I did an experiment during my commute yesterday – I tried to see how my gas mileage would be affected by just slowing down.
I remember in the 1970’s when the national speed limit was reduced to 55 MPH during the energy crisis. I also remember how much this p*ssed me off – I even got some speeding tickets going above 55 MPH but below 70MPH – they called it “an Energy Speed Violation” – I called it government intrusion into citizen’s private matters. I was pretty young so it made me so mad that I took up flying single engine planes because airplanes did not have what I considered to be a silly and pointless 55 MPH speed limit – I never checked gas mileage :).
So yesterday – I was not in a rush for my 55 mile commute so I decided to set the cruise to 55MPH and see what happens. I have a totally cool Buick LeSabre that gives me instant feedback on my mileage – it may not be perfect – but it is suitable for A-B comparisons.
My car is rated for (and usually gets) about 29-30 miles per gallon – this is pretty cool for a nice comfortable quiet car – that is even with the air conditioning on. SO it is not too bad of a commute car – particularly because it has low maintenance and is nice and solid in case of an accident.
So back to the experiment. The first thing I notice while driving 55MPH is that *everyone* is driving faster than you. Even the semi trucks give you a dirty look when they go around you – because you are messing up the cooperative traffic flow that prefers 62-72 MPH in crowded conditions. I did this experiment at 7PM so traffic was less than during rush hour – but I still was a problem and at times I caused a bit of a back up ad a truck passed me and the rest of the left lane had to slow to 62 MPH behind the truck.
The other nice thing about 55MPH was that I never had to change lanes – I putted along in the right lane and never had to even engage my brain about how to drive – everyone else had to go around me – I felt like a grandpa – not very cool at all. But this was for science – looking like a Grandpa is a necessary sacrifice for science.
So after 35 miles on cruise at 55MPH my car reported an average of 41 MPG! This is a 40% increase in gas mileage just by dropping 15 miles per hour! I was starting to feel a bit like a Prius.
I also did a simple less scientific test in our Subaru Tribeca (a small SUV) and found that gas mileage went from 18 MPG to 25 MPG by dropping from 70 to 55 MPH. Again about a 40% increase in gas mileage. I will do more testing and a bit more scientific.
Experiment detail: This was using cruise control – you can play games like coasting, drafting and careful throttle control up and down hills – to get even better gas mileage – I did not do any of those things. I was interested in something simple that required no particular skill – so I just set the cruise to exactly 55MPH and let the trucks and traffic flow around me.
Effectively by dropping down 15 MPH, you increase mileage by 40% – which is like getting a discount on your gasoline. This makes my $4.00 gasoline effectively $2.85 – at a cost of some more time on the highway.
This is a a way that we can drop our demand for fuel overnight – I kind of understand now why in the 1970’s they simply lowered the speed limit to 55MPh. I have a bad feeling that someone in government will see this and drop the speed limit – this will tick me off – particularly when I am late going to the airport.
So just for yucks – try to see what it would be like with a national 55MPH speed limit – for as long as you can (yesterday I did it for an hour and it was mind-numbing) – set your cruise for 55MPH – if you have a little info gauge – reset your fuel economy average at the beginning of the experiment and see what gas mileage you get. I reset it while I was warmed up and up to speed – I wanted to measure only the highway mileage. I was pretty surprised at what I got – you may be too.
Update: Just to be scientific – I repeated the experiment on the inbound commute and the results held – the inbound MPG for 55MPH was 41.4 on one leg and 42.4 on the other leg.