Londoners are being encouraged to make short journeys on foot to help cut pollution and improve fitness.
Walking 2k takes about 20 minutes
Transport for London (TfL) is urging people to walk either part or all of a journey in the city and clock-up at least two kilometres every day.
Research for TfL showed that half of all car journeys in outer London are less than two kilometres.
The campaign culminates in London's Walking Weekend on 15/16 September with free guided walks in every borough.
According to TfL about 30m journeys are made every day in London and this is expected to increase by four million journeys a day by 2025.
It claimed if every Londoner walked 2k a day instead of taking public or private transport, collectively, 27.3bn calories would be burnt off - the equivalent of more than 100m chocolate bars.
Walking two kilometres takes around 20 minutes, at an average pace, and burns off about 75 calories.
Adrian Bell, from TfL, said: "Not only is a 20 minute walk better for you but it'll be better for London too.
"Walking can play a key role in reducing traffic congestion as well as bringing environmental benefits, which is so important for all our futures."