I have a Garmin GPS and it has a couple of features that try to save you gas. They are ok, but they are not the greatest.
One of the features is the "ecoRoute." It estimates how fuel efficient you drive based off of how you accelerate/decelerate and your speed when cruising. When you are driving it will show you a number out of 100 to tell you how efficiently you are driving (100 being the most efficient). This is nice, but doesn't tell me anything I didn't already know. It claims that driving 60mph is less efficient than driving 65mph. I could be wrong, but I don't think that is right.
You can also set the GPS to a "less fuel" route, but it hardly is. Under this option it tries to keep you on roads with a 45mph speed limit (or there abouts) for the entire route as it can. However, that normally means it takes you on a route with more stops, negating the effects of driving slower.
I don't know if other GPS brands have similar things or what other people think of Garmin's system, but I don't think it's very useful.
I am highly suspect of the "less fuel" method they'd use.
I would *guess* that Garmin figures that there is some ideal speed (i.e. 40 MPH) and tries to get you on roads closest to that speed.
However if it doesn't consider the number of stop signs, traffic lights, the amount of congestion, and so on (which my Garmin doesn't, at least for the purposes of ETA which is why I'm always late), then it's gonna be useless or even counterproductive.
As an experiment, my wife and I found a much shorter route to church. Normally we travel about 25 miles each way, but we discovered a shortcut that brought it down to about 15 miles. However when we compared the amount of gas used, the "short" way was 1.6 gallons and the highway was 1.7 gallons (round trip). When you include the amount of wear & tear on the brakes and suspension because of the crappy roads, we decided to splurge on the extra 0.1 gallons and stay on the highway.
Does the Garmin have the option to show live traffic without a subscription on an ad-supported system? Does it help you route against traffic?
Yes, but this can also be kinda stupid. It will know the expressway is backed up but can't tell if the surface streets are also grid locked. Most of the time it gives good advice, except of course when you are running late for something important.
I have since only gotten one better tank, but when I set my Garmin to "least fuel" on a long trip, I got 47 mpg that tank. I have only bettered that just recently with a 48.9 mpg tank. On the trip to my destination, it basically just took me on old county highways that usually did not have too many stop signs, but would go through some small towns with 25-30 mph speed limits or a stop light/sign or two. It would also take you down some normal county roads that did tend to have more stop signs. That said, most of the roads I was traveling on had very little traffic. This meant that I could easily DFCO all the way to the stop without having to worry about impeding traffic or just neutral coast down hills, etc. I actually liked it because it was a MUCH more scenic route as well and on the 5 hr 30 min trip, I did not ever feel tired at all.
Now the downside... On the way there, for whatever reason it took me through downtown Lima. When I say downtown, I mean through the ghetto, with MANY stoplights (which were not timed, so you got stopped at everyone), heavy traffic, and even a train I got stuck waiting for. That was the only "problem" on the trip there. The return trip took me around the outskirts of Lima on a road that was very scenic and no stops at all, but at one point it did take me across ~ 2miles of GRAVEL roads. This pissed me off to the point that I switched the setting back to fastest time until I got closer to home.
That is my experience. I would only use it on longer trips, have tried it around town a few times and as mentioned, it will definitely not help FE on short, in town trips.
so in other words, it's only helpful outside of towns and if you aggressively hypermile (DFCO as much as possible and the like)
I don't have one new enough to have the ecoroute option but i like the old ones better. I used a Garmin IQue 3600 (Palm PDA based circa 6-7 years ago) for work which was great and the timing was very accurate, or I showed up slightly early. that one wasn't mine so i couldn't keep it. now I have a Nuvi 205....for the life of me I cannot beat the original ETA. Doing 5-10 over would get close but not quite make it. if there were any lights, stop signs, traffic: forget it.
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I think one thing to consider, is that the "less fuel" route may not necessarily be the "highest MPG" route.
For example, when I leave work there are 2 or 3 ways I can go. I usually take Sterling Boulevard home, and there are traffic lights every 1/4 mile. This route is about 2-3 miles, and the maximum speed limit is on Sterling Boulevard is 35 MPH.
I can take the Fairfax County Parkway to the Herndon Parkway, which intersects the street I live on, and the speed limit on that route would be 50 MPH. However, this route is about 6 miles.
It is faster, and uses less fuel overall for me to take Sterling Boulevard, and to wait at the traffic lights, than to take the higher MPG route, and travel twice as far.