All Mr Red's "ifs" can be answered by looking at the countries and cities where cycling has increasingly replaced driving: Amsterdam, Copenhagen, Groeningen, Oslo, etc. Frogs have not rained down on the populace.

Bonzo3legs, registration plates are already installed on cars; I don't see them being used for catching many of the lights-breakers or mobile-phone-users. (In Ireland, phone using in cars is endemic, and very, very dangerous.) A few countries have tried registration plates, but all have abandoned it as a resource-gobbler (vast armies of civil servants to administer it) and useless.

I'm with you on the bells, Mr Red - I have a loud bell on my good bike, and a modern bell on my functional bike. (For some reason, it's now impossible to buy a good loud steel bell of the kind you hear on Queen's I Want to Ride My Bicycle any more; the modern ones seem to be made of aluminium and give a faint, unsatisfying, buzzy ring once attached to handlebars, though they sound satisfyingly loud in the shop. I bought myself an old one, and it's loud, but it's more of a "Ting-Ting" than a "Brring-Brring", which is what I thought I was buying.

Senofou, in relation to knees, ask your doctor. I would have thought that cycling would be much easier on the knees than any other exercises; however, I have a friend (in his forties but weighty) who has been told that he shouldn't cycle because his knees are crocked. But this may be the specific form of knee problem he has, which I think is due to some horrible disease that rots his cartilage. By the way, the three-cornered way your weight is distributed makes it relatively light on bottom, feet and wrists - though a long cycle (100km+) can be wearing on the wrists.

Punkfolkrocker - mooching around online I see some references to recumbent or semi-recumbent (I'd prefer the semi - you sit up, but your legs are straight out rather than down) and arthritis. Again, I'd ask the doc. Semi-recumbents use your back muscles more than your stomach muscles, I vaguely remember.
Here's a video of someone trying one for the first time. (My blood chills at the thought of arthritis stopping one cycling; my thumb has just started to do a nasty getting-stuck thing, solved by giving the joint a jerk to the left with the other hand, and when I crouch I sound like someone scrunching up bubble-wrap.)

Cyclists and drivers and red lights: this RSA (Ireland's Road Safety Authority, not the most cyclist-friendly group!) study of 60 junctions found that just 1 in 8 cyclists went through red lights; it also found that nearly 1 in 10 cars had defective lights, 1 in 7 drivers misused fog lights - and 1 in 4 semi-articulated lorries did. A Kerry study which I can quote if you want found that 67% of lights-breaking was by cars.

Various cities, including Paris, are making some red lights optional for cyclists. I'm absolutely with you on the burly youths who hurtle through lights because "Me! I'm more important! I can go!" - but there are many non-sociopath riders who will go through red lights cautiously if it is safe to do so; the same with one-way streets - a lot of cities allow cyclists to go contraflow down one-ways when it's safe.

For a little entertainment - a TED talk by an Israeli IT student who takes kids from a reformatory out mountain biking.