Why do they make roads that cause porpoising?

free radical wrote:

mkirsch wrote:
Just got back from the "big" camping trip of the year.

The last 5 or so miles on the East end of Interstate 490 in New York is fairly new concrete. My truck is nothing special, a regular cab long bed with the most common pickup truck wheelbase on the planet.

I have to drop down to 50MPH on this stretch of highway to keep my head from bouncing off the cab roof! Doesn't matter loaded or empty, it bucks like a bull moose in heat.

If I maintain the 65MPH speed limit, the truck quickly becomes uncontrollable. It's downright dangerous. Even my DD gets to galloping on that stretch of road.

If my truck does it, EVERY regular cab long bed that passes through there has to be experiencing the same thing. It's a function of wheelbase and the seams in the road.

Hundreds of trucks like mine, maybe thousands, pass through that area every day.

Why on earth would the DOT spend millions to lay down a road that they *KNOW* is going to set up such a dangerous harmonic?

Ive experienced the same problem in Edmonton on Anthony Henday dr ,and its brand new concrete surface!!
I figured its probably those gaps are made wide on purpose so the concrete can expand and contract,as the temperatures can vary from minus 30 in winter to plus 30 in summer,,
but since its only small section of that road its probably some design fault ..

That's strange with the Henday Jr. I know a few people on that project. Experienced with concrete paving too. Not sure what the cdn hwy spec is for control it placement though.
Fact of the matter is concrete moves, swells, shrinks, edges swell more than the mass.
It can be controlled by proper jt placement to a great extent but concrete is still a science experiment.