A road I travel on daily is undergoing construction (destruction?). They are removing all of the metal rails that stop cars from plummeting off the road. I assume these rails will eventually be replaced by new and improved rails.
I don’t think I’ve ever heard of them called anything other than Guard Rails and googling the two phrases seems to agree with this.
My guess is that either “guide rails” is their actual, real DOT name or more likely the sign maker calls them that so that’s how they wrote it out. Similar to someone calling the cables that go from the ground up to a tall pole or tower ‘guide wires’ when they’re actually ‘guy wires’.
The day before I saw the first sign, I saw them ripping out the guard rails. It’s quite the undertaking, BTW. They were cutting the horizontal piece into uniform lengths (wow, the sparks!) and then using a cool PTO device to pull out the vertical members.
I have heard the term ‘guide rail’ but I agree, ‘guard rail’ is much more common.
Before he retired, my dad worked on the Kansas state highway crew. Every year, usually in late autumn, the crew would spend a couple of weeks repairing and upgrading various sections of rail that needed some attention. I remember his telling me that ‘guide rail’ is the proper term used on the US Interstate system. Some state highway systems have adopted the term for official purposes to various degrees. Everyone just called them ‘guard rails’ for almost all cases except for official documents.
A “guide rail” is designed to keep something on a path (where there is a focus/narrow goal for what “staying on the path” means), while a “guard rail” is to prevent something from leaving the path (where there is a wide latitude for what “staying on the path” means, but a specific outcome to be avoided if something were to leave the path).
So, a “guide rail” is like a hand rail meant to help guide you in the dark to stay on a footpath (typically one with a steep drop or other hazard on at least one side), or a rail meant to keep a vehicle traveling in a grooved path. Or for cutting machinery, to ensure a straight cut. Leaving the fixed path could be a very bad outcome in pretty much all cases, so the “guide rail” ensures you stay on it.
You’re supposed to be able to make contact with a guide rail periodically, without harm.
But a “guard rail” is like a rail along a vehicular road with parallel traffic traveling in opposite directions, to guard against a vehicle crossing over into oncoming traffic. So I can freely move between any of the 2-4 lanes on the eastbound side of highway I-95 (assuming traffic allows it), but a “guard rail” is there to prevent me from going into the 2-4 westbound lanes of I-95 (which would never be safe to do).
If you touch a guard rail it’s the very last line of defense, you are already in trouble.
Of course, the similarity of the sounds of the words and the fact that they’re both called - and are - rails will mean some people will conflate them. Especially since some people may be accustomed to using the “guard rail” in the center of such a road to help stay in their lane at night or in poor visibility weather.
I’ve never heard of a “guide rail” before but Alpha Twit’s post got me curious.
I did a google search on the Federal Highway Administration’s website, fhwa.dot.gov and got the following surprising result:
“guide rail” = about 296 results
“guard rail” = about 317 results
“guardrail” (no space) = about 3,670 results, including the most authoritative source on “Guardrail basics.” https://www.fhwa.dot.gov/guardrailsafety/guardrailbasics.cfm
Apparently, the FHWA thinks it should be one word but even they aren’t consistent about it.
Along those lines, the guard rail, while designed to make sure you don’t end up in oncoming traffic is also designed to absorb as much of the impact as possible (by guiding your car to a stop) instead of ricocheting you back into traffic. If a driver is inattentive enough to end up hitting the rail, you don’t want them bouncing back onto the road, over correcting and having things go from bad to worse, quickly.
I’ve seen a lot of highways switch from rails to cables for this reason. They catch the car rather than allowing the car to bounce off it or ride up and over it.
Civil engineer here. I have never seen the term guide rail used before. Looking through the Big Book of Stuff We Can Put on Signs, also known as the Manual on Uniform Traffic Control Devices, the phrase ‘guide rail’ does not appear. I have no idea why they’re using the term guide rail. The MUTCD is put out by the Federal Highway Administration, and we’re not supposed to deviate from it, so that does not appear to be an allowable sign. Maybe it’s something old and still in their inventory, or the sign maker can’t hear very well.
The metal stuff with two humps is metal beam guard rail, or w-beam guard rail. If the splices are between the posts, a more recent configuration, it’s the Midwest guard rail system, or MGS. The three hump stuff is thrie beam barrier.
Guard rail isn’t meant to bring a car to a stop, and there’s nothing in the crash test criteria for guard rail to keep the car from coming off the system and back into traffic. We’d prefer it if the car did not, but beyond a criteria for an exit angle a vehicle is free to leave the rail and head off in another direction. Ideally, at a fairly shallow angle so it won’t re-enter traffic. End terminals are designed to stop a car, but the main system, if you hit it, you can expect to come off of it.
Vehicles striking cable barrier are capable of flattening the system out and going over the top, or sometimes slipping underneath the stuff, particularly if the system is on a slope.