1. Introduction
The existing research on the coupling of urban transportation networks and power grids will realize the intellectualization and low-carbon use of urban transportation energy supply, and improve the operation efficiency and environmental protection of transportation networks and power grids [
1,
2,
3]. In this context, actively using carbon trading and other market means to control emissions is more conducive to creating low-carbon transportation and a green environment [
4,
5]. In recent years, the core of low-carbon transportation characterized by low energy consumption, low pollution and low emissions has been to optimize the development mode of transportation and improve its energy efficiency and energy-consumption structure. As a key focus area of the transport industry, urban public transport has the characteristics of high efficiency, high energy consumption, high traffic volume and regular operation [
6,
7]. Therefore, how to reduce the emissions and operating costs of urban public transportation without affecting its transportation capacity by means of the carbon-trading market is the issue studied in this paper.
Urban public transport can buy and sell carbon emissions in the carbon-trading market, and urban public transport enterprises can obtain carbon-trading income and reduce carbon emissions [
8,
9]. China’s Beijing Public Transport Group, which was included in the carbon-market management in 2016, has reduced its carbon-emission intensity by more than 11 percent in 2020 compared to 2016 due to the aggressive investment in renewable energy vehicles to replace high-carbon-emission diesel vehicles. Therefore, the participation of urban public transport in carbon trading is conducive to the realization of the “carbon peak” goal of the transport industry. Urban public transport has become the key subject of carbon trading in China’s transportation industry [
10,
11,
12]. As an emerging distributed ledger technology, blockchain has also been widely studied in the field of carbon trading [
13,
14,
15]. Therefore, it is of great significance to combine urban public transport, carbon-trading systems and blockchain.
In order to effectively improve the operation efficiency and emission reduction capacity of urban public transport in the carbon-trading market, most contemporary studies seek favorable methods or approaches in terms of fuel cells, fuel economy, carbon tax and carbon-trading relationships, renewable-energy-vehicle subsidy policies, carbon-quota policies, etc. [
16,
17,
18]. At present, China’s carbon-trading market has been established for a relatively short time, and the research on urban public transport participation in carbon trading is in the theoretical stage and less research has been conducted in this regard. Reference [
19] analyzed the fuel cell market in the field of urban public transport in China, studied the impact of carbon trading on the cost of hydrogen fuel cells and showed that the carbon-trading model can effectively reduce the cost of fuel cells. Ref. [
20] proposes a real-time predictive energy-management strategy (PEMS) of plug-in hybrid electric vehicles for the coordination control of fuel economy and battery lifetime, and a model predictive-control problem of cost minimization, including fuel-consumption cost, electricity cost of battery charging/discharging and equivalent cost of battery degradation, was formulated. The authors of [
21] studied and simulated the carbon-quota allocation of road public transport, introduced the idea of baseline incentive allocation on the basis of the data envelopment analysis (DEA) model, and proposed a new method of analysis from the perspective of vehicle carbon-emission intensity. Reference [
22] re-analyzed the difference between the implementation of carbon tax and carbon-trading policies, including the public transport industry, by using the recursive dynamic computable general equilibrium model. The authors of [
23] built a multilevel supply chain for the production, sales and parts recycling of new-energy vehicles, and established a Stackelberg game model led by new-energy-vehicle manufacturers. Based on this, they discuss how to coordinate enterprise production income and urban public transport vehicle emission optimization under the carbon-trading system. The authors of [
24] use a multiregional multisector computable general equilibrium (CGE) model with two simultaneous international emission-permit markets, including road transport. The authors of [
25] presented an agent-based modeling approach for personal carbon trading and addressed questions on the price and reduction rate of allowances.
The above documents have certain reference significance for urban public transport to participate in the carbon-trading market, but there are also some problems: the security of carbon-trading-related data has not been considered; the efficiency of information transmission is low due to centralized management [
26,
27]; the incentive effect of promoting urban public transport to participate in carbon trading and emission reduction is not obvious [
28,
29] and asymmetric and imperfect transaction matching information between urban public transport transaction entities leads to few overall benefits [
30,
31,
32].
The application of emerging technology blockchain in the carbon-trading mode is expected to become a new way to solve the above problems. The blockchain system uses the distributed consensus mechanism to generate and update data. Its characteristics, such as decentralization, point-to-point transactions and full-node participation in data recording [
33,
34,
35], have eliminated the possibility of illegal data compilation from the technical level, and improved the traceability of carbon emissions from mobile sources of urban public transport. Refs. [
36,
37] proposed a personal carbon-credit-trading model and established a carbon-emission-right verification system for the blockchain. Reference [
38] used the multistandard analysis method to evaluate the proposed government transport individual trinity carbon-trading system co-governance policy based on blockchain technology. The authors of [
39] summarized the existing achievements of blockchain application in the field of carbon trading, designed the blue carbon system architecture diagram under peer-to and enriched and promoted the development of the current carbon-trading market. The authors of [
40] established a carbon-emission-trading-mechanism model based on blockchain, taking into account the credibility of both parties. The study in [
41] provides a blockchain-based energy-trading network, and it significantly reduces carbon footprint (15%) by enhancing energy exchange between intelligent agents. The above studies all use blockchain to establish a new carbon-trading system.
To sum up, the existing research at home and abroad mainly focuses on how the public transport industry can effectively enter the carbon-trading system and apply blockchain technology to the carbon-trading system [
42]. Based on the characteristics of blockchain technology and considering the actual business scenario requirements, this paper designs a framework for urban public transport to participate in the carbon-trading system, and establishes the emission reduction progress factor index considering profits, passenger flow and carbon emissions, and then establishes the urban public transport operation-cost model and transaction-matching model under the carbon-trading scenario. The practical significance of this paper is to reduce carbon emissions and operating costs of urban public transportation by optimizing transportation operation strategies and facilitating carbon-trading matching between buyers and sellers through the proposed model. This provides a reference for further carbon-market-based management of urban public transportation in the future, and also provides a theoretical model for urban public transportation enterprises participating in carbon trading.
5. Conclusions
Based on the security, decentralization and smart contract features of blockchain technology, this paper establishes a system model for urban public transportation networks to participate in carbon trading. In order to improve the enthusiasm and operational efficiency of urban public transportation to participate in the carbon-trading market, and at the same time reduce the operational cost and carbon emission of urban public transportation, the operational cost model and carbon-trading-matching model are established, and through the analysis of arithmetic examples, the results show that.
The proposed system model for urban public transportation networks to participate in carbon trading leverages the decentralized, distributed ledger and smart contract technologies of blockchain. Hyperledger Fabric was used as the simulation platform, and all the urban public transportation enterprises on the chain were used as user nodes for carbon trading. To a certain extent, this ensures the security and traceability of the data of the chained urban public transport enterprises and improves the operational efficiency of the carbon-trading market.
The urban public transportation operation-cost model established in this paper takes into account the realistic characteristics of urban public transportation. The passenger volume, carbon emission and profit were selected as the basis of the proposed emission-reduction progress factor index, and the genetic algorithm was compiled into the blockchain to solve this model. The results show that the total operating cost and carbon emission of the optimized urban public transportation are reduced.
In this paper, a matching model for urban public transportation carbon transactions was established and the Hungarian algorithm was compiled into the blockchain. By matching the satisfaction of both sides of the transaction, the aggregated transaction between the uplinked urban public transportation enterprises is realized. The carbon-trading efficiency and market activity are improved.
This paper provides a preliminary exploration into and research on the construction of urban public transportation participation in the carbon-trading mechanism, realizes the carbon-market-based management mode of urban public transportation, provides reference for urban public transportation enterprises to reduce emissions and contributes to the realization of low-carbon transportation. In addition, there is still room for improvement in the specific market mechanism design and different types of urban public transport participation in carbon-trading behavior. The limitation of this paper is that the selection of urban public transportation models is relatively single, and only representative indicators were selected, which still lacks comprehensiveness. Further refinement and in-depth research on the coordination of interests among urban public transportation and the selection of calculation model indicators are needed in the follow-up.