A 20 mph speed limit has been introduced at the roundabout at the southern end of Waterloo Bridge.
The speed limit has initially been introduced on a trial basis and Transport for London says that it will monitor the effect of the change before deciding whether to make the measure permanent.
London's deputy mayor for transport Isabel Dedring told the SE1 website that the speed limit is expected to be largely "self-enforcing" but that action would be taken to back it up if necessary.
TfL chose Waterloo as the venue for Thursday morning's launch of Safe Streets for London, a new road safety plan for London which covers the years to 2020.
"I want London to be the most liveable capital city in the world and improving the safety of our roads is key to achieving this," said Mayor of London Boris Johnson.
"We've made good progress in recent years, but we must do more. London's population is rapidly increasing and the extra demand that this will place on our road network poses a significant challenge.
"That is why I have set a new target to cut the number of those killed or seriously injured by 10,000 – or 40 per cent – by 2020."
TfL says that it received 86 responses to its public consultation on the proposed 20 mph speed limit at Waterloo, with only three people objecting to the plan.
Earlier this year Boris Johnson confirmed that TfL is considering a 20 mph speed limit at Elephant & Castle.