Highways England (HE) is proposing to reduce the motorway speed limit for all traffic, including “zero” tailpipe- (but in practice merely geographically displaced) emissions electric vehicles, to 60mph on some stretches. This is ostensibly to curb emissions. This measure will not deliver any meaningful NOx, PM2.5 or PM10 emissions reductions.
In 2017, car and taxi traffic (c.30.5m vehicles; covering 409.4 BnVkm) represented nearly 78% of UK’s annual road mileage travelled, but only generated respectively 13.5% of national NOx and around 5% each of national PM2.5 & PM10s (see figure below, and: https://www.abd.org.uk/political-establishments-persecution-of-car-drivers-is-totally-unjustified/).
Most public transport, heavy and light goods vehicles are already electronically limited to less than 60mph by law, so their motorway emissions will be unaffected by any limit reduction.
What HE apparently totally fails to grasp, demonstrating a disappointing lack of comprehension of emissions science; (and consequently an organisational fitness-for-purpose deficit) is that problem vehicle emissions peak at low speeds, not at elevated ones (see figure below, and: http://content.tfl.gov.uk/london-exhaust-emissions-study-developing-a-test-programme.pdf, pp.18-35).
Substantially the highest emissions occur at speeds consistently below – and under acceleration to – 30mph.
Additionally, while motorways only represent 0.9% of the UK road network, they carry 21% of its road traffic.
Each 1 mph reduction in average traffic speed costs the UK economy in excess of £1Bn in lost productivity through extended journey times. A 10mph speed reduction for 78% (car/ taxi) of motorway traffic is equivalent to £1Bn x 0.78 (% cars/taxis) x 10(mph reduction) x 0.21% (% of annual mileage) = over £1.5Bn in annual lost productivity for no environmental gain. This at the very least amounts to economic mismanagement bordering on irresponsibility, just as the UK economy seeks to claw its way out of a deep, Covid-19 generated downturn.
HE should be facilitating enhanced traffic flow, and supporting the introduction of a motorway speed limit at least 80mph, in line with 85th Percentile Principles. Instead, it is proposing virtue-signalling, economically damaging reductions which will yield no tangible emissions benefits.