Profiles of the focus group participants.

Unforeseen additional costs are major sources of cost overruns for the UK’s highway projects. General contractors normally allocate cost contingencies in their tender prices to cover these costs, primarily based on the judgements of their cost estimators. However, cost contingencies allocated to the same risk by different cost estimators can vary significantly. Although objective factors influencing the estimation of cost contingencies have been extensively investigated, subjective factors remain underexplored. Therefore, this paper aims to address this gap by investigating the subjective factors influencing cost estimators’ judgements through a qualitative study. Twelve semi-structured interviews were conducted with experienced cost estimators working for general contractors in the UK’s construction industry. A follow-up focus group study was also conducted with seven experienced cost estimators in the UK’s construction industry to validate the interview results. The findings reveal that there are thirteen influencing factors affecting cost estimators’ judgements on cost contingencies in highway construction projects. Seven of them, namely cost estimators’ ability to effectively communicate with stakeholders, self-reflection on previous practice, open-mindedness to project uniqueness, previous project experiences, risk attitude, assumption of the controllability of risks, and perceived quality of tender documents were identified as critical ones. They were grouped into two categories, including expertise-related factors and personal factors. The findings contribute to the lack of research on the subjective factors influencing cost estimators’ judgement-making process in highway construction projects in developed countries. The results also provide new practical insights for general contractors to develop more focused strategies and training programs to enhance the reliability of cost estimators’ judgements on cost contingencies, which can effectively reduce the probability of cost overruns.英国公路工程项目中，未预见额外成本是引发成本超支的核心诱因。总承包商通常会在投标报价中预留应急成本以覆盖此类支出，决策主要依托成本估算师的专业判断。然而，不同成本估算师针对同一风险预留的应急成本金额往往存在显著差异。尽管学界已针对影响应急成本估算的客观因素开展了大量研究，但对主观因素的探索仍较为不足。为此，本研究通过质性研究方法探究影响成本估算师判断的主观因素，以填补这一研究空白。研究选取英国建筑业总承包商的资深成本估算师作为调研对象，共计开展12场半结构化访谈；后续还邀请7名英国建筑业资深成本估算师开展焦点小组研讨，以验证访谈结果的有效性。研究结果显示，公路工程项目中影响成本估算师应急成本判断的因素共计13项，其中7项为关键影响因素，分别为：成本估算师与利益相关方的有效沟通能力、过往实践复盘能力、对项目独特性的开放接纳态度、过往项目经验、风险偏好、对风险可控性的预设，以及对投标文件质量的感知。上述关键因素可划分为两类：专业能力相关因素与个人特质因素。本研究成果弥补了发达国家公路工程项目领域中，关于影响成本估算师应急成本判断决策过程的主观因素研究的空白。研究结果同时为总承包商提供了全新的实践参考，助力其制定更具针对性的策略与培训方案，以提升成本估算师应急成本判断的可靠性，进而有效降低成本超支的发生概率。