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Around the internet, people say a lot of dumb things about driving slow to get better mileage. Some recommend just driving the speed limit. Others say to drive a certain speed, like 55 MPH or 60 MPH, for best mileage. Others say to vary your speed depending on terrain (and they’re partly right there). But you also have to think about the other cars on the road.

The truth is, low speed can be more dangerous than high speed. Because of this, finding the best speed is all about striking a balance between safety and savings. There’s no set speed to aim for because every situation is different.

The safe speed varies.

This chart shows the combined results of six studies on the topic over decades. If you look at the middle of the chart, you’ll see where the line dips to its lowest. This is the average speed of traffic, and it’s where your chances of being in an accident are statistically the lowest.

The average speed of traffic has little to do with the speed limit. To know the average speed of the cars around you, you have to observe the flow of traffic and make that judgment call.

The flat yellow line shows where average accident chances are on the graph (1.00).

Within the green part of the line (from about 5 MPH below average to about 6-7 MPH above average), your chances of being in an accident are below average. If you go slower or faster (the red lines), your chances of being in an accident are higher than average and your risk rises more quickly going slow than it does going fast, so you have to use caution when slowing down to increase mileage/range.

Traffic Conditions vs Speed

The above chart has another limitation: it averages the accidents vs speed for every accident. It didn’t account for heavy or light traffic, or weather.

To illustrate this, I’ll give two extreme examples: bumper-to-bumper traffic and a lone country road at 3 AM. In bumper-to-bumper traffic, you can’t vary from the flow of traffic at all without risking a collision. On a long-straight road with no traffic, you can drive whatever low speed you want (within the law and in good weather, of course) without seriously risking getting rear-ended.

Most situations you encounter on the road will be somewhere in between these extremes. To pick your speed, you’ll need to use your judgment and decide whether other drivers are likely to see you in time and go around you. Keep in mind that other drivers may be drunk, sleepy or distracted.

If you are going a low speed (45-55 MPH) and people are repeatedly rushing up behind you, this is probably not a safe speed and you’ll either need to go faster or choose a different route with lower speed limits. If you are noticing that cars are only slowly approaching, you might be able to slow down some to save gas.

Finally, conditions change. If an empty rural road leads you into a city, you’ll have to drive differently to stay safe. When driving below the speed of most other drivers, you are responsible for keeping your eyes open to changing conditions and adjusting your speed up as needed. Sure, they may be legally responsible if they rear-end you, but do you really want to get in a wreck??

There are no rules of thumb here. You have to exercise good judgment and pay attention to safely go below the flow of traffic.

Don’t be a jerk!

Finally, you should be considerate of other drivers to stay safe and legal. Be a decent person and do the right thing.

In many places, you are required to pull over to the side and allow faster traffic to pass when going slow. Clogging up the road creates a public safety hazard and you can be fined for it. Get out of the way or speed up to avoid creating a traffic jam.

There’s also the problem of road rage. Sure, you’re not at fault legally speaking if somebody gets mad at you for driving too slow and does something stupid. But do you really want to put yourself in that position? Is it worth the risk to yourself, your loved ones or your vehicle? Don’t be a smug jerk. Swallow your pride and stay alive.

Finally, it’s just the right thing to do. Other people are in a rush to get places. Their jobs, their relationships and other important things might rely on getting there on time. Sure, you planned ahead to go slower and save gas, or you’re in no rush. But that doesn’t mean everybody else was planning on going below the speed limit. Do the right thing. Get out of the way.

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