Need Help with Route Choice

[jivany]

I need some help with choosing the best route for my daily commute. I basically have three options:

1. 46km (92km round trip, backroads (80km/h limit), gravel for 12km lots of stop signs and traffic lights, virtually no traffic and open fields for almost half of the trip.
2. 50km (100km round trip) backroads (80km/h limit), no gravel a few less stop signs, slightly more traffic than previous option (since avoiding the gravel roads).
3. 55km (110km round trip) multi-lane highway (100km/h limit), reasonable traffic, lots of opportunity to follow transports.

All the routes are basically flat with a few minor hills.
The best I've recorded is about 7.2L/100km on the highway but I know I can do better with some more changes to my driving habits. I just did the shortest route this past week and managed 7.6L/100km. I'm debating about the middle route as I still have a huge number of traffic lights.

If I take my raw numbers for this week and compare to my "best" on the highway, I see the following:

46km*2*7.6L/100km*$1.265/L = $8.84/day
55km*2*7.2L/100km*$1.265/L = $10.02/day

Therefore I "saved" myself almost $6 this week by driving a shorter distance even though I got worse mileage.

So my dilemma is, what route has the most promise of better mileage? I don't have a Scanguage (well, yet) and I'm calculating everything based on a tank/week of driving. I'd like to start learning some driving techniques but I basically have two very different routes. The backroads have lots of opportunity for me to coast. Unfortunately the majority of it is on the gravel portion as traffic is heavier on the paved portion.

Thanks!

[wagonman76]

Id keep doing what youre doing. And give the middle one a try. Go with the one that ends up giving you the lowest cost (a little better mpg is not worth it if youve gotta drive a larger percentage in distance to do it, it just means more money spent and more fumes for the environment). Only thing Id consider is if the gravel route (or any one for that matter) is really beat up, take into account any extra repairs you will be doing to your car.

[SVOboy]

If you get an SGII you'll know for sure,

[MechEngVT]

Keep in mind that typically for best economy you will want to fill your tires to high pressures to minimize rolling resistance. This works on hard surfaces (asphalt, concrete). You'll sink in gravel with high tire pressure (think about riding a bike in the stuff). Throwing gravel roads in adds a variable you will have to test and will probably require a real-time instrument such as a SG2 to tell the difference. Because only a portion of your drive is on gravel lowering your tire pressure to have better flotation may lower your overall economy, but it depends on how badly your vehicle sinks in the gravel. Try running the gravel route at the tire pressure you would run on the highway one week and compare to your improved surface routes, but then run the gravel route again another week with lower tire pressure (not extremely low, but say ~OEM-spec as opposed to max sidewall or higher) and compare again.