Advanced Stop Lines are the boxes marked on the road with a bike symbol painted inside, located at many traffic lights.
The cyclist has a stop line several feet ahead of the line used by everyone else in order to give bikes more space so they can be seen more easily and are not right in front of a vehicle's bonnet or wheels. However, very significant numbers of drivers are not currently stopping at the rear line.
The Mayor's Cycling Commissioner, Andrew Gilligan, said: 'It may be that some drivers don't realise they aren't allowed over the Advanced Stop Lines, and when the lights are red, those areas quite often have cars and lorries all over them, completely defeating their purpose.
'Bike boxes are a really important way to keep cyclists and vehicles at a safe distance.
'They have already saved hundreds of drivers, particularly truck drivers who have blind spots in their cabs, from the anguish of unintentionally harming a cyclist, and of course saved hundreds of cyclists from serious accidents.'
Drivers caught crossing the first or second advanced stop lines when the signal is red will be liable for a £60 fixed penalty charge and three points on their licence.
The only exception to this rule is if the traffic signal changes from green to amber and drivers cannot safely stop before the first stop line.
In addition to stepping up enforcement on motorists, rogue cyclists are also being targeted.
Whilst most cyclists ride responsibly - some do not, and this can anger other road users. Cyclists will be targeted for jumping red lights and issued with a £30 fine if caught doing so.
Andrew Gilligan added: 'Whilst usually only endangering the rider themselves, bad cycling does annoy and frighten people, and we are going to tackle it.
'We are increasing the number of officers in our dedicated Met Police Cycle Task Force by more than a quarter. Riding bikes themselves, they will target particular cyclist misbehaviour hotspots.'
The start of the increased enforcement of both drivers and cyclists was supported by a seven-week intensive phase of engagement and education run by the MPS and CoLP.
The engagement programme included speaking with drivers and cyclists at key junctions and handing out flyers with information to help improve compliance around Advanced Stop Lines, explaining both motorist and cyclist obligations and the reasons for the rules.
Siwan Hayward, Acting Director of Community, Safety, Enforcement and Policing, TfL said: 'Cycle safety is an important issue for us at TfL. Our aim is not to penalise road users but to help educate them into complying with the rules which is why we have been engaging and educating all road users at key London locations in a run up to this enforcement launch.
Our message is clear; motorists leave room for cyclists in Advance Stop Line boxes and cyclists do not cross the Advance Stop Line box during a red traffic signal.'
Chief Superintendant Sultan Taylor, MPS Safer Transport Command said: 'With a record number of Londoners taking up cycling, cycle safety and security is more important than ever.
'The Safer Transport Command is working with Transport for London and its policing partners to improve road user behaviour across London by ensuring Advance Stop Line rules are adhered to so that cyclists and drivers enjoy harmonious journeys.'
An improved cycling culture in London will also help strengthen the relationship between motorists, cyclists and pedestrians.
The Cycling Vision for London launched by the Mayor this year includes a £1bn plan for improved infrastructure for cyclists and new, safer routes - including a whole network of direct, back-street 'quietways'. Giving cyclists a more defined space of their own will help reduce conflict between them and other road users, and also help attract more women, older people, and more cautious cyclists.