Along with rapid economic development in China, people’s living standards are gradually increasing, and the number of private cars is increasing daily. While enjoying the convenience brought by cars, people must also face the resultant traffic jams, parking difficulties, environmental pollution, and other social issues. Currently, the number of motor vehicles in first-tier and second-tier cities continues to increase, and the demand for parking is constantly expanding. Constructing infrastructure for parking lots in major cities lags behind the development of cars, and, consequently, the demand for parking management cannot keep up. As such, “disorderly parking” has intensified, seriously affecting the urban environment and traffic order. It has become urgent need to solve the problem of parking in urban areas, especially in city centers.

Underground parking can take full advantage of underground space, which provides a practical solution to the current parking problems. However, because of problems pertaining to parking and collecting cars, the high cost of parking, and lack of combination between static traffic and dynamic traffic, many underground parking lots are empty in some areas at specific times. Many key issues must be solved to promote underground parking lots in China. Therefore, this paper studies the necessity and urgency of the construction of underground parking lots, as well the planning and design, operation, and investment and financing thereof to contribute toward solving problems pertaining to urban traffic congestion and the planning and construction of urban underground parking lots.

An investigation and analysis of the city parking system in China revealed the following five major problems.

2.1.1 Large gaps between parking space supply and demand

As China’s social economy continues to develop, the number of those owning cars is rapidly growing. As shown in Fig. 1, as of the end of March 2017, car ownership in the country totaled 200 million, and exceeded 1 million in 49 cities across the country. Furthermore, 19 cities have more than 2 million vehicles, of which 3 million are registered and filed in six cities, namely Beijing, Chengdu, Chongqing, Shanghai, Suzhou, and Shenzhen. The average annual growth rate of car ownership in some cities exceeds 20%.

In recent years, the number of parking facilities has steadily increased; however, there is still a shortage of parking space compared to the rapid expansion of parking demand [1]. For example, by March 2017, the number of vehicles in Beijing totaled 5.54 million, while there were only 1.9614 million parking places, about one third of the total vehicle ownership (Fig. 2). According to the experiences of domestic and foreign cities, each car in the city should have 1.2–1.3 parking spaces. According to conservative estimates of a ratio of 1∶1 cars and parking spaces, the gap between the supply of and demand for parking spaces in Beijing is 3.58 million. According to the data released by the National Development and Reform Commission, the average proportion of cars and parking places in China’s big cities is about 1∶0.8, and around 1∶0.5 in small and medium-sized cities [2]. As a standard, a gap is evident between the supply of and demand for parking spaces in most cities in China, substantiating the urgency of constructing underground parking lots.

2.1.2 Unreasonable parking space and a serious shortage of parking facilities

In traffic engineering, three types of parking lots are identified: the parking lots of public buildings, outside parking lots, and roadside parking lots. A ratio of 6∶2∶2 of the three types indicates a reasonable parking structure [3], although this ratio in many cities in China is 1∶5∶4. Thus, the parking lots of public buildings, which can play a leading role, theoretically only play a supplementary role.

2.1.3 Side parking

According to the survey and statistics, side parking is common in many cities in China. Side parking occupies sidewalks and non-motorized lanes, affecting the capacity of the road,which can easily lead to many problems such as traffic disorder and traffic accidents [1].

2.1.4 Unreasonable planning and design of existing parking lots

The unbalanced layout of and demand for public parking facilities, uneven distribution of parking facilities, and inaccurate forecasting of parking demand means that some parking lots face the problems of low utilization and poor operating conditions, despite severely limited parking spaces in China. In addition, the form of the planned and designed parking lots is monotonous, and most are ground parking lots. Mechanical parking lots with high space utilization and high efficiency are used less often [1].

2.1.5 Residents are not strongly law abiding

Illegal parking by residents who do not abide by the law is also one reason for parking problems [4]. Because of the shortage of parking resources, many people park directly on the roadside, which affects traffic and negatively impacts the urban environment. However, the penalty for illegal parking in China is extremely low, which condones and intensifies parking difficulties.

In view of the parking problems, relevant policies for parking lots have been launched at all levels of the country, aiming to guide and coordinate various aspects including funding, planning, and construction to promote the development of parking lots.

In 2015, the National Development and Reform Commission, Ministry of Finance, Ministry of Land and Resources, and four other ministries issued the Guiding Opinions on Strengthening the Construction of Urban Parking Facilities (hereinafter referred to as Opinions). It calls for fully mobilizing social capital, accelerating the construction of parking facilities, and effectively alleviating the shortage of parking space [5]. The 13th FiveYear Plan for Urban Underground Space Development and Utilization also proposed the development of underground parking requirements. At present, 18 cities nationwide have promulgated 31 laws and regulations relating to the construction of parking lots, including the aspects of land allocation and transfer, commercial facilities up to 50 %, tax relief, property tax exemption or land-use tax exemption, incentive subsidies, and charging the market regulation price.

Many cities have promulgated local regulations and policies that encourage the construction of public parking lots and guide private capital investment in these. However, the effect of promoting underground parking lots has not been significant for the following reasons. ① Although local governments have promulgated various policies, these have not been implemented, as policy support is still in the text stage. ② Although good conditions have been provided for building parking lots, support remains insufficient, making the cost of building underground parking lots too high. Thus, the expected return of investment cannot attract private capital. ③ Policies and regulations for parking lots are interlaced. In the process of engineering construction, many problems will emerge, such as multi-management and repeated auditing, which will affect the efficiency and enthusiasm of parking lot construction. Therefore, many key problems must be solved to popularize underground parking lots in China.

To solve the problem of irregular parking on the pavement and improve the capacity of roads and traffic conditions, many countries have adopted various policies and measures to strengthen the construction and management of parking lots. Currently, relatively perfect parking lot rules and an independent management system have been formed.

Because of its huge population, heavy traffic, and poor road conditions, Japan has been promoting vehicle parking construction and parking management through policy guidance, legal management, and technological innovation since the 1950s. Its main measures include the following three aspects.

3.1.1 Formulating relevant preferential policies to promote the construction of parking lots

① The main bodies overseeing parking lot construction are non-government institutions, who financially subsidize private and semi-private parking lots and encourage private capital investment in the construction thereof. ② The country provides low-interest loans for the construction of parking lots through road development funds, special interest rate financing by banks, and NTT stock sales revenue. ③ Different tax relief regulations for taxes pertaining to the construction of parking lots [6], such as construction tax and enterprise income tax, have been introduced.

3.1.2 A law standardizes the construction and management of parking lots

As shown in Table 1, the laws and regulations pertaining to parking lot construction in Japan are effective, comprehensive, and detailed, covering the entire contents of parking lot construction and parking management. In addition, these were introduced earlier and revised to ensure the standardization and orderliness of parking lot construction and management [6].

3.1.3 Development of underground parking lots based on local conditions

① Japan advocates the promotion of three-dimensional mechanical garages, and was one of the earliest countries to adopt these. In the early 1960s, Japan developed and used a mechanical parking lot that maximized the use of space. By the end of 2014, the country housed 2.96 million mechanical parking spaces. ② Furthermore, Japan actively advocates the principle of “small but decentralized,” and encourages operators to make rational use of space to build small-scale parking lots. Some parking lots have only two or three parking spaces with flexible and convenient signage. ③ The country provides a comprehensive parking guide and parking guidance system to reduce unnecessary road exploration and roadside parking and to improve the efficiency of existing parking lots [7].

With the growth of traffic quantity, parking and related problems are becoming increasingly severe. Many European countries and the United States have adopted various parking policies to improve parking problems. These policies and measures involve urban planning and the rationalization of urban traffic structure [8]. The typical experience is as follows.

3.2.1 Increase parking lot capacity and reduce the gap between supply and demand

In the early stage of parking lot construction, European cities created conditions for short-term parking by placing temporary parking boards on streets. However, they later found that this method reduced the patency of the roads, and many countries canceled these measures [8]. In the middle and late stages of parking lot construction, major cities adapted to the growing parking demand by building three-dimensional and mechanized parking lots [9].

3.2.2 Perfect the laws and clarify the obligations of parking lot builders

Some cities in the United States require that enterprises within the service area of new parking lots and real estate owners bear part of the cost of parking construction to promote the construction of parking lots in the area [3].

3.2.3 Strengthen the management of parking lots

Britain has the most sophisticated parking management system in the world, and is one of the most successful countries in this regard worldwide. The Greater London Council (GLC), which is granted by the UK, has the mandatory right to curb traffic volume by controlling parking lots in the central part of the city where traffic is increasing to promote the use of public transport. The main approaches include the following. ① Different parking time limits are set in different areas and the efficient operation of the parking spaces network is ensured by adopting a time-accumulated rate (charging higher fees for long-term parking users) and strictly enforcing the law [9]. ② The country enhances the management of non-public parking lots by setting an upper limit on the size of the parking lots of public buildings, mobilizing the owners of private parking lots to open their spaces to the public, and taxing private parking lots to transform them into public parking lots.

3.2.4 Readjusting the urban traffic structure by implementing a new parking policy

In the mid-term of motorization, the development of parking facilities in urban centers has shifted from the construction stage to the improvement stage of intensive management. As a subsystem of the transportation system, parking lots are not only a problem of static traffic supply, but also an important means of “to treat dynamic traffic with static traffic.” The parking policy is gradually being used as part of the urban planning and transportation policy to promote the adjustment of the urban traffic structure [9,10]. The main approaches are as follows: ① limiting roadside parking through compensated use to improve road traffic capacity, ② separating humans and cars by creating pedestrian streets and parking on the fringe area to control the traffic flow in the city center [9], and ③ building a park-and-ride (P&R) parking lot to transfer vehicle traffic demand to public transport modes and adjusting urban traffic structure [8,9].

Singapore is a highly developed country. Its land area is small and population density is high. However, no serious parking problems are evident. The solution to the parking problem stems from the two aspects of supply and demand.

3.3.1 The supply side

① In densely populated urban areas, an advanced and intelligent parking network is used to develop a three-dimensional parking system to ensure that the capacity of public parking lots meets the demand. ② The policy of “rent only and do not sell” is implemented in parking lots. There is no single fixed parking place in public residential buildings, private apartment buildings, and commercial service areas. Parking is based on a “first come, first park, and park at any time” basis to improve the utilization efficiency of parking lots [6].

3.3.2 The demand side

The government of Singapore does not encourage people to buy a car, as the annual cost of road maintenance totals tens of thousands yuan. This means that people can afford a car, but cannot afford to use it. Thus, the number of car owners is low, which controls the demand for parking from the source thereof.

A large number of underground parking lots must be constructed; therefore, a large amount of funds is needed for construction. Furthermore, the construction of parking lots should be combined with the characteristics of the city and different parking construction projects should adopt different modes. Currently, there are three modes by which to construct underground parking lots in domestic and foreign cities, including government investment, joint investment between government and the private sector, and private investment under government control. The main financing modes for parking lots constructed jointly by the government and private sector or owned by the private sector include build-operate-transfer (BOT), build-transfer (BT),transfer-operate-transfer (TOT), transfer-build-transfer (TBT), and government and social capital cooperation.

In general, the public-private partnership (PPP) model is suitable for building non-profit parking facilities. It can attract public investors in accordance with the mode of public-private cooperation. The franchise period does not generally exceed 30 years, and the internal rate of return is usually less than 8 %. The government provides support if the actual income is lower than the target income. Other business parking lots can be constructed in a market-oriented way, and encourage investment in the construction and operation of parking lots through public-private partnerships using BOT or BT. The operation process for PPP projects regarding parking lots is illustrated in the PPP parking lot project in Luzhou city of China. As shown in Fig. 3, after determining the social capital procured, the project company completes a preliminary examination and approval procedures, as well as a survey and the design, construction, and other work required in the project. After completing project construction and acceptance thereof, the project company charges and manages the parking lot in accordance with the relevant regulations, and is responsible for its hygiene and maintenance, as well as for repairing the structure of the main components when needed. After 30 years of the project franchise, the project company transfers the project assets to project implementation agencies without compensation, and cancels its liquidation, after which the cooperation for the project is terminated.

In the process of building an underground parking lot, obtaining construction land is a key issue. It is necessary to consider the following situations. ① The construction of a new project should match the underground parking lot. The land and property rights should be divided according to the nature of the new project. Furthermore, there is no additional land transfer fee. ② The nature of the expanded underground parking lot is determined by the nature of the established project, and the land for the underground parking lot is obtained through a transfer, the same as for the main body. ③ The newly constructed public parking lots dominated by the government requires that local governments coordinate the purchase of land by local authorities, financial allocations, and investment by local state-owned companies. Newly constructed parking lots that employed the PPP model can attract social investors to participate based on “the government providing the land and the market the funds.” ④ In general, land is acquired for the construction of underground parking lots through bidding, auctions, listings, and other means.

In terms of managing a parking lot, it is recommended to develop intelligent underground mechanical parking lots that consist of a unified code of parking space, vehicle geomagnetic sensors, intelligent vehicle terminals, Beidou high-precision ground enhanced positioning technology, wireless intelligent parking management terminals, a smart parking management system, automatic recognition system for vehicle licenses, user-oriented mobile apps, and other related high tech. With the establishment of intelligent underground mechanical parking lots, basic information, management information, and operational information on these lots (bits) can be summarized. Then, through the Internet, Internet of Things, big data, and other networking technologies, an intelligent parking management service platform can be established to be used to interconnect city-level parking lots and unify vehicle management, intelligent supervision and control, electronic payments, and car-related data sharing [5]. In the prevailing situation of the “Internet Plus” initiative, the promotion of intelligence and information management for parking lots uses Internet thinking to carry out management upgrades and change the profit model of the traditional parking industry, which can effectively increase the efficiency of the use of parking resources to relieve the problem of parking in cities.

In terms of parking management, it is recommended that a limited-time parking system be implemented. This entails charging for parking according to time, increasing the extent of punishment for parking violations, and limiting on-street parking. The implementation of these systems may result in some car owners switching to public transport, which will reduce the demand for parking lots accordingly. Large cities must prohibit parking on roads with heavy traffic. Compared to foreign countries, there is a large gap in terms of the implementation of regulations, strict punishment, and the refinement and fairness of terms. It is suggested that the government should escalate the parking issue to the legislative management level as soon as possible to ensure the rational use of parking resources.

There are many classifications for underground parking lots. According to different service groups, underground parking lots can be public or special types, or single-built and side-by-side according to the positional relationship with ground buildings. Based on different usage methods, they can be classified as ramp or mechanical types, or according to the size of the parking and requirements for fire prevention [7].

Among the types of urban underground parking lots, a mechanical underground garage demonstrates a high degree of automation and land use, and provides many advantages, such as a flexible layout and large parking density. Therefore, it provides a new direction for the development of urban parking facilities. There are different forms of underground mechanical parking lots. The main types are vertical lifting, circulating parking spaces, aisle-stacks, and lift-sliding [7], as shown in Fig. 5. Because of the different equipment used, this type can be categorized as a horizontal circulating mechanical parking system or multi-layer circulating mechanical parking system.

This type of parking lot uses stacker cranes and other mechanical equipment to drive the vehicle to perform horizontal and vertical movements on dedicated passages and transport the vehicles to parking spaces, entrances, or exits. This type of parking lot needs space for the stacker cranes to run inside. Though there is lower utilization of space than in other circulating mechanical parking systems, its operating speed is faster [7]. The structure of the lift-sliding mechanical parking system is simpler than the others and can take a modular design. Its advantages include high cost performance, strong adaptability, mature technology, and high reliability. It is the most used type of underground mechanical parking lot in China, and is shown in Fig. 7.

When selecting the type of underground mechanical parking lot, factors such as vehicle size, parking lot capacity, service radius, management, and charges should be considered. The most appropriate type of parking lot should be selected according to the principles of appropriateness, reliability, and humanity. When the underground space is relatively large, an aisle-stack mechanical parking system and lift-sliding mechanical parking system can be adopted. When the underground space is deep and narrow, a vertical lifting underground mechanical parking lot can be adopted. When one direction of the underground space is long and the other side narrow, it is best to opt for a horizontal circulating mechanical parking system. Finally, when an ordinary parking lot is mechanically transformed, a mini mechanical parking system should be selected [7]. The space design of the column grid should consider the spacing of the mechanical structure, size of the vehicle, and combination of structures to maximize space utilization. Section design considers the net height of the vehicle and mode of mechanical operation. As shown in Fig. 11, the basic reference size of a single parking space is 5.05 m × 1.85 m × 1.55 m (length × width × height). The design of the entrance and exit of an underground mechanical parking lot incorporates lifters to increase the efficiency of accessing vehicles. Attention should be paid to coordination with the surrounding environment. The dimensions of the entrance and exit should meet the following requirements. The width should be more than 0.5 m greater than the maximum width of the transported vehicles and the total width should be at least 2.25 m. The height should be more than 1.8 m, and the total height at least 0.1 m more than the height of the parked vehicles [7].

Underground parking lot construction technology is essentially a deep foundation pit created through open cut, cover-cut, or open caisson methods. Table 2 outlines the specific application conditions.

Selecting a method by which to construct retaining structures is based on the characteristics of the project and geological conditions. Underground diaphragm walls are suitable for foundation pits with high deformation and waterproof requirements, and can be used as part of the main structure; however, the cost is high. The cost of bored pile is relatively low and has high rigidity, making it suitable for the construction of deep foundation pits.

The cylindrical underground parking lot is relevant here, because of its small footprint, wide applicable range, and high space utilization. The underground structure of this type of parking lot is similar to a shaft structure. Therefore, the following shaft construction method can also be used. ① If the conditions of the stratum are suitable, and the site is open, an ordinary drilling and blasting method can be used to excavate the shaft. ② If the depth of the shaft is large and the construction site conditions are appropriate, mechanical drilling can be used. This method can prefabricate the borehole wall while excavating, improve the quality of construction, and shorten the period of construction. ③ When unstable geological conditions are evident such as high moisture content and the existence of mucky soil and quicksand, the freezing method can be used, which means using artificial freezing technology to freeze the rock mass around the shaft before excavating it.

With the continuous development of underground engineering, new methods or improved technologies are emerging. ① Sphere shield construction technology. The sphere shield can complete the excavation of a vertical foundation pit and be turned in the shaft to directly excavate the underground space required for the parking lot. The advantages of this technology are its small environmental impact, high structural stability, and ability to save on workload. ② “Pile-wall combination” technology. As shown in Fig. 12, this method combines the technology of secant piles, underground diagram walls, and open caisson, and integrates the retaining and waterproofing functions of the enclosure structure to form a “three-in-one wall” structure. This new technology is significant in saving energy and reducing consumption, and contributes to the sustainable development of foundation pit supports. As such, it can be well utilized in the construction of underground parking lots.

(1) In the process of developing urban underground parking lots, efficiency, safety precautions, and the management of existing parking lots should be improved

Through the coordination of urban dynamic and static traffic, rational guidance of regional traffic flow, and improvement of urban planning, the utilization rate of existing parking lots will be increased. By using the Internet, Internet of Things, and other technologies, an intelligent parking management system can be developed. Through intelligent booking, intelligent parking guidance, intelligent identification, and other functions, the intensive management and security of parking lots can be improved. According to information obtained from big data such as regional parking demand and urban traffic development, the layout of cities will be optimized and city development promoted scientifically, efficiently, and healthily.

(2) Flexible handling of construction management and investment and financing modes

The construction and management of parking lots are based on the diversification of construction, management of localization, and intelligentization of facilities, and achieved through co-ordination, integration, and intensiveness. We must use various means including legal, administrative, technological, and financial aspects, and adhere to the combination of government guidance and market leadership.

(3) According to needs related to parking, underground parking lots should be planned and designed based on local conditions

Planning for underground parking lots should consider space characteristics and urban layout. Currently, underground mechanical parking lots provide many advantages such as a small footprint, flexible structure, high degree of automation, safety, and reliability, which should be prioritized in the construction or renovation of urban parking lots.

(4) When developing urban underground parking lots, suitable construction methods can promote the development of the parking industry

Construction methods such as open-cutting and undercutting should be selected according to the engineering environment. Furthermore, rapid construction and prefabricated structural assembly construction technologies should be developed, and the supporting facilities, mechanical structures, and control systems of underground parking lots unified. Ultimately, a complete industrial chain will be formed, the efficiency of parking lot construction increased, and the industrialization of parking lots and development of the urban economy promoted.