Heat and buckling roads

I am wondering why we are hearing of and seeing pictures of roads and highways buckling in the heat in the midwest and northeast.

Even though a few places are feeling a heat index of 112 or so, here in Arizona we have temperatures in the shade of 112 and higher almost all summer.

I have yet to hear of any road buckling hereabouts. What are engineers in the north not doing that causes such a phenomenon?

The roads, in the Mid-West and NE are built to withstand ice(to a degree). Large expansion joints which permit movement would allow water in and freeze during winter resulting in cracks and worse. All over the country we use different building practices for different environments, here in South Texas on the rare occasion that it freezes it is a disaster for the roadways. Some of the greatest differences I have seen are in bridge design, here we pour bridges over pre- stressed concrete supports, easy and cheap but they freeze in an instant and are basically unusable below 32f. I am no highway engineer so I am sure there are more technical details to come


Probably what engineers in Arizona don’t bother doing to prevent roads falling apart because of temperature swings of 145 Fahrenheit degrees — from –40 to 105 — in Canada and the northern states.

If Arizona experienced –40 temps as regular occurrences, it would take years if not decades before all the state’s roads could be rebuilt to handle such extreme swings.

Speaking of buckling, what are those humps on interstate blacktop that form over time called? Almost like a “wrinkle” in the road? I notice them for awhile because its jarring to drive over them but then at some point I notice they’ve been scraped (graded?) off and there’s just like a patchy area there but the mini-speedbump is gone.

What causes that? Heat?

I can only assume it is heat, sometimes when it has been hot here the Asphalt will get a little soft. We need an engineer here.


My guess is you’re seeing reflective cracking. The roadway was originally concrete and was later overlaid with asphalt. Over time any cracks in the pavement, as well as the old joints, will show through to the surface. Now you have a crack in the road and as the pavement cools the crack widens, letting in dirt, and when it heats it expands, but the crack can’t close because of the material that’s fallen in so the asphalt is pushed around.

Nitpick: All official temperatures are taken in the shade.

Here in Minnesota we might have a dozen terribly hot (above 90 F.) days in a normal summer, and that’s when we see road buckling. We sometimes have 4-5 months where temperatures fall below 32 F. It only makes economic sense to build our highways to withstand the latter, since repairing the buckles is relatively inexpensive.

Are there several bumps or just one? If there are several in a row, it’s called washboarding and is due to vehicle’s suspensions bouncing up and down slightly. When the bounce downward, they exert more force on the road and create indentations over time. Once a small dent occurs, other vehicles bounce in that same spot and make it worse faster.

I don’t think its reflective cracking. The images of that online I looked at are showing me actual depressive cracks in the road surface. The things I am trying to describe are actually “raised up”…they look like mini speed bumps…only narrower. And Fubaya, I do think they are in a pattern, forming along what I must assume are the pavement expansion joints. And I will see them for awhile, and then at some point they get scraped off the road surface.

A press release from DOT said that the cause of pavement cracking in extremely hot weather is moisture that has seeped into the cracks, expanding.

I don’t buy this for a minute, especially when we have had no precipitation for weeks. If a liquid in a crack were to expand, it would just expand its way back out the way it came in, would it not? Ice I can understand, but not liquid water.

I think the most likely scenario is simply that the road surface itself is expanding enough to close up expansion joints, and then when it has nowhere else to go, it buckles.

It makes me wonder if there’s a DOT engineer head-smacking somewhere at the press release created by a PR person :smack:

Is that really true? Thinking about it I would assume it’s the upward bounce that puts more pressure on the road as you get back the stored energy in the suspension.

Cecil confirms it.

(It happens around here on ashphalt freeways in the two right lanes that the trucks are required to use. Not as bad as on gravel/dirt roads.)

The ones that run across the road are often from the concrete slabs that form the road (which may be concealed under asphalt) shifting. This was particularly common in areas of high truck traffic. How annoying it gets depends on both the amount of the shift as well as the relative spacing between slabs compared to your vehicle’s wheelbase. I have an unusual car which happens to have the same wheelbase as a commonly-used slab size. This sets up a vibration similar to riding a galloping horse - very unpleasant.

In the “old days” the solution was to completely remove the concrete and rebuild the roadway - paving over it would only help for a brief time. The current mitigation strategy is to cut (normally) 6 slots in the concrete, 3 on the left and 3 on the right, and insert rods to tie the slabs together. The surface is then ground smooth and optionally paved. See this Wikipedia article on “dowel bar retrofit”.

Ruts / bulges that run lengthwise down the road are from the weight of vehicles displacing the asphalt paving material. New York City normally uses concrete for the road at bus stops, even on asphalt-only roads, to prevent sitting buses from causing this.

It can still be reflective cracking. The pavement cracks, material gets in, and when the asphalt expands it can’t close the crack. The only direction for the pavement to go it up, so it humps. I’ve seen it before.

Here’s a picture of an airplane stuck in a soft spot on the tarmac at Reagan Airport.