Improving cycling infrastructure enables a sustainable alternative to short car trips and last-mile solution, but change relies on interventions with resistance to policy deprioritizing automobiles. This research evaluates improvement (completed 2015) to the Plain Roundabout in Oxford, UK, a ‘safety hot spot’ and cyclist deterrent, focusing on procedural elements of cycling design. Thirteen semi-structured interviews with expert stakeholders (February-May 2015) and cyclist testimonials were collected. Thematic and discourse analysis investigated transcripts and documents, identifying four main ‘resistance in experimentation’ themes with 11 sub-themes. Materiality identified physical layout, design details, and geographical boundaries as problematic. Institutionalisation identified modelling tools and data availability, built-in skillsets, and experimentation culture as important to successful intervention. Agency/Politics identified stakeholder involvement, time, and resources as further key elements. Discourses identified a norm of unfettered motorised movement, the freedom of choice and self-responsibility, and compromises and balancing as additional important considerations. Results challenge experimentation as a sure way to enable sustainable mobility changes. Infrastructure deprioritising motorised modes requires questioning modernist values of speed and (car) flows. Safety, though touted as important, does not sufficiently justify radical change. These findings provide considerations about potential experimentation pitfalls to policy-makers, ideally improving approaches to cycling infrastructure interventions.