Why should I ride a bike regularly and leave the car at home?

There are all sorts of reasons:

• Financial Reasons: Bike riding is cheaper. An expensive bike costs five thousand Euros. You can purchase a new reasonable bike for between five hundred and a thousand Euros. A decent two or three year old second hand car will cost you a lot more. 
• Cycling is as quick: Bike riding is as quick as a car over shorter distances, if not quicker, if you take the time to find a parking space for your four wheeled vehicle in to consideration.
• Health Reasons: Bike riding is healthier. 
• Environmental Reasons: Bike riding is better for air quality because you are cleaning the air rather than filling it full of carbon dioxide, carbon monoxide, nitric and nitrous oxides, lung clogging unburnt tar particles, etc. etc. However you should then try to get out of town now and again to give your respiratory passages a chance to recover.
• Patriotic Economic Reasons: Motor cars and bikes need oil to power them. Although Britain does still have North Sea oil, it has imported more oil than it has exported since 2003, so if the country can reduce its appetite for oil, it will spend less money abroad and so improve the balance of payments. Cyclists don't use much oil, so every kilometre you can ride on a bike or walk instead of sitting in a car is good for the nation.