The speed limit was introduced across 28km of roads in Camden, Islington, Hackney, Haringey and Tower Hamlets today (March 31).
The limits will be introduced on sections of the A503, A501, A41, A1, A10, A11 and A1203.
They will be supported by new signs and road markings and Transport for London (TfL) said it is working with the Met Police to ensure drivers understand the changes.
Banners attached to street lamps in the new 20mph areas will also be put in place to increase driver awareness of the new speed limit.
Following implementation, TfL plans to carry out monitoring to determine whether further measures to reduce vehicle speeds are required.
According to TfL, indicative monitoring of the 20mph speed limits introduced on roads within the central London congestion charging zone shows a significant reduction in the number of collisions since its introduction.
Data collected from May 1, 2020 to June 30, 2022 shows the number of collisions has reduced by 25 per cent (from 406 to 304), said TfL.
Collisions resulting in death or serious injury have reduced by 25 pc (from 94 to 71).
London’s walking and cycling commissioner Will Norman said: “TfL data shows that 20mph speed limits are reducing the number of collisions on London’s roads, highlighting how important the continued expansion of the 20mph programme is.
“Lowering speeds is one of the most important things we can do to reduce road danger and we’ll continue to work with TfL, the Met Police and London’s boroughs to make it easier and safer for people to walk, cycle and use public transport, creating a safer, greener London for everyone.”
Penny Rees, TfL’s head of healthy streets investment, said: “We’re committed to eliminating unsafe speeds across our network and will work closely with the police to ensure the new speed limits are robustly enforced.”
Mayor of Hackney Philip Glanville said the borough is delighted the new speed limit is being introduced in Seven Sisters Road, Stoke Newington High Street, Rectory Road and Stamford Hill, joining nearly all other main and council residential roads in the borough.
“This is an important moment for so many of us given the impact of speeding in these locations,” he added.