Science·What on Earth?

How cutting speed limits could slow climate change

In this week's issue of our environment newsletter, we look at how speed limits affect emissions and examine how many countries have net-zero targets.

Also: Which countries have net-zero emissions targets?

(Sködt McNalty/CBC)

Hello, Earthlings! This is our weekly newsletter on all things environmental, where we highlight trends and solutions that are moving us to a more sustainable world. (Sign up here to get it in your inbox every Thursday.)

This week:

  • How cutting speed limits could slow climate change
  • Which countries have announced net-zero emissions targets?
  • Vancouver is creating heat maps to combat warming

How cutting speed limits could slow climate change

(Francis Ferland/CBC)

Canadian cities from Edmonton to Montreal are lowering speed limits, primarily in an attempt to save lives. 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 the same distance 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. 

The city of Prince George, B.C., advocates reducing downtown speed limits to 30 km/h specifically to encourage walking and cycling as part of its 2020 climate mitigation plan.

"Slower speeds … actually create liveability," said Sandy James, a Vancouver-based urban planner who has been advocating for lower speed limits for years. 

James thinks it's a message governments are starting to get. She noted that Europe is beginning to mandate the use of intelligent speed assistance in new vehicles. The technology limits a vehicle's speed based on local speed limits. 

Meanwhile, the U.S. National Association of City Transportation Officials recently recommended setting lower urban speed limits based on safety, as well as local urban density and activity, rather than the traditional method of gauging how fast drivers are comfortable driving.

Regardless of the posted speed limit, individual drivers can actually reduce their fuel consumption (and emissions) by 15 to 20 per cent through improved driving habits alone, according to Ralph Sims at Massey University in New Zealand.

Here are some eco-friendly driving tips from Hatzopoulo:

  • Stick to the posted speed limit (or go slower if there's congestion or traffic signals ahead).
  • Keep a steady pace (cruise control can help).
  • Accelerate and decelerate slowly.
  • Limit the number of times you change speed — this may mean fewer lane changes and less passing.

Emily Chung

Reader feedback

Last week, Emily Chung wrote about how beekeeping in urban settings could be harming native bee species.

In response, Tom Kruesel said: "As an urban beekeeper, I can see some validity in the concern over competition between honeybees and native bees and wasps. (Many of which are also pollinators.) However, my personal experience has been the exact opposite. When I started keeping bees, I also started planting massive amounts of flowers in my yard and on the city boulevard. As a result, I have counted 15 different pollinators that, in my previous 10 years at the same address, I had never seen. And I rarely see any honeybees on the flowers in my yard that are visited by the bumblebees. Bumblebees (easiest to see) seem to wax and wane from year to year, but this year — my fourth with honeybees — the bumblebee population seems to have exploded."

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Hot and bothered: Provocative ideas from around the web

  • A couple of weeks ago, a Japanese tanker leaked about 1,000 tonnes of oil off the coast of Mauritius, an island of about one million people in the Indian Ocean. The country is madly trying to contain and clean up the slick — and that includes using human hair. As one eco-activist pointed out, "Hair absorbs oil but not water."

  • Over the years, the tech industry has promised many "solutions" to a variety of challenges in modern life. One recent example is wireless charging for your devices. No more annoying cables — what could be sweeter? Well, it appears that from an environmental angle, wireless charging could have a serious downside: one writer calculates it requires 47 per cent more power to get the job done.

Vancouver is creating heat maps to combat climate change

(Ben Nelms/CBC)

A horde of cyclists and electric vehicle drivers will soon take to the streets of Vancouver to map out the hottest and coolest parts of the city — a move that will help inform future plans to mitigate rising temperatures.

It's called heat mapping, which is an urban planning tool other cities across the world have used to identify which neighbourhoods are most susceptible to increased temperatures amid global climate change.

"It's a really neat citizen-science project," said Stephen Sheppard, the director of the University of British Columbia's Collaborative for Advanced Landscape Planning. "Obviously, things are going to get a lot hotter in the summers [ahead]."

The collaborative is partnering with the city to carry out the project. About 60 volunteers are expected to participate in the city's heat map project. Each will traverse a route in the city, equipped with high-tech sensors to monitor temperature as they travel.

The city recruited cyclists and EV drivers to do the mapping, so as not to emit any greenhouse gases while collecting data. Volunteers will travel the route three separate times throughout the day to collect a range in temperatures.

"One reason to do it is to have a much more accurate, precise map of not just neighbourhoods but local areas, green spaces, places that could be cool refuges in really hot areas, and also places that are very vulnerable to heat and health effects from heat waves," Sheppard said.

Organizers are targeting a hot day in late August to run the program.

According to Sheppard, the project will establish baseline temperatures for neighbourhoods across the city. Plans are to continue mapping in the years ahead, tracking overall changes in heat.

"Most people aren't that familiar with the predicted effects of climate change and how much hotter it's going to get," said Sheppard. "The popular meme is that we're going to be as hot as San Diego in the summer by mid-century, and that means a lot to people's health and well-being."

In a statement, the city spokesperson said the data will provide information to help guide the city's urban planning, public health and urban greening initiative.  Sheppard said that means adding things like water features, cooling stations and green space in hotter neighbourhoods.

It will also identify areas where the city can enhance the tree canopy.

"This can reduce temperatures by several degrees, and that's what we're going to need in these commercial areas and residential areas with very low tree canopy, like in East and South Vancouver, where it's going to get very hot," said Sheppard.

Vancouver has some of the lowest canopy coverage of major cities in Canada — it's currently at around 18 per cent. The city's goal is to bring that number up to 22 per cent.

Sheppard said it's never too early for residents to contribute.

"We need a lot more people aware of the problem and planting trees now in their gardens, not only so they can cool themselves but their neighbourhoods in 10, 12, 25 years, when it's going to be a lot hotter."

Jon Hernandez

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Editor: Andre Mayer | Logo design: Sködt McNalty

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