The summer travel season will soon be upon us and that means more cars on the road in Maine. This brings us to a reminder that bears repeating: The left lane is for passing while the right-hand lane is for travel.

Every state has restrictions on traveling in the left lane of a divided highway. Maine is among 11 states that forbid use of the left lane for anything other than passing on major roads, such as the interstate. Maine’s left-lane restriction applies on roads with speed limits of 65 mph or higher. “An operator driving on a limited-access way with a speed limit of 65 or more miles per hour is restricted in ordinary operation to the right-hand lane and may use adjacent lanes for overtaking and passing another vehicle, but must return to the right-hand lane at the earliest opportunity,” the law states.

If there’s an emergency vehicle in the breakdown lane on a divided highway, such as Interstate 95, then drivers should temporarily move over to the left lane. That’s state law, too.

Staying out of the left lane except to pass isn’t just about courtesy, it’s also about safety. Traffic, especially on interstate highways, is meant to flow smoothly. A vehicle traveling more slowly than others is a major hazard because drivers will navigate around it.

Here’s the science behind it. Variations of speed among cars on a road — not high speeds on their own — are more likely to contribute to a crash. In other words, a car traveling much more slowly than the rest of the vehicles on a road, especially in the left lane, is more likely to cause a crash than a car traveling in the left lane at a high rate of speed but generally the same speed at which all the surrounding cars are traveling.

The slower car backs up vehicles behind it, causing people to brake and change lanes more frequently. Both are more dangerous maneuvers than simply driving straight ahead. Lane changes cause as many as 10 percent of highway crashes.

Using the left lane only for passing also improves gas mileage because traveling at a consistent speed is more fuel efficient than accelerating after slowing down. Another byproduct of consistent speed is reduced road rage, the National Motorists Association says, because drivers behind don’t get angry at that annoying car blocking their way.

There are groups that have dedicated themselves to encouraging left-lane blockers to move on over to the right. One such group is America Keep Right, which has state chapters. A group called Left Lane Drivers has become a bit passive-aggressive in its approach — it sells windshield decals with the words “Move Over” and an arrow pointing to the right.

Passive-aggressive decals or tailgating or flashing your lights at left lane drivers won’t solve the problem. Instead, reminders on electronic highway signs and patrols by police are safer and more effective.

The problem is getting attention nationally. Several states passed laws last year to institute or increase fines.

The Virginia General Assembly passed a law last year instituting a $100 fine for misusing the left lane on that state’s roads. From July 1, 2017 to April 3, more than 16,000 people were issued citations under the new law, WTOP reported. The majority either paid the fine or were found guilty.

Other states are trying an educational approach. “Camp in the Ozarks, not the left lane,” was a message on an electronic highway sign in Missouri.

The message is simple, and reminders never get old: Pass in the left lane. Drive in the right.

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