Petrol vs Food vs Miles...

I have been driving to work recently and noticed that I have been spending approx £20per week on petrol.  So I decided to do some maths to work it out if I can subsidise my food intake and or cycling fund...

The human body consumes approx 700-1000kCal per hour.
It replenishes glucogen stores at approx 500kCal/ hour.
So cycling to work for an hour each way I will burn approx 1400- 2000kCal per day, but replenish my energy levels with a good meal.  And by not driving I get fit and can use that "petrol" money on food or that "special" bicycle fund.

Current Petrol Price = £1.29GBP/Litre
My average petrol  =    40mpg
Converted to Km/L=    14 km/L
Distance traveled by Bicycle per hour = 20km 
Fuel saving for the return distance (2 hours riding) =  £3.60    
5 return commutes per week… £    18.22 - lets face it you cannot go far on £1.88 worth of petrol, so my £20- per week works out....  

Remember this is £20- extra that I "could" spend on food on top of what I normally spend on lunch.  That is £80-100 per month and £1000 - 1200 per year.

Here are some more fuel efficient vehicles as a comparison.   I have heard the following "eco-car" referred to as the "smug" car, as the owners think they are saving the planet etc.  I feel smug riding a bicycle..  

Average Toyota Prius — Hybrid H4 Hatchback Mileage = 48mpg
Converted to Km/L= 17 km/L
Fuel saving for the return distance (2 hours riding) =  £3.00    
And even the most economical cars...
Very efficient Car with wind assist  = 60mpg
Converted to Km/L= 21km/L
Fuel saving for the return distance (2 hours riding) =  £2.40    

Conclusion; Maths does not lie the bicycle will pay for itself.