Carbon-Reduction Requirements in Linear Transport Infrastructure Construction Contracts: An Analytical Review and a Contractual Readiness Framework

Carbon reduction in linear transport infrastructure cannot be achieved merely by setting environmental targets or incorporating carbon-related criteria into tender documents; rather, it requires translating these objectives into clear, measurable, and verifiable contractual obligations. This study adopts an analytical review approach to synthesize technical, procurement, contractual, and professional evidence related to road, highway, pavement, bridge, tunnel, railway, and metro projects, and examines the pathway through which carbon policy is converted into implementation outcomes. The findings indicate that the measurability and contractual manageability of carbon-reduction requirements depend on the clear definition of the system boundary, baseline, functional unit, calculation method, data requirements, responsibilities, change-control procedures, and verification mechanisms. Based on the reviewed evidence, carbon-reduction requirements were classified into seven categories: disclosure and information requirements; management and process requirements; prescriptive technical requirements; performance-based requirements; measurement, reporting, and verification requirements; change-control, risk-allocation, and flow-down requirements; and commercial consequences and enforcement requirements. A framework was also developed to assess the contractual readiness of these requirements. The results further show that Environmental Product Declarations, carbon-management plans, and tender criteria alone do not ensure actual carbon reduction; instead, they must be embedded within an integrated chain extending from procurement and contract formation to implementation, final verification, and commercial decision-making. A major limitation of the existing body of knowledge is the scarcity of empirical evidence that tracks carbon requirements throughout the complete contractual lifecycle, particularly in railway and metro projects.