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## Daily (Intermittent) Open Ended Puzzle [DOEP]: Optimal speed

Thirty years ago, we were told that we should drive 55mph (or, in Europe, 42 euros per hectare) on the highway because that was the “optimal” highway speed when it came to squeezing miles out of gallons.

What is the current optimal highway speed?

And, for extra credit, what is the optimal speed on or off the highway? If I want to get maximum miles per gallon but don’t care how fast I go, how fast should I drive? Two caveats: Yes, I know this will be different for different cars in different conditions. And, no, zero mph is not an acceptable answer, no matter how true it is.

### 6 Responses to “Daily (Intermittent) Open Ended Puzzle [DOEP]: Optimal speed”

1. Have you ever been spread free printable trivia quizzes using the Trivia Questions database ?

2. The best way to get good MPG is to drive to minimize use of your brakes (unless you have a Hybrid with regenerative braking). Stop doing the drive a great speed to next light, slam on brakes, stop, wait, repeat.

3. Even if you have regenerative braking, it’s the most efficient to never use the brakes, or for that matter, the battery assist. (The regeneration is less than 100% efficient). In a situation where braking is unavoidable, then regeneration definitely helps, though.

In a Prius, the optimum MPG probably happens between 20 and 40 MPH. Smoothly accelerate up to 40 (the top speed at which the engine will completely shut off while coasting), then coast down to 20 MPH or so. Repeat.

(As it happens, this is also the maximally annoying way to drive. Only recommended on a narrow road with no passing zone when there’s an H2 tailgating).

The acceleration part can probably be done in 15 seconds getting 40 MPG all the while. The coasting part can probably last for 45 seconds on a smooth, flat road getting infinity MPG all the while. Net is well over 100 MPG.

There’s no reason why this couldn’t be done on a non-hybrid vehicle, but it would be more work, starting and stopping the engine, shifting into and out of neutral, etc.

-m

4. Can I formally object to the dig at the metric system in your post? Quoting car efficiency in litres per 100KM actually makes a lot more sense (although here in the UK we buy our fuel by the litre but measure distance in miles)

5. Mr. King:

Your objection is formally acknowledged and has been forwarded to the Assistant to the Undersecretary of the Minister of Objections.

Let the record show that the remark in question was intended as a dig at American incompetence when it comes to measurements other than our own arcane, irrational systems. Let the record show that I favor America adopting the metric system with an ardor (or, ardour, if you prefer) that in other circumstances would require having completed one’s marriage vows.

Yours in decimals,

David

6. Since NZ is decimalised I respond thusly.

The optimal speed in city traffic is probably close to 15kph given that traffic jams occur because of the exogenous factors such as traffic lights, idiots cutting in etc. The point being that you should drive at a speed which allows the vehicle to keep moving at all times and since the average speed of city traffic is probably about that (your city may vary) it would be a good guide.

On the open road or highway, the optimal speed is closer to 80kph (50 mph) than 55 because above that, some Citroens and other highly aerodynamic vehicles aside, air resistance becomes exponentially a greater factor than all other conditions.

I have tested this in driving from Nelson to Auckland, a distance of about 750Km using only 40 litres of fuel. (And yes, I know about cook Straight, I took a ferry and didn’t count the distance)

By sticking to 80kph the journey was occasionally made unpleasant by passing, or unable to pass, motorists but I’m now confident that I can get 800kms on my 45 litre fuel tank.

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