I cycle everywhere - to classes, shopping, work etc
I can easily keep up with traffic (people severely underestimate the time spent at traffic lights) and average 20km/h
It costs way less than a car. 2nd hand road bike ($160) + pump ($10) + lights ($70) + helmet ($25) + chain ($35) = $310
The cheapest car to run (according to NRMA) is $120/week.
...I save so much money that I can afford to get a cab whenever I need to carry stuff.
Having said that, I'm talking about Canberra where every road is quiet/has a bike lane, hills are almost non-existent, and you can take your bike on a fast bus that runs every 5mins all day to access the other suburbs.
In Sydney, I would be quite scared to ride my bike considering the traffic. Plus the hills are gigantic.
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The "sweat" factor isn't really an issue for rides <15mins (which is all I do)
I reckon cycling should be saved in Syd for the western suburbs, as a way for people to access suburban train stations (and maybe regional cities like Penrith, Parramatta and Liverpool) - these places have the room and terrain for good cycling infrastructure to be a worthwhile investment.
Clover's ridiculous bike lanes up King st and Bourke St are way too steep to attract anyone but the crazy enthusiast cyclists.
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Finally, the RTA estimates that cycling 1km has a net benefit of $0.02 (or something close)