This research investigates the speed behaviour and safety effects on cyclists and mopeds sharing the cyclist T-Intersection with and without the application of a lane marking nudge. Unsignalised cyclist T-Intersection gives rise to more safety-critical instances, which include unsafe braking and evasive maneuvers. It is also found that uncontrolled T-intersection can create an issue when priority is assigned to the intersecting (right) arm because drivers on the straight road have a high perception of priority and fail-to-yield. Even though many studies have analysed the positive influence of the lane markings for cars, the influence of it on cyclists have not been explored. The safety criticality in this research is investigated using critical deceleration and jerk as Surrogate Safety Measures, because they are found to perform better at identifying potential conflicts compared to other time proximity measures, such as Time to Collision. Based on the results, the nudge did not show any strong evidence for reducing the speeds or safety criticality at the T-Intersection. So, it cannot be implemented as a traffic calming measure at the T-intersection without further research or modifications. So, this research also suggests key improvements with the lane marking nudge, and some crucial changes have to be implemented to avoid these kinds of unexpected outcomes in future. So, an elaborate discussion is made on what could be the possible changes with the implementation of the nudge for further investigations. Few intervention functions from the MINDSPACE framework and improvements from the behavioural change wheel have to be considered in the future researches with nudges.