Interesting things you should know...
(the following numbered points are copyright BBC Top Gear magazine - buy the June 2007 issue for more. Italicised sections are my comments)

1) According to Euro NCAP, an Audi Q7 (SUV, villified) is less harmful in a pedestrian impact than a Ford Fiesta (small, 'safe' family runaround).
2) A season of F1 racing burns less fossil fuel than a single transatlantic 747 flight.
3) The Stern Report found that cars make up less than half of all transport emissions in the UK.
4) The average British home emits 1500kg more carbon dioxide per year than a Ford Focus.
5) A car carrier (the ocean-bound variety) burns 1756 tonnes of heavy fuel oil one way from Japan to the UK (that's a lot, and the worst kind, and makes the Prius - made in Japan, shipped worldwide - not suddenly so environmentally friendly. According to an earlier article, that journey adds 1 tonne of carbon dioxide emission to an average 16.5 tonnes for 100,000 miles of Prius driving, a significant amount).
6) Oxford Street is the UK's most polluted street. Most of Oxford Street's length is closed to cars.
7) Like trains, cars are only efficient when they're full. A fully loaded Discovery emits less carbon dioxide per occupant than a fully loaded Smart (of the two-seat variety).
8) Acid rain from mining nickel for Prius batteries has destroyed the landscape of Sudbury, Ontario to such an extent that NASA now uses the area to test drive its latest lunar vehicles.
9) The average saloon car is responsible for its own kerbweight in carbon dioxide per year. The average Brit accounts for 30 times their own body weight.
10) The UK's superminis emit three times as much carbon dioxide as its SUVs.
11) While 85% of cars are recycled by law, trains go unregulated with much of each heading to landfill.
12) A domestic flight emits 400g/km of carbon dioxide, four times that of a small diesel car with only the driver onboard.
13) Despite being smaller and emitting LESS CARBON DIOXIDE THAN A PRIUS, the Volkswagen Polo Bluemotion is not exempt from London's Congestion Charge.
14) Farting cows are responsible for 18% of all greenhouse gases, more than cars, planes and all other forms of transport put together.
15) A Landrover Discovery has a smaller carbon footprint than a London cab.
16) A Boeing 747 emits 400 tonnes of carbon dioxide in 24 hours. It would take 250 cars a year to achieve this.
17) Some electric cars aren't governed by today's safety legislation - I urge you to buy the magazine and see what happens when they crash test a G-Wiz. A technician is apparently heard to utter: "I see these tests every day but I've never felt sick before". Alternatively, the footage is available at www.topgear.com/gwiz.

This isn't going to persuade anyone who's already made their mind up that cars are evil, but banning them from the roads based on emissions is not going to solve the problem. It won't even make us meet the more stringent Kyoto targets. How about targetting homes and businesses instead, environmental lobbyists? Get a clue...