When other Prius drivers ask me why my gas mileage is 10 MPG higher than theirs, I usually reply with this question: “How fast do you drive on the highway?”
It should come as a surprise to no one that higher cruising speeds require more fuel than lower cruising speeds. A good rule of thumb is that every mile-per-hour above 55 will set you back a mile per gallon in terms of fuel efficiency. This applies to all cars, not just the Prius, but the Prius particularly excels in lower-speed highway driving. Earlier this year, driving from work to the airport to pick up the in-laws, I finished the 40-mile highway trip (210 East to 605 South to 105 West) at 64.8 MPG. When my baseball games take me deep into the Valley, requiring 20 or more miles along the 134 and 101 freeways, the consumption screen’s 5-minute interval bar graph rarely dips below the 75 MPG mark.
The appeal of dropping your highway speed will depend on the length of your commute. Mine is about 8 miles each way, so the difference between going 70 and going 55 works out to only a four minute difference in travel time, round trip - less than 20 minutes a week. But even if you have a 20-mile commute, an extra 15 miles per hour will only cut your travel time by less than five minutes each way, while costing you an extra $300 in gas over the course of a year.
Even I have my limits, however. While driving out to Las Vegas two weeks ago (a 240 mile trip each way), we drove 85 MPH the whole way - and averaged just over 42 MPG for the trip. I’m not that interesting in turning a 3-½ hour trip into a 5-hour one just to prove a point!
A secondary advantage to a lower highway cruising speed presents itself when highway traffic slows - as it so often does where I live. Driving 55, I rarely have to hit the brakes to slow for traffic - the slower speed allows me to react to brake lights ahead by laying off the gas (or, more typically, disengaging the cruise control) and coasting, taking full advantage of the Prius’ regenerative braking system. Were I driving 10 or 20 miles per hour faster - and likely trailing the car ahead of me much closer - I would have to engage the brakes, wasting all of that potential energy that could have gone into the batteries.
* * *
If you’re only going to follow one piece of advice presented here, let it be this: ease up on that accelerator. Dropping your typical highway speed from 75 to a-still-above-the-limit 70 miles per hour will boost your highway MPG’s by 4 or 5 — and more is even better. When you do the math, speeding really doesn’t get you there much faster anyway.
Bonus tip: set the cruise control whenever traffic allows. The car’s computer is much more efficient at maintaining speed than you are.
How good is the highway from LA to LV? Is there a speed limit and if so what is it? 85MPH sounds very fast from a safety viewpoint. Here, the speed limit is at most 110kph, about 68mph.
BTW, presumably your advice applies to all cars, not just hybrid cars.
By: Rodney on May 29, 2007
at 6:26 am
Yes, this advice should work just as well for traditional cars, although chapters 4-6 (upcoming…eventually) will focus on hybrid-only tactics.
85MPH was faster than 90% of the cars on the road, but not an unsafe speed - I-15 between LA and Vegas is a well paved, mostly-straight limited-access highway, without much traffic when I was driving.
By: Rattling the Kettle on May 29, 2007
at 1:04 pm
This advice is good but a little outdated, with more highways setting their speed limits at 70 mph. I am looking at buying a Prius as my next car, which is why I read this article. The EPA and car manufacturers need to update their calculations for gas mileage to account for the fact that many highways have 65 or 70 mph speed limits now.
By: Melissa on June 25, 2007
at 10:02 am
Off the subject just a bit…We’ve been told that the Prius gas mileage starts to improve after 10-15,000 miles has been driven. Anyone know why this modern car has to be “broken in” to see this improved mileage?
By: jim on January 20, 2008
at 8:46 am
I suspect it’s the driver, and not the car, that needs to be “broken in”.
By: Rattling the Kettle on January 20, 2008
at 9:18 pm
