Have others noticed the difference that road surfaces make? When I drive on the expressway (55 - 60 mph) I get about 45 - 55 mpg according to my instantaneous gauge. The surface is poured concrete and in very good condition. However when I'm on local two lane roads at about the same speed I get at least 5 mpg less. These roads are asphalt, not as smooth with more imperfections.

Makes sense I guess, just wondering if others find this too.

 

I found that a stretch of road, moderately down hill, of about 1.75 miles, became on clear, coast after paving. Before it was repaved, I would always need to engage the ICE in them middle part to maintain 45 in a 50 mph zone.

Smooth pavement = high mpg.

 

One of the design std's for building the interstates was a road surface friction factor. The smoother the surface = better mileage but less traction under certain conditions. You could probably do a google search for the particulars on this. I don't think the local roadways have such std's but I may be wrong.

 

I drive from Houston to Columbus, TX for work each day (75 miles one way), and there are a few good routes I can take to get there. One route takes me on interstate 10 and I have been getting about 42 MPG that way, the other route I typically take is down HWY 90, and it is a two lane asphalt road with some cruddy surfaces. Some stretches that have placed an overlay by spraying tar and dropping gravel over it. The mileage on this road has been about 37 MPG, so the surface can have a huge impact.