•Passenger body balance is significantly affected by the bus design.•Below 1.0 m/s2, passenger upper body balancing mechanisms are closer to natural.•Above 1.5 m/s2, passengers adopt extreme mechanisms to sustain their balance.•Middle-aged males present worse body balance compared to older.•Stair ascending is the most challenging task aboard for upper body engagement. Whilst buses can improve societal well-being, they can also contribute to increasing car ownership due to their abrupt movements. High acceleration can be responsible for passenger injuries that require hospitalisation and for the development of fear of falling in the elderly, which turn people away from buses. Hence, to promote buses as a form of active transportation, passenger safety needs to be considered in public transport planning. The walking pattern and grip force behaviour of 29 healthy and regular bus users, between 20 and 80 years, was studied with the aim to increase passenger safety aboard buses. Lower body balancing mechanisms were previously published. This work reports on the balancing mechanisms the same participants developed to engage their upper body when subjected to the same acceleration levels (stationary: 0 m/s2; low: 1.0 m/s2; medium: 1.5 m/s2; high: 2.5 m/s2), and whilst performing level and stair walking tasks. Their natural grip force and weight was also considered. ANOVA tests on the collected peak grip forces and grip durations revealed that age, gender, task and acceleration are significant factors in the development of upper body balancing mechanisms. Peak grip force and duration intensify, and become less variable, as acceleration increases, especially during stair ascending. Middle-aged males present higher instability compared to other passengers, as they apply higher grip forces and sustain their grip for longer durations. As the upper and lower body work in synergy to sustain balance, conclusions on an overall acceleration level are being drawn to increase bus passenger safety.