrastructure construction, ignoring the impact of freight volume as a proxy indicator of transportation infrastructure on urban sustainable development. Although highway mileage and highway density have certain theoretical significance in describing transportation infrastructure. However, from a practical point of view, the freight volume directly reflects the actual use efficiency, carrying capacity, comprehensive coordination capacity and management level of urban transportation infrastructure. Efficient freight volume means that the urban transportation infrastructure network has been fully utilized to meet the needs of urban economic development. In terms of the impact of transportation-based facilities on urban sustainable development, although there have been empirical studies on urban sustainable development, there are no substantive studies on the impact of transportation-based facilities on urban sustainable development. There is also no literature research on the establishment of the transmission mechanism of “transportation infrastructure construction - technological innovation and employment scale - urban sustainable development promotion” and in-depth analysis.

Therefore, this paper makes full use of the urban panel data from 2006 to 2021 to build an indicator system of urban sustainable development capability from three dimensions of social sustainable development, economic sustainable development and environmental sustainable development. The indicator system of urban sustainable development capability fully considers the people-oriented development concept, and assigns each secondary index based on the entropy method. Measure the urban sustainable development index, and empirically test the impact of transportation infrastructure construction level on urban sustainable development. At the same time, based on the two-stage intermediary effect model, this paper further discusses the relationship between transportation infrastructure construction level and urban sustainable development ability from the perspectives of technological innovation and employment scale, establishes the transmission mechanism of “transportation infrastructure construction - technological innovation and employment scale - urban sustainable development enhancement”, and clarifies their internal logic.

Compared with the existing research, the innovation of this research is as follows: (1) The paper takes the lead in using cargo volume to describe the level of transportation infrastructure construction in the world; (2) The paper constructs a human-centered urban sustainable development index system from three dimensions of social sustainable development, economic sustainable development and environmental sustainable development on a global scale; (3) The paper takes the lead in constructing the transmission mechanism of “Transportation infrastructure construction - technological innovation and employment scale—urban sustainable development promotion” to analyze the relationship between transportation infrastructure and urban sustainable development in the world; (4) This paper adopts the research method of mechanism transmission, combines traffic engineering, geography, sociology, economics, environmental science and sustainable development theory, uses a large number of empirical data, and combines quantitative analysis and qualitative research to deeply explore the specific impact mechanism of transportation infrastructure construction level on urban sustainable development ability. It provides a new perspective for analyzing the relationship between the level of transportation infrastructure construction and urban sustainable development. (5) The paper also puts forward targeted policy suggestions, which provides an important reference for the government’s decision-making.

The overall structure of this paper is as follows: the first part is the introduction, which describes the research background, draws out the research problems, combs the relevant literature of the research status, draws the research gaps, puts forward the research innovation points and research contributions, and explains the research framework of this paper. The second part is the research hypothesis; The third part is the research design, including model setting, variable description and data source; The fourth part is the analysis of empirical results, including baseline regression analysis, robustness test, endogeneity test, heterogeneity test and intermediary test. The fifth part is conclusion and suggestion.

Theoretical analysis

Transportation infrastructure as a direct mechanism of urban sustainable development

First, promote the economic growth Angle. Efficient transportation network can shorten the spatial and temporal distance between regions, reduce logistics costs, and promote trade^18,19. For example, the construction of transportation facilities such as highways, railways and aviation can accelerate the circulation of commodities, improve the accessibility of the market, attract more investment and business activities, and then promote the development of related industries, such as manufacturing, logistics, tourism, etc., thus promoting the development of urban economy.

Secondly, optimize the urban space Angle. Reasonable planning of transportation network can guide the flow of urban population and industries to regions with more development potential, reduce urban congestion and pollution, and improve the overall operation efficiency of the city²⁰. At the same time, the improvement of transportation facilities can also promote the development of surrounding areas, promote the integrated development of urban and rural areas, realize the integration of urban and rural areas, and promote the balanced development of various regions within the city.

Thirdly, improve the quality of people’s livelihood. Convenient traffic conditions can shorten residents’ commuting time, improve travel efficiency, and reduce the inconvenience caused by traffic congestion and accidents²¹. In addition, the construction of transportation facilities can also improve the public service level of the city²². For example, the popularization and optimization of public transportation can facilitate residents’ travel and shopping, and improve the livable quality of life of the city.

From the second, promote green development Angle. By developing green transportation and encouraging green travel, the use of private cars can be reduced, transportation emissions and energy consumption can be reduced, and the pressure on the environment can be reduced²³. At the same time, the construction of transportation facilities can also promote the promotion of green clean energy and low-carbon technologies, such as electric vehicle charging stations, intelligent transportation systems, etc., to provide strong support for the green transformation of cities²⁴.

Finally, enhance the city competition Angle. A city with an efficient and convenient transportation network can more easily attract the inflow of production factors such as talent, capital and technology, thus driving the innovative development of the city. At the same time, the improvement of transportation facilities can also enhance the brand image and popularity of the city, attract more tourists and investors, promote the prosperity and development of the city, and enhance the competitiveness of the city²⁵.

Therefore, hypothesis 1 is put forward: transportation infrastructure can promote urban sustainable development.

The indirect mechanism of transport infrastructure to urban sustainable development

Technological innovation perspective

• (1) From the perspective of the positive effect of transport infrastructure construction on technological innovation, transport infrastructure, as An important support for sustainable urban development, has a direct impact on the operational efficiency and innovation capability of enterprises²⁶. Some studies have emphasized the important role of the construction level of transportation infrastructure in promoting innovation activities, and believe that China’s highway construction has a significant positive impact on innovation activities, and the construction and optimization of the construction level of transportation infrastructure should be continued in the future to better promote the development of innovation activities²⁷. Through empirical analysis, some scholars found that the improvement of the quality of cities with better ecological environment and urban service conditions, focusing on the concentration of universities, transportation hubs, metropolitan areas, not only significantly promoted the innovative development of the region, but also showed significant spatial spillover effects on the surrounding areas²⁸.

• (2) From the perspective of the promoting effect of technological innovation on urban sustainable development, big data improves the quality level of intermediate goods and promotes technological progress through the “multiplier effect” to continuously promote economic growth, and the “multiplier effect” of big data will be amplified with the increase of its “application degree”²⁹. Some scholars have found that the impact of R&D investment and SG&A costs on productivity growth presents a short-term inhibitory effect, but it will effectively improve productivity in the long run³⁰. Some scholars have found empirically-that a sound intellectual property protection system and digital infrastructure will increase the positive impact of digital technology innovation on enterprise productivity³¹.

Therefore, hypothesis 2 is proposed: transportation infrastructure has a positive effect on technological innovation to promote urban sustainable development.

Employment scale perspective

• (1) From the perspective of the effect of transportation infrastructure construction on the optimal allocation of employment scale, some scholars have pointed out that China’s transportation infrastructure has a resource reallocation effect and that China’s transportation infrastructure affects the efficiency of urban resource reallocation through three mechanisms: factor flow (flow of various production factors such as labor, capital, technology and data), market access and production transfer³². In addition, industrial upgrading, financial development, transportation infrastructure and digital economy will widen the gap between regional groups³³. Therefore, the fact that transportation infrastructure can enhance entrepreneurial activity and affect employment scale proves that there is a positive relationship between the construction level of transportation infrastructure and employment scale, and that transportation infrastructure can optimize the allocation of labor force representing employment scale.

• (2) From the perspective of the driving effect of employment scale on sustainable urban development, labor flow can promote the convergence of regional economic disparities when highly skilled workers are not considered³⁴. Labor market reform significantly increases the employment scale, per capita salary and corporate performance of enterprises by removing household registration barriers, thus increasing the labor income share³⁵. These studies use the number of employment in urban units to indicate the scale of employment, which is precisely in line with the increase in the number of employment in urban units under the removal of household registration barriers, which is conducive to improving the share of labor income and promoting sustainable urban development.

Therefore, hypothesis 3 is proposed: the effect of transportation infrastructure on the optimal allocation of employment scale to promote sustainable urban development.

Research design

Model setting

In order to investigate the impact of transportation infrastructure construction on urban sustainable development, this paper constructs a fixed effect model as follows:

$$\ln \left( {se{d_{it}}} \right)={\alpha _0}+{\beta _1}\ln \left( {traffi{c_{it}}} \right)+{\beta _2}contro{l_{it}}+{\delta _t}+{\gamma _i}+{\varepsilon _{it}}$$

(1)

The explained variable in model (1) $se{d_{it}}$ represents i the city t‘s annual sustainable economic development, the subscript irepresents the city, represents the year, and the core explanatory variable is tthe logarithm of $contro{l_{it}}$transportation infrastructure. $\ln \left( {traffi{c_{it}}} \right)$To control the set of variables, control other factors that affect sustainable economic development, and prevent model estimation errors caused by omitted variables. ${\delta _t}$and ${\gamma _i}$are the fixed effects of controlling city and year respectively, and ${\varepsilon _{it}}$are the random error terms.

Based on the intermediary variable model, the mechanism of transport infrastructure construction on urban sustainable development is further tested, and the intermediary effect model is constructed as follows:

$$\ln lpM{Y_{sjt}}={\partial _0}+{\partial _1}tra{n_{sjt}}+{\partial _2}tra{n_{jt}}+yea{r_t}+industr{y_s}+regio{n_j}+{\mu _{sjt}}$$

(2)

$${D_{sjt}}={\eta _0}+{\eta _1}tra{n_{sjt}}+{\eta _2}{Z_{jt}}+yea{r_t}+industr{y_s}+regio{n_j}+{\delta _{sjt}}$$

(3)

$$\ln lpM{Y_{sjt}}={\lambda _0}+{\lambda _1}tra{n_{sjt}}+{\lambda _2}{D_{sjt}}+{\lambda _3}{Z_{jt}}+yea{r_t}+industr{y_s}+regio{n_j}+{\zeta _{sjt}}$$

(4)

Among them, $\ln lpM{Y_{sjt}}$and $tra{n_{jt}}$are respectively the ${\text{j}}$city’s economic sustainable development and transportation infrastructure level in t year, Z is the set of control variables; D is the intermediary variable, specifically including employment scale ( is ) and technological innovation (ri) .

Variable description

Explained variable

As for the explained variable of urban sustainable development in this paper, mainly referring to the research of Zhang and Tang³⁶, the index system of urban sustainable development is constructed from a total of 23 basic indicators from three dimensions of social sustainable development ability, urban sustainable development ability and environmental sustainable development ability, and each basic indicator is further weighted based on the entropy method. Table 1 shows the definition and weight of each basic indicator. At the same time, the specific steps of weighting based on entropy are as follows:

• (1) Standardization of index data: Referring to the research of Zhang and Tang³⁶, based on the principles of scientificity, comparability and availability of index selection, principal component analysis 11 was used to screen a large number of indicators and obtain effective indicators affecting urban sustainable development. First of all, the indicators are standardized, and the calculation steps are as follows: Determine the standard value of each indicator, The standard value of a positive indicator is the maximum value of its sequence $\hbox{max} ({x_{ij}})$. The standard value of a negative indicator is the minimum value of its sequence $\hbox{min} ({x_{ij}})$. Use the range method to standardize the indicators, the following equation is obtained:

  $${\text{Positive \, indicators}}:{x^{\prime}}_{{ij}}=\frac{{{x_{ij}} - \hbox{min} ({x_{ij}})}}{{\hbox{max} ({x_{ij}}) - \hbox{min} ({x_{ij}})}}$$

  (5)
  $${\text{Negative \, indicators}}:{x^{\prime}}_{{ij}}=\frac{{\hbox{max} ({x_{ij}}) - {x_{ij}}}}{{\hbox{max} ({x_{ij}}) - \hbox{min} ({x_{ij}})}}$$

  (6)

  In the formula, ${x^{\prime}}_{{ij}}$is the standardized indicator value, $xij$is i the th observed value of the th indicator j, $\hbox{max} ({x_{ij}})$is the standard value of +, $\hbox{min} ({x_{ij}})$is the standard value of -.

• (2) Establishment of indicator weight: Use the entropy weight method to determine the indicator weight. The calculation steps are as follows.

  The indicator sequence consists of n samples, each sample has m indicators, and the following original data matrix is constructed:

  $$R=\left[ {\begin{array}{*{20}{c}} {{r_{11}}}& {{r_{12}}}& \cdots & {{r_{1m}}} \\ {{r_{21}}}& {{r_{22}}}& \cdots & {{r_{2m}}} \\ \cdots & \cdots & \cdots & \cdots \\ {{r_{n1}}}& {{r_{n2}}}& \cdots & {{r_{nm}}} \end{array}} \right]$$

  (7)

  After standardization using formula (3), the matrix R’ = ($\:\text{x}{\prime\:}\text{i}\text{j}$) n*m is obtained, then the proportion of the j-th evaluation index in the i-th evaluation object is:

  $${s_{ij}}=\frac{{{x^{\prime}}_{{ij}}}}{{\sum\limits_{{j=1}}^{m} {{x^{\prime}}_{{ij}}} }},1 \leqslant j \leqslant m;$$

  (8)

  Calculate j the entropy value of the index ${h_j}$:

  $${h_j}= - \frac{1}{{\ln m}}\sum\limits_{{j=1}}^{m} {{s_{ij}}} \ln {s_{ij}}$$

  (9)

• (3) ${h_j}$Calculate the difference ${\alpha _j}$value based on the entropy value:

  $${\alpha _j}=1 - {h_j}$$

  (10)

• (4) Calculate indicator weight ${w_j}$:

  $${w_j}=\frac{{{\alpha _j}}}{{\sum\limits_{{j=i}}^{p} {{\alpha _j}} }}$$

  (11)

According to the above formula, the entropy method is adopted to calculate the weight, and the calculation results are shown in Table 1.

Table 1 Evaluation index system and weights.

Explanatory variable

$\ln \left( {traffi{c_{it}}} \right)$Log value of transportation infrastructure. Regarding the measurement variables of transportation infrastructure, many studies use traffic density indicators to measure the development level of transportation infrastructure. In this paper, the sum of road freight volume and railway freight volume is used to describe the level of regional transportation infrastructure construction. The level of urban transportation infrastructure construction is an important indicator to measure a city’s transportation capacity, efficiency and residents’ travel convenience. Compared with the simple road mileage (including road mileage and railway mileage), the freight volume can more comprehensively reflect the level of a city’s transportation infrastructure construction, mainly for the following reasons:

• (1) The freight volume directly reflects the actual use efficiency and carrying capacity of transportation facilities. Even if a city has a large road and rail network, if the utilization rate of these facilities is low and the freight volume is insufficient, then the level of infrastructure construction is not high.

• (2) The freight volume reflects the comprehensive coordination ability and management level of the urban transportation system. Good transportation infrastructure not only includes the physical road and railway construction, but also includes the supporting traffic management, scheduling, security and other systems. Efficient passenger and cargo traffic means that these systems work together to ensure smooth, safe and orderly traffic.

• (3) Freight volume is also an important indicator to measure the sustainable development ability of urban transportation. With the acceleration of urbanization and population growth, the demand for urban transportation will continue to increase. If the level of transportation infrastructure construction of a city can support and promote the continuous growth of passenger and cargo traffic, it indicates that it has a strong sustainable development ability.

Therefore, the freight volume is more comprehensive and accurate than the road mileage to reflect the level of a city’s transportation infrastructure construction.

Intermediate variable

• (1) Technological innovation: Refer to Zheming Liu et al.³⁷, according to the principles of scientific selection, comparability and availability of indicators, the number of authorized invention patents per 10,000 people is selected to represent technological innovation.

• (2) Employment scale: According to the research of Ma Fei et al.³⁸ and the principles of scientificity, comparability and availability in the selection of indicators, the employment number of urban units is selected to represent the employment scale。.

Control variables

In order to evaluate the impact of transportation infrastructure construction on urban sustainable development more comprehensively and accurately, other factors that may have potential impact on urban sustainable development need to be controlled. This paper refers to the domestic research on urban sustainable development by Zhang Degang and Tang Yufu³⁶. This paper selects the level of external openness (the ratio of import and export of goods to GDP), the degree of foreign investment dependence (calculated as the ratio of foreign direct investment to GDP of each city), the degree of government intervention (the ratio of general budget expenditure to GDP), the level of human capital (expressed as the logarithm of the per capita years of education of each city), and the urbanization rate (the proportion of non-agricultural population in the total population of each region) The influence of urbanization development level in each region on urban sustainable development) is taken as the control variable of the model。

Data source

This paper selects the urban panel data from 2006 to 2021, all of which come from China Urban Statistical Yearbook. For individual missing data, interpolation is used to calculate. For individual cities can not find complete data will be deleted. The descriptive statistics of each variable are shown in Table 2.The results show that the mean value of urban sustainable development is 0.029, the minimum value is 0.0167, and the maximum value is 0.6810, indicating that there are obvious differences in the sustainable development level of Chinese cities, mainly because the Chinese government has consciously regulated the urban development through the formulation and implementation of a series of policies. These policies include regional development strategy, industrial policy, environmental protection policy, etc., which have different implementation intensity and effect in different cities, thus affecting the sustainable development level of cities. The mean value of transportation infrastructure construction is 1.454, the minimum value is 0.0552, and the maximum value is 55.4500, indicating that there are obvious differences in the level of transportation facilities in Chinese cities. This is mainly because policy orientation and strategic planning are important factors affecting the level of urban transportation facilities. In urban planning, the government will formulate corresponding transportation facilities construction plans according to the city’s positioning, development direction, population size and other factors. Some cities may pay more attention to the development of public transportation, such as subway, bus, etc., to alleviate the problem of urban traffic congestion; Other cities may pay more attention to the construction and expansion of road networks to improve the accessibility and convenience of urban transportation.

The mean value of external openness is 3.094, the minimum value is 0, and the maximum value is 299.7, indicating that there are obvious differences in the external openness level of Chinese cities. Mainly due to geographical location and regional development differences, cities in China’s coastal areas have unique trading port conditions due to geographical advantages, which is convenient for economic and trade exchanges with the international market. These cities are usually able to absorb international advanced technology and management experience more quickly and promote the development of an export-oriented economy. In contrast, inland cities are relatively closed geographically, not closely connected with the international market, and the degree of openness to the outside world is relatively low. Regional development imbalance: There are significant differences in the level of development between regions in China. The eastern coastal areas have developed economically and improved infrastructure, attracting a large amount of foreign investment and advanced technology. However, the central and western regions and the northeast are relatively backward, and the starting point and foundation of opening up are low, which affects the improvement of the level of opening up.

The mean value of foreign capital dependence is 0.0027, the minimum value is 0, and the maximum value is 0.0473, indicating that there are obvious differences in the foreign capital dependence of Chinese cities. Mainly because there are obvious differences between economic base and industrial structure, economically developed cities usually have better infrastructure and more advanced industrial structure, which can provide a better investment environment and more investment opportunities, so it is easier to attract foreign investment. In addition, the industrial structure of different cities will also affect the degree of foreign capital dependence. For example, some cities are dominated by high-tech industries or service industries, which are easier to attract foreign investment. Some cities dominated by traditional heavy industries may have a relatively low dependence on foreign capital due to the difficulties of industrial transformation and upgrading.

The mean value of government intervention degree is 81.50, the minimum value is 2.010, and the maximum value is 18,700, indicating that there are obvious differences in government intervention degree among Chinese cities. This is mainly because the level of economic development is one of the important factors that determine the degree of government intervention. Economically developed cities, such as Beijing, Shanghai, Guangzhou and other first-tier cities, have higher fiscal revenue and more resources and capabilities to support public services and infrastructure construction, so the degree of government intervention is relatively low. These cities rely more on market mechanisms to regulate economic operations, and the government plays a more regulatory and service role.

The average value of human capital level is 7.189, the minimum value is 0.123, and the maximum value is 11,500, indicating that there are obvious differences in the human capital level of Chinese cities. The main reason is that there are differences in the level of economic development among different regions in China, which directly affects the financial revenue and educational investment capacity of local governments. Economically developed cities such as Beijing and Shanghai can invest more funds in the development of education, including improving the treatment of teachers, improving teaching facilities, optimizing the distribution of educational resources, etc., so as to enhance the level of local human capital.

Table 2 Descriptive statistics results.

Empirical result

Baseline regression

Table 3 reports the baseline regression results of the impact of transport infrastructure construction levels on urban sustainable development. Among them, the results in column (1) report the impact of transport infrastructure construction on urban sustainable development when neither regional effect nor time effect is controlled; the results in column (2) report the impact of transport infrastructure construction on urban sustainable development when regional effect is not controlled but time effect is controlled; and the results in column (3) report the impact of transport infrastructure construction on urban sustainable development when regional effect is not controlled. However, the impact of transport infrastructure construction on urban sustainable development when the time effect is not controlled, the results in column (4) report the impact of transport infrastructure construction on urban sustainable development when the regional effect and time effect are controlled simultaneously. The results show that from column (1) to column (4), the symbol of the estimated coefficient of the transportation infrastructure construction level is positive and passes the 1% significance level test, indicating that the transportation infrastructure construction level can significantly promote urban sustainable development.

Table 3 Basic estimation results.

Robustness test

• (1) Change the way of describing the explained variables. In the benchmark regression analysis, the explained variable economic sustainable development is constructed by constructing an indicator system, using the entropy method to weight each indicator, and then measuring the economic sustainable development index. However, the core of sustainable economic development is economic development. Therefore, this paper further uses regional per capita GDP as an alternative indicator of robustness. The results of the robustness test are shown in Table 4. It can be seen from Table 4 that regardless of whether the regional effect and time effect are controlled or not, and after controlling both the regional effect and the time effect, transportation infrastructure construction still has a significant positive impact on economic sustainable development, which is consistent with the benchmark regression results and proves that this paper The regression results are robust.

• (2) Change the characterization of core explanatory variables. In the baseline regression analysis, the core explanatory variable of this paper is the transportation infrastructure construction described by the total freight volume. Referring to the research of Chen Jie³⁹, The construction of transportation infrastructure can also be characterized by the number of road miles. Therefore, this paper further adopts highway mileage as an alternative index of robustness test, and the robustness test results are shown in Table 4. As can be seen from Table 4, transportation infrastructure construction still has a significant positive impact on urban sustainable development, which once again proves that the regression results in this paper are robust.

• (3) Replace the regression model. Judging from the measurement results of urban sustainable development, there may be model regression bias caused by truncated data in the data. Therefore, with reference to the research of Shen Minghao and Tan Weijie⁴⁰, the estimation method was changed and the Tobit model was adopted to investigate the relationship between transportation infrastructure construction and urban sustainable development again, and the results were shown in Table 4. As can be seen from Table 4, the symbol and significance level of the transportation infrastructure construction estimation coefficient have not changed greatly, indicating that the estimation results in this paper are robust.

Table 4 Robustness test Estimation results (replacement of explanatory variables).

Endogeneity test

Although we will try our best to control the factors that simultaneously affect the construction of transportation infrastructure and the sustainable development of cities, we still cannot completely rule out the problem of missing variables and reverse causality. In this paper, the cross term of topographic relief and year dummy variable is taken as instrumental variable by referring to Zhou Ruibo et al.⁴¹, and the cross term of topographic relief slope and year dummy variable is taken as instrumental variable by referring to Yu Guohua et al.⁴² to solve the endogeneity problem. The test results of instrumental variable method are shown in Table 5. The results show that the impact of transport infrastructure construction on urban sustainable development is consistent with baseline regression.

Table 5 Instrumental variable Estimation results.

Heterogeneity test

City size heterogeneity

The difference of city size is the result of the choice of regional economic strategy under the traditional economic system of China. In order to investigate the possible differential effects of transportation infrastructure construction on city size, this paper conducts a subsample regression based on urban population. Columns (1) and (2) in Table 6 report the heterogeneity of city size of transport infrastructure construction on urban sustainable development. The results show that transport infrastructure construction has a significant positive impact on the sustainable development of large-scale cities, but has no significant impact on the sustainable development of small-scale cities, indicating that the impact of transport infrastructure construction on the sustainable development of large-scale cities is more obvious than that of small-scale cities. The possible reason is that large-scale cities are an important part of talent, technology and capital-intensive industries, while small-scale cities are mostly labor, skill and labor-intensive industries, and the proportion of transportation costs in the investment is smaller than that of large-scale cities.

Regional heterogeneity

There are significant differences in factor investment among different regions. Therefore, the inter-regional flow of factors driven by the improvement of transportation infrastructure construction will change the pattern of resource allocation, and thus have a differentiated impact on regions dominated by different factor input. Columns (3) and (4) in Table 6 report the results of regional heterogeneity of transport infrastructure construction on urban sustainable development. The results show that transport infrastructure construction is significantly positive for the sustainable development of cities in the eastern region and cities in the central and western regions. However, from the perspective of coefficient, the regression coefficient of transport infrastructure construction in the eastern region is 0.0091, which is larger than the regression coefficient of transport infrastructure construction in the central and western regions is 0.0010. It shows that the impact of transportation infrastructure construction on the sustainable development of cities in the eastern region is more obvious. The possible reasons are that city size and capital city are mainly based on capital, technology and talents, and the improvement of transportation infrastructure construction has an effect on sustainable urban development mainly through the influence of market mechanism on technological innovation and employment scale, while resource-based enterprises and old industrial industries dominate in the western Middle East region. In addition to the impact on the resource allocation of such industries through market mechanisms, the improvement of transport infrastructure construction also changes the pattern of technological innovation and employment scale through cost paths, which has an impact on sustainable urban development.

Heterogeneity of financial development degree

As the cornerstone of urban development, transportation infrastructure not only optimizes urban spatial layout, improves economic efficiency, but also significantly promotes the flow and optimal allocation of financial resources. The degree of financial development is significantly different among different cities, and this heterogeneity is more prominent under the influence of transportation infrastructure. This paper conducts sub-sample regression based on the degree of high financial development and the degree of low financial development. The results are shown in columns (5) and (6) of Table 6. The results show that transport infrastructure construction has a significant positive effect on the sustainable development of both regional cities with high financial development and regional cities with low financial development. However, from the perspective of coefficient, the regression coefficient of transport infrastructure construction in regions with high financial development is 0.0015, which is greater than 0.0008 in regions with low financial development. It shows that the transportation infrastructure in the place with high financial degree plays a more significant role in sustainable economic development than that in the place with low financial degree. The main reason is that areas with a high degree of finance tend to have more economic activity and higher demand for transport infrastructure. Good transportation infrastructure can reduce logistics costs and improve transportation efficiency, thus further stimulating economic activities and forming a virtuous circle.

Table 6 Estimation results of heterogeneity test.

Betweenness test

The above analysis confirms that transport infrastructure construction is conducive to promoting urban sustainable development, then through which channels does transport infrastructure construction affect urban sustainable development? As described in the theoretical mechanism analysis, the improvement of technological innovation in the construction of transportation infrastructure is conducive to the adjustment of employment scale.

Columns (1) and (2) of Table 7 show the estimation results of technological innovation. The regression coefficients of the transportation infrastructure construction index are all significantly positive, indicating that transportation infrastructure construction helps promote the level of technological innovation.In addition, the intermediary effect results show that the intermediary proportion of technological innovation is 26.57%.This shows that the positive effect of improving transportation infrastructure on technological innovation is an important way to improve the efficiency of sustainable economic development. This conclusion proves Hypothesis 1.

Columns (3) and (4) of Table 7 present the estimated results of employment scale. The regression coefficients of the transportation infrastructure construction index are all significantly positive, indicating that transportation infrastructure construction helps promote the coordinated agglomeration of employment scale; in the regression of economic sustainable development estimated based on the LP method and the OP method, the transportation infrastructure construction index and The economic sustainable development index is significantly negatively correlated, and the employment scale index is also significantly positively correlated with the economic sustainable development index at the 1% level. In addition, the intermediary effect results show that the intermediary proportion of employment scale is 38.05%. This shows that the positive effect of improving transportation infrastructure on employment scale is an important way to improve the efficiency of sustainable economic development. This conclusion verifies hypothesis 2 and hypothesis 3.

Table 7 Estimation results of mediating variable test.

Conclusion and enlightenment

Based on the urban panel data from 2006 to 2021, this paper empirically examines the impact of transportation infrastructure construction on urban sustainable development and its transmission mechanism. The research results show that: (1) Baseline regression shows that urban transport infrastructure construction can significantly promote urban sustainable development, indicating that urban transport infrastructure construction is an important driving force for urban sustainable development, and this conclusion is still valid after a series of robust recommendations and endogenous treatment. These reasons are as follows:(1) The improvement of transportation infrastructure can greatly improve the accessibility and convenience of the city; (2) A good transportation network helps to optimize the urban spatial layout and promote the rational allocation of resources, especially the technological innovation brought by scientific and technological talents; (3) The construction of transportation infrastructure is often accompanied by a large number of investment and employment opportunities, directly driving economic growth; (4) The improvement of transportation infrastructure can also significantly improve the environmental quality of cities. (2) The results of heterogeneity analysis show that (1) the improvement effect of transportation infrastructure construction on large-scale cities is greater than that of small-scale cities. The possible reason for this is that large-scale cities are an important part of talent, technology and capital-intensive industries, while small-scale cities are dominated by labor, skill and labor-intensive industries. The proportion of transportation cost in the intermediate input is smaller than that of large-scale cities. (2) The improvement effect of transportation infrastructure construction on the central and western regions is greater than that of the eastern regions. The reason for this is that city size and provincial capital cities are dominated by capital, technology and talents. The improvement of transportation infrastructure construction has an effect on urban sustainable development mainly through the impact of market mechanism on technological innovation and employment scale. In addition to influencing the resource allocation of such industries through the market mechanism, the improvement of transportation infrastructure construction also changes the pattern of technological innovation and employment scale through the cost path, thus affecting the sustainable development of cities; (3) Transport infrastructure construction in places with a high degree of finance plays a more obvious role in sustainable urban development than in places with a low degree of finance. The reason for this is that areas with a high degree of finance usually have more frequent economic activities and higher demand for transport infrastructure. Good transportation infrastructure can reduce logistics costs and improve transportation efficiency, thus further stimulating economic activities and forming a virtuous circle. (3) The results of the transmission mechanism show that: (1) The improvement of transportation infrastructure construction promotes urban sustainable development by promoting technological innovation. The reason for this is that transportation hubs significantly promote urban innovative development, which is accompanied by technological progress, thus promoting economic growth and sustainable urban development, and at the same time, it also has significant spatial spillover effects on surrounding areas; The reasons for this are as follows: (2) Transportation infrastructure can enhance entrepreneurial activity, break down household registration barriers, increase the scale of employment, accelerate population migration, improve per capita salary and corporate performance, thereby increasing the share of labor income, affecting the scale of employment, and driving sustainable urban development.

Based on the above research conclusions, this paper puts forward the following policy recommendations:

• (1) Implement transportation infrastructure construction strategies for overall planning of transportation infrastructure construction and overall urban planning (including spatial planning and economic planning). (1) Formulate scientific and reasonable transportation network planning, optimize the layout of railway, road, air, bus and intercity transportation, break the geographical space restriction, promote the flow and optimal allocation of resource elements, and enhance the spatial spillover benefit of urban transportation economy; (2) The use of big data, artificial intelligence, Internet of things and other new generation technologies to give priority to the development of green public transport and intelligent public transport, such as subway, bus, intercity, green bus lanes, electric vehicle charging facilities, low-altitude economy and other transportation infrastructure, improve travel efficiency, reduce traffic congestion, while reducing carbon emissions, promote green travel; (3) Formulate and implement the development concept of “green symbiosis of transportation environment”, and adhere to the principle of ecological priority in the whole process of feasibility study, design, construction, operation and maintenance of transportation infrastructure. Adopt scientific and reasonable implementation strategies of ecological route selection, ecological design, engineering structure, building materials, construction technology, protection and restoration, ecological supplement, soil and water conservation, low noise and low emission, system supervision, public participation and other new technologies, new materials, new processes, and new models to reduce the impact on the ecological environment, and reduce the impact on ecological sensitive areas such as nature reserves. Ensure the harmonious coexistence of traffic lines and ecological environment. By strengthening the construction of transportation infrastructure, the spatial and temporal distance between cities can be shortened, the green symbiosis mode of transportation environment can be created, the economic ties, cooperation level and symbiosis level between regions can be improved, and the coordination between transportation infrastructure and urban development planning can be promoted to inject new vitality into the sustainable development of cities.

• (2) Implement differentiated transportation infrastructure construction strategies for cities of different sizes: (1) Large-scale cities should give priority to the development of public transportation systems, such as subways, light rail, etc., to alleviate traffic congestion and improve citizens’ travel efficiency. At the same time, it will promote the construction of intelligent transportation systems and use big data to optimize traffic flow management and reduce traffic delays. (2) For small-scale cities, more attention should be paid to the improvement and upgrading of transportation infrastructure, such as adding bus routes and improving road quality to meet basic travel needs. However, in view of limited resources, blind pursuit of large-scale transportation projects should be avoided to avoid wasting resources. (3) The government should establish a regional coordination mechanism for the construction of transportation infrastructure to ensure smooth traffic connections between large-scale cities and small-scale cities and promote the integrated development of regional economy.

• (3) Implement transportation infrastructure construction strategies for cities in different regions to narrow differences: (1) Increase investment in transportation infrastructure in the central and western regions, especially the construction of high-speed railways, expressways and aviation networks, so as to accelerate economic exchanges and resource flow between regions and narrow the gap with the eastern region. (2) Promote the application of intelligent transportation systems in the central and western regions, use scientific and technological means to improve traffic operation efficiency, reduce logistics costs, and provide strong support for local industrial upgrading. (3) Pay attention to the construction of transportation hub cities in the central and western regions, enhance its radiation and driving role in regional economic development, and form a new economic growth pole. (4) Strengthen the transportation interconnection between the eastern and western regions, build a more complete national transportation network, and promote the coordinated development of regions. By optimizing the construction of transportation infrastructure, it will provide a strong guarantee for the economic rise of the central and western regions.

• (4) Implement city-specific transportation infrastructure construction strategies for cities with different financial levels: (1) In areas with high financial levels, priority should be given to investing funds in modern transportation infrastructure construction such as intelligent transportation systems, high-speed railways and green transportation networks to efficiently connect inside and outside the city, promote the flow of capital, talent and information, and accelerate the transformation and upgrading of urban economy. (2) In areas with low financial degree, financial institutions should be encouraged to participate in transport infrastructure projects, and social capital investment should be attracted through innovative financing models, such as PPP (public-private partnership), to improve the sustainability and efficiency of transport infrastructure construction. (3) Use financial resources to promote the green transformation of transportation infrastructure, such as the promotion of electric vehicle charging stations, green public transport systems, etc., to reduce carbon emissions and improve urban environmental quality.

• (5) For transportation infrastructure construction, implement transportation technology industry bundling transportation infrastructure construction strategies by promoting technological innovation to promote sustainable urban development: (1) Increase investment in technological innovation in the field of transportation infrastructure, especially in intelligent transportation systems, green transportation technologies and new energy transportation equipment, encourage enterprises, universities and research institutions to carry out joint research and development, and accelerate the application and transformation of technological innovation results.(2) Establish transport infrastructure technology innovation demonstration zones and pilot zones, provide policy support and experimental platforms for the landing of new technologies and new models, attract more innovation resources to gather, and form a virtuous cycle of technological innovation and industrial upgrading. (3) Strengthen the integration and development of transportation infrastructure construction with other areas of the city, such as deep integration with smart cities, digital economy and other fields, promote the modernization of urban governance system and governance capacity, and enhance the city’s comprehensive competitiveness and sustainable development level.

• (6) To promote sustainable urban development by influencing the scale of employment in the construction of transportation infrastructure, implement the strategy of transportation employment-driven transportation infrastructure construction: (1) The government should increase investment in the construction of transportation infrastructure to create more job opportunities. For example, investment in the construction and maintenance of projects such as subways, buses, highways and ports will directly promote the development of related industries such as construction, equipment manufacturing and logistics, thereby increasing jobs. (2) Governments should encourage and support localized employment in transport infrastructure projects. In the process of project implementation, priority will be given to local labor, through training and upgrading skills, so that local residents can be competent for relevant jobs and reduce the dependence on foreign labor. (3) The government should formulate relevant policies to promote the coordinated development of transportation infrastructure construction and other urban industries. For example, through the construction of transportation hubs and logistics centers, more enterprises can be attracted to settle in, forming industrial clusters and driving employment migration, thus further promoting urban economic development and employment growth.