A speed limit of 20mph has been imposed on all central London roads managed by Transport for London (TfL) in a bid to reduce road deaths.
All TfL roads within the Congestion Charging Zone (CCZ) are subject to the limit since 00:01 GMT on Monday.
Some critics said the speed limit would make no difference because traffic already moves so slowly in the area.
The Vision Zero scheme is a collaboration between the London mayor, TfL and the Metropolitan Police.
Limits have been placed on roads in Millbank, Victoria Embankment and Borough High Street following strong public support for the proposals.
New signage and road markings with raised pedestrian crossings are also being installed in locations where a high number of people walk, including near the Embankment and Tower Hill Tube stations, TfL said.
A study found that about four lives a year were saved when a 20mph scheme was rolled out in Bristol, but similar plans in Manchester were reviewed over concerns they were not reducing the number of accidents.
Some of you may have noticed a new set of 20mph Roundels on High Street, near John Pounds Church – a welcome contribution in all our efforts to reduce speeding in Old Portsmouth.
This is a particularly vulnerable section of High Street owing to the close vicinity of the church, schools, pub, elderly care accommodation and the games centre; and where the community has been calling for a road crossing for a number of years.
The new Roundels are a step in the right direction and much appreciated.
The Community Speedwatch (CSW) team is busy this year on High Street. We record all traffic speeds over a one-hour slot, in a variety of locations and directions. We further note details of those cars whose drivers are travelling at 24mph or over, and who will then receive a caution letter from the police.
The aim of this exercise is to educate drivers of the local 20mph speed restrictions, and put pressure on the local council to enforce those restrictions, making it is safer and calmer for pedestrians, drivers, cyclists and residents.
If you feel like the rest of the CSW team do about traffic issues in Old Portsmouth, please get involved and join us. We are all avid volunteers.