# What causes asphalt to ripple at intersections? **URL:** \ **Category:** Factual Questions\ **Created:** [January 10, 2006, 10:10pm UTC](https://boards.straightdope.com/t/what-causes-asphalt-to-ripple-at-intersections/339386 "2006-01-10T22:10:06Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Kitchen\_Wench](https://avatars.discourse-cdn.com/v4/letter/k/f08c70/32.png) [@Kitchen\_Wench](https://boards.straightdope.com/u/Kitchen_Wench)\ **Post date:** [January 10, 2006, 10:10pm UTC](https://boards.straightdope.com/t/what-causes-asphalt-to-ripple-at-intersections/339386/1 "2006-01-10T22:10:06Z")
This has perplexed me for a good many years. I’ve noticed that the road is bumpy, or rippled, maybe five yards leading up to the stopping point at many local intersections. I haven’t gone out of my way to measure the height of the ripples themselves, but I have to drive off-center to avoid jarring my car at 35 mph with a green light. I’m sure it has something to do with the weight of frequently queued vehicles damaging the road over time. What is the mechanics of this? And why the ripple effect? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 10, 2006, 10:14pm UTC](https://boards.straightdope.com/t/what-causes-asphalt-to-ripple-at-intersections/339386/2 "2006-01-10T22:14:30Z")
The effect is called ‘[Washboarding](http://www.straightdope.com/mailbag/mwashboard.html)’ - the linked article talks about unpaved roads, but asphalt is soft enough for the effect to work on it too. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [January 10, 2006, 10:22pm UTC](https://boards.straightdope.com/t/what-causes-asphalt-to-ripple-at-intersections/339386/3 "2006-01-10T22:22:30Z")
During warm times of the year, the asphalt paving is softened enough to deform. When vehicles approaching the intersection are braking to stop, some of that energy is absorbed by the road surface, said surface being pushed towards the stop line. If you’ve ever stopped abruptly on an area rug which wasn’t rubber backed and had the rug ripple up in front of your feet, that’s the same thing, on a different scale. Over time, many stopping vehicles, particularly large vehicles, and hard stops will cause the intersection topography you’ve observed. ---
**Author:** ![Kitchen\_Wench](https://avatars.discourse-cdn.com/v4/letter/k/f08c70/32.png) [@Kitchen\_Wench](https://boards.straightdope.com/u/Kitchen_Wench)\ **Post date:** [January 10, 2006, 11:13pm UTC](https://boards.straightdope.com/t/what-causes-asphalt-to-ripple-at-intersections/339386/4 "2006-01-10T23:13:02Z")
Thanks, guys! > [@Staff Report](#): > > Washboarding is inevitable in any unpaved road that sees fairly heavy traffic. The only way to avoid it is to: (a) radically redesign how automotive suspensions are made, (b) give up suspensions altogether, or © keep off those dirt roads. Are there any better quality pavement materials that would prohibit the washboarding effect, or at least last longer than say, 5-7 years? I’ve heard that in some European countries, roads are designed and built to last decades longer than our roads here. Why the heck can’t we start doing what the Europeans do? ---
**Author:** ![xbuckeye](https://avatars.discourse-cdn.com/v4/letter/x/9e8a1a/32.png) [@xbuckeye](https://boards.straightdope.com/u/xbuckeye)\ **Post date:** [January 10, 2006, 11:32pm UTC](https://boards.straightdope.com/t/what-causes-asphalt-to-ripple-at-intersections/339386/5 "2006-01-10T23:32:16Z")
Washboarding is actually different from what you described in the OP. Concrete won’t ripple, but is more prone to breaking and is harder to repair when it does break. Pavement, like so many other engineered things has to walk a fine line between firm and flexable. Washboarding is more of a periodic compression thing where there is vertical, not horizontal deformation. If you went out and played in traffic to examine the road, you would see that there are cracks where the asphalt surface has been pulled apart. **danceswithcats** is right on target with the wrinkled rug description. ---
**Author:** ![Doug\_Bowe](https://avatars.discourse-cdn.com/v4/letter/d/df788c/32.png) [@Doug\_Bowe](https://boards.straightdope.com/u/Doug_Bowe)\ **Post date:** [January 11, 2006, 12:44am UTC](https://boards.straightdope.com/t/what-causes-asphalt-to-ripple-at-intersections/339386/6 "2006-01-11T00:44:00Z")
> [@Kitchen Wench](#): > > Thanks, guys! > > Are there any better quality pavement materials that would prohibit the washboarding effect, or at least last longer than say, 5-7 years? > > I’ve heard that in some European countries, roads are designed and built to last decades longer than our roads here. Why the heck can’t we start doing what the Europeans do? When my Father worked for a city in South Texas tbey had a particular problem with a stretch of street next to the bus station. If you think automobiles can cause problems with washboarding, think of hot South Texas Summers and buses. The city reached an agreement with the bus company to divert their buses a different route for one month. Then the city ripped up the asphalt of the street in question and poured in a block long (with proper expansion joints, of course) of cement. ---
**Author:** ![Chairman\_Pow](https://avatars.discourse-cdn.com/v4/letter/c/838e76/32.png) [@Chairman\_Pow](https://boards.straightdope.com/u/Chairman_Pow)\ **Post date:** [January 11, 2006, 5:02am UTC](https://boards.straightdope.com/t/what-causes-asphalt-to-ripple-at-intersections/339386/7 "2006-01-11T05:02:24Z")
> [@Kitchen Wench](#): > > I’ve heard that in some European countries, roads are designed and built to last decades longer than our roads here. Why the heck can’t we start doing what the Europeans do? That’s getting into IMHO, so you’re not likely to find an answer here. The general answers I get when I’ve asked this are: a) In Europe, the contracts are to maintian the roads for decades. Obviously, to make a profit, you can’t be going out there every year to resurface it. The roads are built better. b) In the US, the roads are maintained by the state and they don’t want to fire everyone, so it’s off to resurface again and again. c) Graft, corruption, backscratching agreements, etc. I’d like to see if anyone else has come to the same conclusions.