Don’t like traffic jams, Minnesota? Drive differently

There’s not a lot of new in today’s Minnesota Department of Transportation report on congestion on metro-area roadways. It’s getting worse, as anyone who’s tried to get anywhere on metro-area roadways can attest.

But one of the reasons it’s getting worse — aside from there being more cars — is the habit of drivers who contribute to the shock wave effect.

You can find it during any rush hour. In my case, I find it usually on Minnesota Highway 52 out of St. Paul on the top of the bluff, and on Interstate 94 on the tight left corner on the east side.

Why does traffic slow to a crawl, then suddenly speed up when there’s nothing in the road to account for the sudden stall?

It’s the “shock wave”, according to MnDOT and it usually happens when cars get to around 45 mph.

A shock wave is a phenomenon where the majority of vehicles brake in a traffic stream. Situations that can create shock waves include:

• Changes in the characteristics of the roadway, such as a lane ending, a change in grade or curvature, narrowing of shoulders, or an entrance ramp where large traffic volumes enter the freeway.

• Large volumes of traffic at major intersections with high weaving volumes and entrance ramps causing the demand on the freeway to reach or exceed design capacity.

• Traffic incidents, such as crashes, stalled vehicles, animals or debris on the roadway, adverse weather conditions and special events.

Drivers’ habits can also contribute to shock waves. Drivers’ inattentiveness can result in minor speed variations in dense traffic or sudden braking in more general conditions.

In these situations, shock waves move upstream toward oncoming traffic at rates varying according to the density and speed of traffic.

As the rate of movement of the shock wave increases, the potential for rear end or sideswipe collisions increases. Multiple shock waves can spread from one instance of a slowdown in traffic flow and blend together with other extended periods of “stop-and-go” traffic upstream. This condition is referred to as a “breakdown” in traffic.

Usually breakdowns last the remainder of the peak period if traffic volumes are close to or above design capacity. These types of breakdowns are typical in bottleneck locations on the freeway system.

This is how it happens:

There is a cure for this sort of phantom traffic jam. William Beaty, an electrical engineer, figured it out in 1996 and started

As with most things in traffic, the solution will make other drivers around you mad — it’s to drive slower, the BBC documented.

Beaty’s methods (which, really, boil down to “be nice, and don’t be in a hurry”) are catching on with some drivers, though it’s impossible to say just how much of an effect they’re having on your daily commute, since things like GPS navigation, increased load, and adaptive cruise control must be factored in as well.

Beaty is hopeful that drivers-ed teachers will add his theories to their curriculum, but he knows his biggest obstacle is drivers themselves, and their obsessive need to be somewhere sooner.

It makes perfect sense, really, and you’ve probably seen truckers do it, leaving plenty of room to the car in front, at least until people in a hurry to stop up ahead fill in the gap and cause a shock wave.

Eventually, once automated cars catch on, the biggest problem causing traffic jams — humans — will be eliminated.

In the meantime, try Beaty’s approach this afternoon. Especially if you’re on Highway 52 or I-94 on the east side.

  • MrE85

    The US Dept. of Energy estimates that idling vehicles waste 6 billion gallons of fuel every year in the USA.

    • Rob

      Idle motors are the devil’s playground.

  • 35 MPH 6-8 second following distance

    Follow these guidelines and it’ll help reduce your time smashing on the brake pedal. At least that’s what my professional driving instructor taught me…

    • Veronica

      That’s what I learned, too. I’m pretty strict about it, not just because it’s safer in general, but if I get rear-ended (which happened in traffic on 77 S last December), I probably won’t be the middle of a car sandwich.

    • Rob

      Yes! It’s virtually impossible to rear-end someone when you have a safe following distance. Also, it drastically reduces the likelihood of being the victim of a rear-end collision. And when you go the speed limit on the freeway, you reduce the likelihood of being tailgated, as speeders coming up behind you quickly discern you’re traveling at a slower speed and thus will generally go around you.

  • Jeff R.

    Unfortunately – traffic, like nature, abhors a vacuum.

    • MrE85

      Our dog used to hate them, too.

      • tboom

        From my experience, cats too.

    • Mike Worcester

      Traffic (read — human drivers) also abhor extra space between vehicles and rush to fill them at breakneck speed :

  • Fact Proofer

    Mr. Beaty describes precisiously why MNDOT’s Zipper merge for construction does not work. Waiting until the last minute to merge causes the entire traffic flow to slow and/or stop. If the merge occurs earlier, as Mr. Beaty has discovered, the traffic flows smoothly with little inturruption. Other states have discovered this toe the extent that Illinois tells drivers to Maintain contruction speed limit (not slow down as many want to do) through the construction zone. This allows vehicles to maintain the space Mr. Beaty advocates and traffic never becomes jammed.

    • Jay T. Berken

      That is the one problem I had with his video, the ‘cheaters’. He alluded to it, but if people would allow to merge, you do not have the backup. Why have the lane if people are not going to use it! ALLOW THE MERGE.

    • Nathan

      What!? This is not my experience with zipper merges at all. If drivers merge way ahead of the merge point with heavy traffic all it does is create a much longer line in one lane leaving a whole host of wasted pavement in the second lane. If people simply drove a little slower and took turns at the merge point there wouldn’t be any problem. There’s a very annoying passive aggressiveness in Midwestern driving when it comes to merging, anywhere, whether it’s at a zipper merge or on/off ramps with drivers not leaving room, speeding up to eliminate room for merging cars, or even blocking lanes.

    • Jeff

      In defense of the zipper merge, it can reduce congestion by 40% If people did allow a gap then I see your point, but often times it’s people who stop and wait for someone to let them in that gums things up.

    • Ben Chorn

      It’s pretty laughable that anyone would expect Illinois drivers to follow any speed limit.

  • PaulJ

    so, are cars waves or particles?

    • Jay T. Berken


    • Jeff

      Entangled particles – spooky action at a distance.

    • jon

      The important thing is to acknowledge they have mass.

    • Alex

      Particles through which waves can form.

  • Jay T. Berken

    I agree with this. I took a hydrology class in college, and one of the units was about waves where every wave starts at the same point due to an obstruction (i.e.change in sea floor especially if there is an underwater ‘break wall’). Anyway, through my commute, I have noticed that if you can see in the distance a stopping point of cars, I try to slow down to try not to use my brakes. Brake lights are contagious, I people see them, they use them. I have been using the allow car lengths in from of me, aka swallow my pride, and allow cars in. One of my peeves about commuting, besides the brake lights phenomenon, is not allowing cars to emerge, seriously let people in. I take Hwy 5 across the Mississippi River under Fort Snelling and when coming up to the Hwy 55 ramp merging, I allow 2 to 4 cars merge and watch the magic of the traffic loosening up.

  • Rob

    The zipper merge is both useful and enjoyable as an activity among consenting adults; as a traffic management concept, it sucks.

    • Postal Customer

      And since 95% of Minnesota drivers either cannot or will not engage in the zipper merge, I benefit from that fact. I’m happy to speed ahead of the column of parked cars. There is perhaps no better example than the lane from eastbound I-394 to eastbound I-94 right around Dunwoody. People happily get in that line, a mile long at times, and sit and sit and sit. I fly past them and merge at the last moment possible. It’s gotta save at least 10 minutes in some cases.

      My friend got irate at me once for doing this. “You’re not waiting your turn.”

      I told him, “You don’t get bonus points for being stuck in traffic.”

      • Dan

        That’s not exactly two lanes merging into one, as in the case of a lane closure for construction. People frequently are slamming their brakes in the middle lane to cut over to the 94-Eastbound lane, in front of people who are going to 94 Westbound. That creates a whole other situation between 94-westbound traffic (swerving out of the way) and the downtown lanes.

        People also frequently cross the double white lines, I suppose considering that “at the last moment possible”, even stopping in the middle of the westbound lane. That in particular (not accusing you) isn’t what MNDOT is asking people to do. I really wish they’d erect concrete barriers instead of the double lines there.

        Not a particularly well designed junction, but I suppose they had some interesting constraints to work with re:394.

        But, you’re hardly the only one cutting over at the last second. I’m not sure that’s exactly helping traffic, people cut over pretty aggressively there, which leads to chain-reaction brake slamming.

  • Ben Chorn

    As mentioned, my biggest problem with trying not to hit my brakes in a traffic jam is trying to leave enough space where I can coast but not enough that someone thinks they should cut me off. I find it’s usually easiest in the 2nd to left lane since people in the left lanes always seem to have some kind of entitlement

    • jon

      In the car, try not to hit the brakes for slowing down, but aware of who is behind you and be willing to use the brakes to signal them that you are slowing down.
      On my motorcycle try to not put my feet down, use the brakes to signal every slow down so people will actually see me as opposed to plowing through me.

  • mattaudio

    When I clicked on a link titled, “Don’t like traffic jams? You can eliminate them anytime you want,” I expected to read about how people are free to move closer to their jobs or find a job closer to their home, and avoid car commutes on freeways altogether.

    • Not everyone who’s stuck in traffic in on their way to/from work, though. Funny think about the interstate highway system.

      • mattaudio

        I can no longer find the links, but a nationwide study showed that something like 94% of people “stuck in traffic” on freeways in major metropolitan areas (obviously during “high traffic” periods) are mobility routines that occur at least three times a week in the same timeframe. To summarize, it’s nearly all people commuting to work/school/etc as part of a frequent routine.

        • So we need another recession. As I recall that was credited for a reduction in traffic jams in ’09.

          • mattaudio

            If 5-10 percent unemployment makes our freeways nearly free-flowing (which jives with other data I’ve seen about the marginal effects per driver on freeway level of service), then it also reasons we could significantly reduce congestion if 5 or 10 percent of people simply moved closer to work or got a job closer to home, where they didn’t need to commute via freeway.

            Personally, I think a healthy economy would do just as much as a recession in terms of freeway LOS. This is because people have more jobs available in more fields of work, so there’s more of an opportunity to escape a miserable commute. Right now, people are stuck in awful commutes because they had to take what they could get when the going was tough.

          • This collides with my consternation of how much people’s lives are defined but what they do for a living.

            It must also define where we live?

          • Carlton Schaps

            Many people haven’t recovered from the previous Depression so let’s not try that one.