In a perfect world, it might be best to coast in neutral and never touch the brakes, letting the car get up to whatever speed it can - 140-160-180km/h - then coast on the flats until you get back to your 110 km/h, but between traffic and cops, that's not really an option.
Brakes are the worst. If you have to brake, go in gear first and use brakes as a secondary method of slowing down. If you don't need to reduce your speed or have to speed up (in the case of a downward incline), coast in neutral.
"I wasn't speeding all the time, officer." That works, right?
Check out ecomodder.com and cleanmpg.com, they have some hardcore hypermilers there. You may not incorporate their techniques (engine off coasting for example, yikes) but you get a sense of what works for them and try to mildly incorporate it in your driving. I used to drive from Mission to Coquitlam BC a lot and when traffic was not heavy, I would go down to 70, speed up to 98 (80 limit, 99% of the time in BC on the highway, cops will not bother going for speeding tickets up to 20 over), and then coast back down to 70, rinse and repeat. With that method, I would go on average 6.3 to 6.7L/100km in my Mazda 5 rated 8.1 L/100km highway. Going an average 80-85 all the way, I would do 6.7L/100km at best.
I rarely do this though because 1. It bugs my wife for me to gas coast gas coast gas coast, I would subconsciously do this once in awhile and she would tell me to quit it lol 2. I won't do this if there are cars behind me, 3. It takes a bit of brain power.
So the technique I use more is find a throttle level that'll keep me going at whatever speed on a flat then stick with it uphill or downhill.
