The Government is keen to see the electrification of heat and travel and the Sixth Carbon Budget (Committee on Climate Change) and Energy White Paper appear to rely on the same for industry if carbon reduction budgets are to be met. However, there is complete silence over the role being played by the national speed limit (ie 70mph on dual carriageways usually enforced at 80mph or higher).
GreenSpeed has been campaigning for a 55mph limit for over 25 years due to the multiple and non-trivial benefits: lower carbon, lower noise, power-shift to smaller and more efficient vehicles, modal shift to low carbon buses/trains, cycling and walking, fewer and less serious accidents and associated trauma. The more efficient driving was resisted by the Treasury due to the reduced tax revenue. The Government was also concerned about the relationship between driver and police! The Treasury now accepts that the emergence of the EV will reduce the tax from fossil fuel use and is looking for an alternative(s).
Since the Environmental Audit Select Committee recommended a lower speed limit to 'reduce carbon emissions from transport' and to indicate to the public that the Government was 'serious about climate change' and 'not running away from tabloid headlines', there is now an even more compelling need for a 50mph speed limit, the move towards electric cars.
An EV has an optimum speed for maximising its range of between 30mph and 50mph. The range (of between 100miles and 300miles) can be increased with bigger batteries, adding weight and materials to the new car and its batteries. In fact the carbon embodied in a new car creates a carbon 'debt' only recovered by driving many miles (hence the need for car sharing/clubbing). Internal combustion engines are also most efficient at around 50mph but have far greater range and fast refueling. A 50mph limit would reduce if not remove the competitive advantage of an ICE being driven at 70mph + over an EV being driven to maximise its range. The differential speed that is responsible for a significant number of traffic accidents would be eliminated (many HGVs already adopt 50mph or less to save diesel). The speed of coaches using the overtaking lanes could be increased from 60pmh to attract car drivers. The lower speeds tend to reduce congestion that currently wastes time and fossil fuel (when not a motor that cuts out when stationary). Vehicles designed for a maximum speed of about 50mph are less polluting at lower speeds (ie 20mph). This lower limit can increase pollution from current ICEs designed for 70mph and above.
These are separate and related reasons that justify the lowering of the national speed limit. What is emerging from the carbon budgeting is the demand that will be placed on electricity generation and supply implied by EVs, heat pumps and the electrification of the manufacture of new cars and batteries (as well as new buildings the Government says are needed ie through MMC).
The lower speed limit would make EVs relatively attractive, increase their numbers and, therefore, the demand for en-route re-charging. If the EV fleet was legally limited to 50mph it would reduce the demand for charging points and the time taken for re-charging in the order of 30% (I don't think that this has been modeled). In the context of the surge in demand for electricity for heat and industry this is very significant. Meanwhile carbon emissions from the tail of the ICE fleet would also be reduced by about 30%.
And correspondence with the DfT that is writing its Decarbonisation of Transport strategy suggests that there is nobody looking at the systemic impact that the national speed limit is having!? The DfT official that said in 2006 that a lower speed limit was 'necessary but politically impossible' could not have been more right then, and is being proved to be even more right now, when the case has become even more pressing.