Educate me about Highway Guardrails

I’ve always been under the impression that guardrails are supposed to reduce injuries by keeping your vehicle on the road surface instead of in the woods, the river or the oncoming traffic in the other lane. Guardrails here in Maine are sturdy. The posts driven into the ground are similar to I beams and probably 6 to 8 inches wide. The rails themselves are about 12 to 14 inches high. It’s unusual for a passenger car to ever crash through one. Even many trailer trucks bounce off.

Last week I was driving through New York and Connecticut. Many of their guardrails use little posts - like the 2 x 4 metal studs used in interior office construction. And the “rail” itself has been replaced by 2 or 3 little strands of wire rope. From the dozens of gaps I saw, the ropes don’t hold too well. Seems more decorative than functional.

I had been under the impression that pretty much all aspects of highway construction were regulated by Federal standards.

What’s the Straight Dope? :confused:

It wouldn’t be have to be held to Federal standards unless it were a Federally funded road. Did you happen to notice, were these state or local roads perhaps?

All Interstate Highways I-81, I-84, etc.

Interstates are probably standardized, I couldn’t swear to. Even though I did work I-10 from Louisiana to Baytown. But since I haven’t worked on other interstates I have no comparison.
However, state highways (in Texas) aren’t what I’d call standard. There are state minimums across the state but regional requirements can vary from place to place.
I worked most of the southeast region of Texas and I can say from experience that specs changed depending on variables. Even though on average they were fairly consistent. Even a single road might sometimes change specs as we crossed county lines. (usually an upgrade)
Still, I think at minimum standards Texas has a pretty damned good set of highways.
I can’t say that I recall anything like what you’re describing.
Sounds more like something a county might get away with.
Understand though, county and city have they’re own precincts and are usually below state requirements.

anyway, that’s my 2c worth :wink:

Where are you seeing this type of rail? Is it on the medians of a divided highway? They’ve just started using this light rail here in Austin. It’s not designed to physically prevent you from leaving the road like Metal Beam Guard Fence (used at bridges and steep drop-offs) does; the width of the median is adequate for that. It’s just supposed to prevent you from crossing the median either accidently (if you fell asleep it will wake you) or on purpose (people who illegally cut across for a u-turn). I’ve just dug around the TxDOT site looking for a cite but can’t find one. Lemme ask around and get back to you.

Here’s a brief (not horribly informative) TxDOT News Release about the installation of the median barrier.

And a second and a third.

Here is a Google cache (original seems to be gone) of an article about the apparent superiority of weak post over strong post systems. While it specifically addresses the “W” barrier, it mentions cable barriers, as well. I am guessing that weak post barriers and cable barriers do a better job of slowing and stopping a vehicle without inflicting as much “second crash” trauma to passengers, while a strong post barrier acts as a wall into which the vehicle smashes.

Improvements to the weak post guardrail

OK, more than you ever wanted to know. Search for “cavble median barrier” and you’ll get a whole slew of articles. Like this one about a study in Washington state.

So evidently they’re better at keeping cars from bouncing back onto the highway and crashing onto another car than traditional single slope safety rail or MBGF, which is interesting to know. And, yes, they do look flimsy, but keep in mind, they barriers aren’t designed to take a head on blow, generally cars and trucks hit the barrier at an glancing angle.

That should obviously be “cable median barrier”.

Well that’s just amazin. I assumed that the W barriers “had to be stronger” and therefore “safer”. Interesting to read the details and see why, in some cases, weaker is better.

Thanks! Another mystery solved.