A large number of the project organisations of large infrastructure construction projects have difficulties coping with the current static and dynamic project complexities. Researches, however, suggest that adding extra complexities to the project could create synergies and therefore new solutions. An increase in project complexity could increase the level of support and appreciation by the project participants and external stakeholders and thereby improve the level of project success. An explanatory case study, with four cases, was used to determine if and how project organisations adapted their project management approach, after the inclusion of a new objective and thereby increasing the number of involved interest groups. In comparison with the results from an individual and cross-case analysis, the needed adaptations for a successful response to the increase in number of involved interest groups could be determined. The changes to the project management approaches as a consequence of this extra objective, were in three of the four projects small to none. Only in one of the projects, considerable changes in the approach were determined. An expert session illustrated that most project management professionals are willing to change their project management approach, when the project is substantially changed, due to for example, a significant change in the project complexity. Nevertheless, the results of the session and the case study do also illustrate that this measure does not happen very often. As a consequence, no conclusion could be drawn on the needed adaptations, because the project organisations showed limited flexibility by only including an extra objective in which the effect on the project were neglectable. This conclusion does however illustrate that project organisations could include and extra objective to their project and thereby increase the number of involved interest groups, without any needed adaptation to the project management approach, provided that the following five conditions are met: [1] the extra objective is small of scale, [2] the project organisation acts a facilitator for the execution of the extra objective, [3] the objective is included to the project in the design phase, [4] complexity dimension “social complexity” is present on the project and [5] the extra objective is properly analyses and a supporter for the objective is appointed. The developed theoretical framework from this research could be used to further analyse the composition of project management approaches in the current infrastructure construction projects. This would contribute to a better understanding of how project organisations compose a project management approach when specific complexities are expected.