Background Bikesharing is a versatile intervention, that enables cheap and convenient cycling for urban populations, and according to recent literature, has a positive impact on health, safety and the economy. Many of these impacts are based on the assumption of a modal shift induced by bikesharing, i.e. implementing a Bicycle Sharing System (BSS) will increase population cycling. However, the evidence is inconclusive. The aim of this study was to evaluate if the intervention of implementing a BSS increases cycling. The study was conducted using bicycle count data from Helsinki between 2014 to 2018. Methods A controlled interrupted time series design was used in combination with segmented regression as the method. An intervention series and a control series were analysed separately. The slopes (trend) and intercepts (level) of pre-intervention (2014&2015) segments were compared with post-intervention segments (2016-2018). The same analysis was performed in both intervention series and control series.  ResultsThe results from the intervention series showed an increase of 105% in the level of the outcome after the implementation of the intervention. Simultaneously, the control series showed that the underlying trend of cycling remained largely unchanged during the whole study period (level increased by 3%). Stratified analysis supported these results in both intervention and control series.   Conclusion The analysis of the intervention series revealed, that the level of the outcome increased sharply after the intervention, implying that the intervention had an immediate effect. However, the lack of statistical significance in the analysis of the slopes made it impossible to determine if the effect was sustained.