London has introduced tougher rules for building new high-rises in its financial district that take into account the impact of wind conditions on cyclists and pedestrians.

It is the first time in the UK that the effects of windy microclimates on cycling comfort and safety have been considered, according to the City of London Corporation, the governing body of London’s Square Mile financial district. It also points out that the criteria could form the basis of national and international standards.

London’s skyline has changed dramatically in recent years – the Gherkin, the Walkie-Talkie and the Cheesegrater are examples of famous new additions – and another 13 skyscrapers, including one expected to be 290 metres high, are set to spring up in the Square Mile by 2026.

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Urban microclimates

Tall buildings can generate wind tunnels and downdraughts which occur when wind hits a tower and is pushed downwards.

These gusty microclimates make cycling, walking and sitting down in public spaces unpleasant, and in extreme cases can destabilize pedestrians and cyclists and push them into the paths of vehicles.

The City of London financial district is seen with office skyscrapers commonly known as 'Cheesegrater', 'Gherkin' and 'Walkie Talkie' seen in London, Britain, January 25, 2018. Picture taken January 25, 2018.  REUTERS/Toby Melville - RC1B2AEA7FA0
Recent addition to the London skyline: the Walkie-Talkie.
Image: REUTERS/Toby Melville

Under the new standards, proposed buildings in the Square Mile between 25 and 50 metres tall will have to undergo wind tunnel testing or computer simulations. And those over 50 metres will have to do both with assessments carried out by a separate independent consultant.

Wind speeds of more than 8 metres per second have been reclassified as “uncomfortable” rather than “business walking conditions”, and speeds of over 15 metres per second are deemed hazardous for pedestrians. For areas with restaurants and cafes with outdoor seating, 2.5 metres per second is an acceptable level.

Greater consideration will be given to spaces around schools or elderly people’s homes to prioritize the needs of more vulnerable groups in society, the City Corporation said.

The more robust assessment is part of a plan to make the City a safer and more comfortable place for pedestrians and cyclists, and to promote walking, biking and other outdoor activities. Last year, the average number of journeys by bicycle increased by 6.2% compared to 2017, according to Transport for London.

The volume of cycling journeys increased by 6.2% in 2018.
Image: Transport for London

“With the number of tall buildings in the Square Mile growing, it is important that the knock-on effects of new developments on wind at street-level are properly considered,” said Alastair Moss, Chair of the City Corporation’s Planning and Transportation Committee.

“These guidelines mark another significant step that the City Corporation is taking to put cyclists and pedestrians at the heart of planning in the Square Mile, prioritizing their safety and experience.

“From the Transport Strategy to the City Plan, we are ensuring that our streets are a comfortable and pleasant place to live, work and visit.

“We hope these groundbreaking guidelines can create a blueprint for others by delivering safer, more enjoyable streets that meet the evolving needs of this great City.”