## 1 Introduction  
It is reported by Intergovernmental Panel on Climate Change (IPCC) statistics that the construction industry consumes 40% of the world's energy and produces 36% of global greenhouse gases [1]. The greenhouse gas emissions of the construction industry are far higher than those of the transportation and industrial sectors. Bridges are a resource- and energy-consuming infrastructure with the characteristics of high energy consumption, high carbon emissions and high resource consumption throughout their life cycle and are a massive source of CO\({}_{2}\) emissions in the construction industry [2]. In the past decade, the average annual rate of highway bridge construction in China has been 27,000 per year. By the end of 2021, there were 961,100 highway bridges nationwide, an increase of 48,300 over the end of the previous year; among them, there were 7417 extra-large bridges, 134,500 bridges, and nearly 820,000 medium and small bridges [3]. Thus, bridge construction in China is developing rapidly. At the same time, energy consumption is growing rapidly, greenhouse gas emissions are rising sharply, and the scale of bridge construction projects has caused major damage to the environment. Therefore, it is urgent to quantify the carbon emissions in the bridge construction stage and then monetize the carbon emissions, that is, to convert the external impact of carbon emissions into direct economic losses within the enterprise, to encourage the enterprise to take carbon emission reduction measures consciously.  
Carbon emissions need to be monetized through a certain carbon pricing mechanism. Currently, there are two mainstream carbon pricing mechanisms--carbon tax and carbon trading. Carbon taxes refer to the government setting tax rates for greenhouse gas emissions, which are uniformly converted into carbon emissions to obtain direct taxes [4]. [PERSON] and [PERSON] [5] believe that environmental taxes can act as economic incentives to encourage companies to innovate and seek production methods that are economical and have little impact on the environment. In addition, [PERSON] and [PERSON] [6] believe that the implementation of carbon emissions trading policies in countries around the world can effectively reduce global carbon dioxide emissions. [PERSON] et al. [7] believe that carbon emissions trading can encourage companies to use environmentally friendly technologies and innovations, thereby reducing carbon emissions. Implementing a carbon pricing mechanism will make greenhouse gas emissions a cost for enterprises. Enterprises can choose different resource inputs or products according to their own conditions to control greenhouse gas emissions, thereby curbing global warming.  
The aims of this study are as follows. First, a carbon cost calculation model for bridge construction based on carbon trading and the carbon tax system is proposed. By quantifying the direct economic losses caused by carbon emissions, companies are encouraged to choose different resource inputs or products to control carbon emissions according to their own conditions. Second, taking an actual bridge in Beijing as an example, we comprehensively analyze the carbon emissions and carbon costs of the bridge construction stage, clarify the key stages of carbon emission control in the bridge construction stage, and help companies focus on the high carbon emission stage to formulate carbon emission reduction strategies.