Hoping, I don't agree with you.... e.g. let me put the calculations another way......
We know that a B737 will ( on average ), when full with 148 passengers, use 736 imperial gallons of Kerosene to fly 500 miles - which it takes about one hour to do.
If we take the same 148 passengers out of the aeroplane and put them into cars - of which you will need 37 ( given four people per car ) - you could donate the same 736 IPG of fuel amongst all the cars - so providing each vehicle with 19.8 gallons with which to cover the same 500 miles.
Now with each car hauling four people and their luggage you will then need their vehicle to see a fuel economy of 25.3 mpg ( or higher ) in order to better what a single B737 is doing with the same 148 people, over the same 500 miles ( at 500 mph ).
Nb. I drive my 1.8 litre petrol powered Ford up and down the the road to LGW nearly everyday - a 68 mile round trip - and on average I get 25 mpg - though I'll admit that I'm nudging the 'disqualification zone' w.r.t to my speed most of the time - but I am the only one in the car.