My car gets 7km/100. So around $15 in petrol plus another $1 in costs (being generous). Compared to $5 fuel + $5 tolls on the shorter route plus 40 minutes saved. Assuming there are tolls at all.
And another thing..
Ever been in MCY during the existing peak periods? There is about 20% of the required seating and 50% of the space needed to be civilised. Adding another few 737 loads to that mix will complete its descent into hell. Luckily though, those 737s will be mostly empty.