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How heat affects roads, trains and planes

By Emily Clark, Sunday January 7, 2018 - 11:57 EDT
ABC image
Parts of the Hume Freeway have melted near Broadford in Victoria. - ABC

Roads can soften, train tracks do expand and, when temperatures are high enough, the book on how to fly some planes literally hasn't been written.

This is how heat can affect the three modes of transport we depend on most.

Roads

They could "melt" or soften and become sticky.

Road are made up of a gravel base, bitumen and then aggregate (crushed rock).

Professor Frank Bullen specialises in road pavement engineering and says: "The role of the bitumen is to hold the aggregate in place for the traffic to go over."

"Now, for various reasons the aggregate may be embedded into the bitumen or there's too much bitumen put down, or the traffic levels increased to a great amount and the road surface can become flushed," he said.

"This is OK, unless it becomes very hot."

Parts of the recently.

Professor Bullen explained it with the help of this photo:



"You can see the difference in the colour of the road. You see the black wheel paths, that's where the road has become flushed," he said.



Bitumen is "viscoelastic" so it responds to heat. As the temperature increases, the bitumen becomes sticky.

"If you've got high temperatures and low viscosity, and a flushed surface, the traffic may then pick up the road surface. In other words, The bitumen sticks to the tyres," he said.

A spokeswoman for VicRoads said hot weather could result in "bleeding of the road surface, which occurs when the bitumen becomes reactivated by warm temperatures and becomes soft and sticky".

"This, combined with higher than usual traffic volumes, has affected the pavement on the southbound carriageway of the Hume Freeway between Tallarook and Broadford," VicRoads said.

The temperature in the area hit just over 30 degrees Celsius at 5:00pm on Friday afternoon.

Flushed roads are an issue in the heat but also in the wet.

A technical note issued by VicRoads on pavement safety provides advice on how to "avoid flushed bitumen in sprayed seal surfaces".

It reads:

"Flushed, bleeding and smooth sprayed seal surfaces can result in reduced skid resistance."

"The worst thing about flushed surfaces is they have no texture, which means they don't have skid resistance when vehicles brake," Professor Bullen said.



Rail

Trains are likely to go slower.

It's common practice for rail operators to slow trains down during periods of high temperatures because tracks can "expand" or "distort".

In Melbourne, on how the heat affects its system.



"When the track temperature of a line reaches 55 degrees or higher, the maximum speed limit is restricted to 80 kilometres per hour," it reads.

"The tracks can expand in extreme temperatures and trains must travel at slower speeds to ensure customer safety."

When the ambient temperature is forecast to reach 42C, the maximum speed is reduced to 70kph, according to Metro Trains. Its trains usually run at 110kph.

this weekend.

Adelaide Metro has a plan that defines "extreme heat" as "two or more consecutive days with forecast 40C plus temperatures based on the Bureau of Meteorology website".

That plan to reduce services mostly affects weekdays, but "trains may also operate at reduced speeds as a safety precaution," according to .

will also limit speeds during extreme temperatures, as will .

"Heat speed restrictions have been imposed every summer in Perth for more than 30 years," information published by TransPerth reads.

"However, the impact has been greatly reduced as the Public Transport Authority has progressively replaced wooden sleepers with concrete.

"Track with concrete sleepers is much less affected by the heat."



Air

Planes can be delayed or grounded.

In June, several major US airlines as temperatures soared to the high 40s.

American Airlines cancelled flights out of Phoenix after temperatures reached 49C.

Aviation experts said hotter air was also thinner, causing a decline in performance for jet engines, especially during take-offs.

Also, there might not be any instructions on how to fly the aircraft when the temperatures get too high.

looked at the how extreme heat affects planes.

"The July heat-related Phoenix flight cancellations happened at least in part because airlines' operational manuals didn't include information for temperatures above 118 degrees Fahrenheit (47.8C) — because that kind of heat is historically uncommon," authors Ethan Coffel and Radley Horton reported.

"It's another example of how procedures may need to be updated to adapt to a warmer climate."


- ABC

© ABC 2018

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