Can sharing car trips deliver meaningful emissions savings? The case of Great Britain

Car and taxi use accounts for 13 % of total UK emissions, with 404 billion vehicle-km travelled in 2023. Yet, much of this car use is inefficient with 64 % of journeys made by a lone driver. Trip sharing is suggested as a method that could reduce this inefficiency. However, no studies have yet assessed prospective greenhouse gas emissions and energy use reductions across all trips and at a national level, without making assumptions about the feasible extent of trip sharing. Here we do this by clustering high resolution data on transport demand to identify trips with similar routes and timings which could potentially be made by trip sharing. A sensitivity analysis of this model is conducted to explore the effect of changing factors such as acceptable changes to trip timings, detours to pick up and drop off passengers and the willingness of the population to participate on the overall vehicle distance travelled, emissions and energy use. We find that trip sharing could reduce emissions from cars and taxis by a maximum of 11 %, with no reduction in overall mobility, which is achieved when the whole population is willing to participate, accept a change to their travel schedules of up to an hour and accept detours of up to 6 km around their intended origin and destination. Practical levels of trip sharing would result in smaller potential emissions savings, which is an important consideration for policy-makers in prioritising interventions to decarbonise transport. • Car use in Great Britain is modelled at a resolution of individual trips. • Multidimensional clustering is used to identify opportunities for trip sharing. • Conditions where trip sharing is beneficial and detrimental are identified. • The importance of factors that determine the impact of trip sharing is quantified. • The ideal vehicle types for trip sharing are investigated.