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Smart motorways and there contribute to the sustainability of the UK transport system.

Smart motorways throughout England as defined by Highways England, have the objective to deliver more efficient motorways through the application of smart infrastructure technologies to improve real-time management of major motorways, including actively managing traffic, improving journey times and reliability, increasing capacity, reducing congestion, and maintaining safety levels (Arcadis, 2017). There are three main types of smart motorways, each having a slightly different way of operations (AA, 2020).

Firstly, the controlled motorway has variable speed limits and a hard shoulder for emergency use. Dynamic hard shoulder motorways have a hard shoulder that could be opened up to traffic in congested periods as well it has gantry overhead signs indicating when driving is allowed on the hard shoulder. Furthermore, the all-lane running system has no hard shoulder with emergency refuge areas located approximately every 2.5km or 1.6km (Jallow, 2019).

A Guerrieri comparison of a 1-km long section of conventional and smart motorway found that the highest environmental impact during a motorway life cycle is always due to vehicle emissions and specifically of platooning vehicles (Guerrieri, 2020).

As the main goal of smart motorways is to improve the flow of traffic, this will have a big influence on the increase of the use of cars since capacities increase and the mode becomes more desirable by users with the effect of increasing carbon emissions.

Someone could argue that improving the flow of traffic will reduce the number of times vehicles' engines are running hence reducing the environmental burden simultaneously, as reducing congestions and improving user’s experience.

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Others may argue that improving the capacity and flow of motorways and not promoting investments in other public transports, increases the number of cars, hence increasing emissions and negatively impacting air quality of the surrounding areas.

The decarbonization of transport is mostly a challenge of energy rather than mobility. In the research paper “How to decarbonize the transport sector?” Zwaan stresses that a radical change in the automotive industry should occur with hydrogen becoming the dominant transport fuel for achieving a net-zero transport network (Zwaan, 2013).