Posted on: September 15, 2018

Melting Roads – The Effects of Hot Summer Weather

The heatwaves do not bode well for roads. The road tarmac in the UK melts in the heat, as happened in Wales in the summer of 2018.

According to Dr Howard Robinson, chief executive of the Road Surface Treatments Association, roads in the UK that experience high traffic start going soft around 50C. While 50C does not look attainable while the air is measured around 30C, the tarmac that lays in direct sunlight and absorbs the heat can reach much higher temperatures.

To avoid road softening the road industry introduced a new asphalt specification to allow asphalt surfaces to be coated with polymer-modified binders following a massive heatwave in 1995, but so far only 1/20 of the roads in the UK have been covered with the polymer, mostly roads that experience heavy traffic all year round.

Roads consist of a few layers on top of one another and melting mainly affects the surface layer. Roads that experience heavy traffics are made with three layers – a surface layer, a binder layer and a base layer. The sheets are respectively 3, 7 and 10-15cm thick. The roads with less, however, such as country lanes are generally made with only two coats.

The rails do not like the hot weather either – “when Britain enjoys a summer heatwave, rails in direct sunshine can be as much as 20°C hotter than air temperature. Because rails are made from steel, they expand as they get hotter, and can start to curve – known as ‘buckling’”. Because of the tracks curving and expanding, trains have to travel at lower speeds to reduce the chances of an accident. In dire conditions, Network Rail makes use of its “extreme weather action team”, a special task force to repel the advances of lousy weather. For heatwaves, one of their tasks is painting the rails white to reflect the heat back into the atmosphere.

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