Following urbanization and higher sustainability goals, large and complex

infrastructure construction projects are becoming more common. New collaborative

contracting models are increasingly used to tackle this complexity and uncertainty. In

a public context, collaborative contracting may be seen as an international trend in

public policy, which is implemented in projects by public clients world-wide. Since a

few years, the Swedish Transport Administration recommends that a two-stage Early

Contractor Involvement should be used for very large and complex projects. This

paper analyses the implementation of this model in two sub-projects in a large

Swedish infrastructure project based on policy implementation literature. Altogether

24 interviews were performed in two rounds, capturing both early expectations and

experiences gained after the contracts had been signed. Participants expressed

positive attitudes to the new collaborative project practices. However, the

implementation process was characterized by ambiguity and many issues about

staffing, collaboration processes, target cost estimations, responsibilities and design

output were left to the projects to resolve. The study shows how conflicting policies

and high project-level autonomy combine to counteract organizational learning and

homogenization of practices in this field.