Loads of factors, really.

I'm not interested in cars. Smelly unnecessary wastes of space in my book, particularly in a city such as London, built as it is on an intricate medieval street plan. If I could afford a car - which I can't - I'd get several better bikes.

Cycling is way faster. I used to use public transport for everything. After several years of cycling everywhere within a 18 mile radius around town, I can't believe I ever put up with the slowness, unpredictability and expense of buses and tube trains!

Cheaper - I must have saved almost £5k ($7.5k) over the last few years. The bike cost £500 (reduced from £800 which is what most retailers are charging for the same model right now) and there was the initial outlay for all the accessories including lights, locks, panniers, pannier rack, helmet, gloves etc. totalling around £250. So far this year I've spent nearly £300 on replacement/upgrade bike parts but, for the last three years, I've only spent about £100 a year on parts including tyres, tubes, brake pads and batteries. If I used public transport I'd be spending over £40($60) a week, so £2k ($3k) a year. A brief google search on the cost of running a car in London indicates £2200 or more.

I've been feeling great since cycling every day. Really healthy. I cycle in all weather and don't get colds any more and only get flu once a year, mid February (and mildly at that).

It's fun. SOOO much more engaging than getting on a hot stinking crowded bus or tube carrage. Crazy as London roads are, I enjoy it. It's a manageable kinda dangerous. Keeps life real.