Why do we have to slow down to a crawl on the freeway?

Here’s another helpful infographic for all to ponder. Ever been hightailing it on the freeway when all of a sudden brake lights start lighting up like the Griswold house around Christmastime and you wonder why in the heck everyone has decided to slow down? It’s called a shockwave by traffic planners and it affects just about everyone at some point in time.

It starts off when one driver takes a bit too long to get into their lane or when something in the road catches their eye and they slow down to see if they should swerve or run over it. That minor change in one driver’s pattern begins a ripple effect that affects everyone behind them. All of a sudden, that driver is going 5mph slower than they were, making the person behind them slow down by 10mph to keep a safe driving distance. The more cars involved in this effect, the slower they have to drive to adjust to the change in flow. By the time everyone reaches the point where the original driver slowed down just a bit, there is no evidence as to why the change occurred and angry drivers chaulk it up to rubbernecking or bad driving.

It’s comparable to water flowing through a funnel. A slow drip flows smoothly down and exits freely; add a sudden rush of water and that funnel is now filling up and spilling over. Just something to think about next time you’re out on the freeway and are convinced some idiot just ruined your day.