There are a few contributing factors. Its not as simple as slinging a leg over a bike (although its pretty damn close).

1. Cycling does not produce the same stress response as driving. (Although I don’t think they took the stress of sharing the road with two tonne vehicles into acount).

2. Cost effectiveness.

3. Benefits of the physical exercise… etc.

Follow the link and enjoy the rest of the article.

The Science Behind Why Cycling Makes Us Happier