User participation in design or innovation projects is nowadays highly recommended in various domains. The main motivation is that their participation enables developing products that fit well users' needs and then that are more easily accepted by customers. Especially in the context of creative design, i.e. when expected solutions should be both novel and appropriate, studies have observed that several factors can impact the solutions' level of creativity, such as the quality of collaboration between experts and users. This study aims at determining the effect of user participation in creative workshops with designers, focusing on three aspects: the level of creativity of the final solution, the quality of the creative process and the quality of collaboration. The study has been conducted in the context of a real project whose objective was to find new solutions for transportation services in a given geographical area. The ultimate goal is to identify facilitators and barriers in the collaboration between users and experts, in order to provide optimal tools to support the contribution of every stakeholder and then to achieve highly creative solutions. The method was as follows. Eight creative workshops were organized. In five of these workshops, experts in transportation and mobility had to collaborate with employees of the area who were considered as users. In the three other workshops, experts collaborated with each other without any participation of users. All the workshops were audio and video recorded, in order to analyse both the creative and the collaborative processes.