Cycling remains a popular mode of transportation, yet cyclists are vulnerable road users that face numerous safety challenges. Although human factors research typically focuses on motor vehicle drivers, studies addressing active transportation users, like cyclists, are scarce. The unique aspects of cycling, such as physical effort, exposure to the environment, and disconnected infrastructure, can affect cyclists’ mental perception, workload, and behavior, which are argued to influence their safety on the road. Therefore, this scoping literature review identified factors influencing cyclists’ workload and explored different measures used to quantify mental workload. The findings highlighted age, infrastructure, portable devices, and type of bike as factors that could affect workload levels. However, research on cyclists’ workload from their perspective is limited. This paper summarizes three types of workload measure: subjective, performance, and physiological. These have been used to quantify workload in relation to cyclists and in other settings. We reflect on their benefits and challenges were they to be used to quantify cyclists’ workload. Our discussion emphasizes the need for future research to take a comprehensive approach that considers multiple factors simultaneously to gain a more holistic understanding of their collective impact on cyclists’ mental workload. Moreover, we emphasize the importance of supplementing subjective workload measures with psychophysiological ones for better accuracy and reliability. The review revealed a lack of data and guidelines specific to cycling infrastructure, contributing to cyclists’ vulnerability, and underscored the need for previous findings to be translated into actionable recommendations to improve cyclist safety.