Staying on freeway more fuel efficient when 15% longer route?

Supposing your morning commute is about 10 miles by the shortest route available, but you can get to your destination faster by staying on the freeway, which goes about 2 miles out of the way. The extra 2 miles are all travelled on the freeways at optimum freeway speeds. The shortest route alternative requires that you get off the freeway at about the halfway point, and take a major thoroughfare which also moves very well at the time of day involved, but still involves the usual stops along the way.

So is it more fuel efficient to stay on the freeway and go a couple of extra miles, or to take the surface roads and minimize the actual distance?

In your scenario with my car.

Normal 10 mi @ 28 MPG or .357 gal of gas
alternate 7 mi @ 35 mpg .25 gal of gas + 5 mi @ 28 MPG = .178 MPG total of .428 gallons.

Short path is better.

It seems to me as though you got the routes mixed up, drachillix

Freeway route:

Shortest route:

So, they are equal in terms of gas usage. Of course, YMMV.

If you’re saying the freeway is shorter time-wise, it may be close to a tossup, depending on the number of stops on the “shorter distance” route, Keeping in mind that a car gets BETTER gas mileage at a constant 35 than it does at a constant 65… If I were you and the time were close to even, I’d drive the shorter route in terms of miles because it would lead to less miles on my vehicle and therefore a higher resale value down the road, and possibly lower insurance rates now because you’d be driving about 1000 miles less per year (2 miles/trip * 2 trips per day * 5 workdays/week*50 work-weeks/year)

So you’d save 1000 (is that right? I always mess up by powers of 10 when doing simple math like that) miles per year, but put a lot more wear and tear on the rest of the vehicle…starting and stopping, and at least around here city streets aren’t as smooth as the freeway. I’d say it’s a pretty nearly non-existant difference either way, so take whichever is faster, or has better scenery, or just alternate. Of course, if it was just an academic exercise, none of this helps at all…