Those long car rides are incredibly boring, yet your penis is standing at attention. What gives?

The erections you pop while on a long car, bus, or plane ride is actually pretty normal. And it’s because you’re basically planting your perineum on a giant vibrator.

As the vehicle’s vibrations travel to your seat, they stimulate nerves at the base of your penis.

This activates your parasympathetic nervous system, directing blood to your penis, says Thomas J. Walsh, M.D., a urologist and the director of the Men’s Health Center at the University of Washington.

At the same time, something else is stimulated: your imagination.

“When you spark this nervous system, you may also activate pleasure sensors that can back-feed and trigger sexual arousal,” Dr. Walsh says.

Both of these factors can help you pop a boner.

Related: The Men’s Health Complete Guide To Erectile Dysfunction—the Only Resource You Need For Your Most Pressing Penis Problem

So what do you do when you reach your destination and need to avoid an awkward exit?

Dr. Walsh suggests giving your inner thigh a firm pinch. Pain triggers nerves that will make your erection evaporate.

The Editors of Men's Health The editors of Men's Health are your personal conduit to the top experts in the world on all things important to men: health, fitness, style, sex, and more.

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