"Reducing the weight of the vehicle per person moved is a key way to improve efficiency and therefore reduce emissions." Zero Carbon Britain 2030
According to the Zero Carbon Britain 2030 policy framework, one way to reduce vehicle weight is for more people to use the same vehicle, whether this be through car-sharing or high occupancy public transport such as buses, trains and coaches.
Another is to reduce the weight of the vehicles themselves.
Over the past 20 years, mid-sized cars have become 20% heavier to accommodate safety features, sound-proofing and accessories (King Review of Low Carbon Cars, Part I, 2008).
Reduced weight would enable the same performance to be achieved with a smaller engine. The King Review found that such "lightweighting" could offer efficiency gains of 10%, at a cost of £250 - 500 per vehicle, while low-rolling resistance tyres and improved aerodynamics could give potential efficiency savings of 2-4% each.
Another approach to weight saving is to make a step-change in vehicle design. Reducing the weight of an individual component produces positive knock-on effects. If one component gets lighter, the car needs less power for the same performance, and so this enables further weight reductions in the power train.