Maybe it's a lack of roadworks, maybe it's the ski season, or maybe it's the Congestion Charge Western Extension Zone (WEZ) abolition, but whatever the cause, the roads in Central London definitely seem quieter in January than they did last year.
The WEZ theory is that people were driving their 'tractors' from Chelsea into the West End at a nominal charge, whereas now they have to pay the full congestion charge. That makes some sense, and it was a weakness of the WEZ. However, private cars made up fairly small proportion of Central London traffic last year - most of it is black cabs, private hire vehicles and commercials - so I'm not convinced of the explanation. Not that I have a better one, mind you.