Claim: cutting speed limits could slow climate change


The assertion being of course that human-caused emissions of the trace gas carbon dioxide somehow have a specific effect on the Earth’s climate, which must be countered. But if everyone is forced into electric cars, the speed limit argument becomes obsolete. Lower speed limits also mean more vehicles on the road at any one time, trying to complete their journeys, which in turn could lead to more traffic delays, potentially undermining the whole idea. As usual they conflate pollution and climate arguments to cause confusion.
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Canadian cities from Edmonton to Montreal are lowering speed limits, primarily in an attempt to save lives, says CBC News.

But slowing down may also be an easy way to reduce greenhouse gas emissions and air pollution — not just on urban roadways but also on highways (and even the high seas).

According to Natural Resources Canada, driving a vehicle with an internal combustion engine at 120 km/h burns 20 per cent more fuel than driving at 100 km/h.

An Ontario law that requires trucks to install technology to limit their speed to 105 km/h was estimated to have reduced greenhouse gas emissions by 4.6 megatonnes between 2009 and 2020.

That’s largely because air resistance increases exponentially at higher speeds, reducing a vehicle’s fuel efficiency and generating more pollution per kilometre.

In addition, certain pollutants such as nitrogen oxides are generated mainly at higher speeds, said Marianne Hatzopoulou, professor and Canada research chair in transportation and air quality at the University of Toronto.

That’s the reason the Netherlands recently cut its daytime highway speed limits from 130 km/h to 100 km/h. But Hatzopoulou said cutting speed limits can reduce emissions on city streets, too.

In both cases, it’s not just your maximum speed that counts but how often and how much you speed up and slow down, as a result of things like congestion and traffic control. “All these acceleration events will actually lead to higher emissions,” she said.

If a speed limit is set at 70 km/h, for example, cars try to accelerate to that speed at a green light, cruise very briefly at 70 km/h, then rapidly decelerate at the next red light. If the speed limit is 40 km/h, there’s a lot less acceleration and deceleration, Hatzopolou said.

Lower speed limits have indirect climate benefits, too. They can discourage car travel and, by making streets safer, encourage walking and cycling.

Full article here.

via Tallbloke’s Talkshop

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August 14, 2020 at 03:51AM

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