# Guide Rail or Guard Rail? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [June 5, 2019, 1:53pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073 "2019-06-05T13:53:44Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [June 5, 2019, 1:53pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/1 "2019-06-05T13:53:44Z")
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. [This is the sign](https://imgur.com/XawppVG)posted along the road, warning drivers not to plummet. What? “Guide Rails”? I would call them Guard Rails. Amiright?😕 ---
**Author:** ![llcoolbj77](https://avatars.discourse-cdn.com/v4/letter/l/eb9ed0/32.png) [@llcoolbj77](https://boards.straightdope.com/u/llcoolbj77)\ **Post date:** [June 5, 2019, 1:55pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/2 "2019-06-05T13:55:20Z")
guard rails for sure. ---
**Author:** ![somepumpkin](https://avatars.discourse-cdn.com/v4/letter/s/7feea3/32.png) [@somepumpkin](https://boards.straightdope.com/u/somepumpkin)\ **Post date:** [June 5, 2019, 2:06pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/3 "2019-06-05T14:06:19Z")
Guard rail. Unless there’s ~ 2 feet of snow in the area. Then one might use them as “guide” rails. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [June 5, 2019, 2:06pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/4 "2019-06-05T14:06:48Z")
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’. ---
**Author:** ![TRC4941](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/trc4941/32/6792_2.png) [@TRC4941](https://boards.straightdope.com/u/TRC4941)\ **Post date:** [June 5, 2019, 2:07pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/5 "2019-06-05T14:07:08Z")
Guard rails for me. Guide rails sound like something that would guide you over the edge! ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 5, 2019, 2:07pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/6 "2019-06-05T14:07:28Z")
There wasn’t a guide rail or guard rail. How do you know which the sign referred to? Guide rails show you the way. Guard rails protect you. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [June 5, 2019, 2:12pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/7 "2019-06-05T14:12:28Z")
> [@TriPolar](#): > > There wasn’t a guide rail or guard rail. How do you know which the sign referred to? 😃 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. ---
**Author:** ![Alpha\_Twit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alpha_twit/32/265_2.png) [@Alpha\_Twit](https://boards.straightdope.com/u/Alpha_Twit)\ **Post date:** [June 5, 2019, 2:34pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/8 "2019-06-05T14:34:13Z")
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. ---
**Author:** ![robardin](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@robardin](https://boards.straightdope.com/u/robardin)\ **Post date:** [June 5, 2019, 2:53pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/9 "2019-06-05T14:53:30Z")
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. ---
**Author:** ![Tired\_and\_Cranky](https://avatars.discourse-cdn.com/v4/letter/t/a87d85/32.png) [@Tired\_and\_Cranky](https://boards.straightdope.com/u/Tired_and_Cranky)\ **Post date:** [June 5, 2019, 2:57pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/10 "2019-06-05T14:57:33Z")
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](http://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.” [Guardrail Basics - FHWA Review of ET-Plus | Federal Highway Administration](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. ---
**Author:** ![robardin](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@robardin](https://boards.straightdope.com/u/robardin)\ **Post date:** [June 5, 2019, 2:59pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/11 "2019-06-05T14:59:39Z")
Doh, I realized I gave an example of eastbound/westbounds lanes of I-95… Which runs north-south… And missed the edit window to fix it. Please let it slide 🙂 ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [June 5, 2019, 2:59pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/12 "2019-06-05T14:59:49Z")
> [@kayaker](#): > > 😃 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. OK, you probably got it right 🙂 Maybe it’s a thing in your locale. Maybe they ordered a ‘No Guard Rail’ sign and got 'No Guide Rail". At least each of those words is spelled correctly. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [June 5, 2019, 3:06pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/13 "2019-06-05T15:06:17Z")
> [@robardin](#): > > 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. 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. ---
**Author:** ![Omar\_Little](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/omar_little/32/269_2.png) [@Omar\_Little](https://boards.straightdope.com/u/Omar_Little)\ **Post date:** [June 5, 2019, 3:16pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/14 "2019-06-05T15:16:16Z")
Per Wikipedia: > **[Guide rail](https://en.wikipedia.org/wiki/Guide_rail)** > > A guide rail is a device or mechanism to direct products, vehicles or other objects through a channel, conveyor, roadway or rail system. > Several types of guide rails exist and may be associated with: > Most factories use guide rails convey products and component parts along an assembly line. This conveyor system propels products of various sizes, shapes, and dimensions through the factory over the course of their assembly. > Accessory to a power tool, such as a straight, swivel or angle jig for ... > [@](#): > > **Roadway guide rail** > > A guide rail is a system designed to guide vehicles back to the roadway and away from potentially hazardous situations. _ **There is no legal distinction between a guide rail and a guard rail** _. Several types of roadway guide rail exist; all are engineered to guide vehicular traffic on roads or bridges. Such systems include W-beam, box beam, cable, and concrete barrier. Each system is intended to guide vehicles back onto the road as opposed to guard them from going off the road into potential danger. ---
**Author:** ![Patch](https://avatars.discourse-cdn.com/v4/letter/p/a183cd/32.png) [@Patch](https://boards.straightdope.com/u/Patch)\ **Post date:** [June 5, 2019, 8:09pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/15 "2019-06-05T20:09:56Z")
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. ---
**Author:** ![Patch](https://avatars.discourse-cdn.com/v4/letter/p/a183cd/32.png) [@Patch](https://boards.straightdope.com/u/Patch)\ **Post date:** [June 5, 2019, 8:20pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/16 "2019-06-05T20:20:38Z")
> [@Joey\_P](#): > > 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. 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. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [June 5, 2019, 10:45pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/17 "2019-06-05T22:45:32Z")
> [@Tired\_and\_Cranky](#): > > . . . Apparently, the FHWA thinks it should be one word but even they aren’t consistent about it. If you’re submitting a grant for federal funds, call them guardrails. They like that. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [June 5, 2019, 11:00pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/18 "2019-06-05T23:00:50Z")
> [@robardin](#): > > Doh, I realized I gave an example of eastbound/westbounds lanes of I-95… Which runs north-south… And missed the edit window to fix it. Please let it slide 🙂 It’s true that I-95 is technically a north-south road from beginning to end, but it runs pretty much due east-west through all of Connecticut. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [June 5, 2019, 11:42pm UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/19 "2019-06-05T23:42:26Z")
> [@kayaker](#): > > 😃 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. Okay, now let’s determine what a “PTO device” is. [This list](https://acronyms.thefreedictionary.com/PTO) isn’t helping… ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [June 6, 2019, 11:06am UTC](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073/20 "2019-06-06T11:06:14Z")
> [@Patch](#): > > 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. Thanks for the insider info! > [@Darren\_Garrison](#): > > Okay, now let’s determine what a “PTO device” is. [This list](https://acronyms.thefreedictionary.com/PTO) isn’t helping… Sorry. Power Take Off. It’s what they call implements driven by the engine on a tractor. I think that’s how they were pulling out the posts. [Next page](https://boards.straightdope.com/t/guide-rail-or-guard-rail/835073.md?page=2)