Thrie Beam Guardrail

[Brandon]

I have noticed throughout the years, that thrie beam guardrail seems to be fairly rare outside of Michigan.  MDOT tends to use a lot of it while most of the DOTs tend to use it only prior to bridges to attach W-rail to a concrete barrier.  Prior to installing thrie beam, MDOT used to use two overlapping W-rails.

Is there a reason for this?

[agentsteel53]

where did the spelling "thrie" come from?  I thought first it was a proper noun, but it looks to just be a bastardization of the word "three", whose origin is visually obvious.

[Big John]

Thrie beam is usually used in transitions from the less stiff W-beam guard rail to the solid concrete barrier.   Being it is stiffer than the W-beam to make a better transitionbetween those 2 barriers to make a crash less severe.  Cost is a factor in why most states use the W-beam instead of thrie beam except in transitional areas.

[cbeach40]

According to one of the first results I found, the deflection of Thriebeam is about 0.6 m. MTO uses 0.9 m for traditional W-rail, and 0.3 m with a channel. So it's kind of a thin margin that Thriebeam falls in between a standard rail and a fitting it with a channel.

Segment of rail both with and without channel:
http://goo.gl/maps/UusjR

The other advantage of using Thriebeam is the increased surface area, which helps in areas with significant heavy vehicle volumes.

I can't speak for other jurisdictions, for retrofits, MTO will tend to go with the channelized rail. For new build, MTO handles it in their typical overkill fashion:
http://goo.gl/maps/YdQly

[Brandon]

For a contrast, here's a typical MDOT installation:

https://maps.google.com/maps?hl=en&ll=42.305213,-84.994601&spn=0.002305,0.005284&t=h&z=18&layer=c&cbll=42.305053,-84.995655&panoid=TOlCgfINOAg8NKV1RXyR1g&cbp=12,192.28,,0,10.58

[briantroutman]

Everything you ever wanted to know about thrie beam guardrail is in this video from the FHWA:(https://archive.org/details/gov.dot.fhwa.ttp.vh-2b)

Thrie is apparently just an archaic (Old Saxon) version of "three" , but why it's used in this specific case is beyond me. If you search "thrie"  in Google most of the first page results are related to the guardrail.

[mass_citizen]

thrie beam is the standard for all median guardrail (where concrete is not used) in Massachusetts

[Alps]

NJDOT does not use Thrie in any application. I believe NYSDOT and/or NYSTA are fully accepting, on the other hand (though box beam prevails in most occurrences).

[Tom958]

Everything you ever wanted to know about thrie beam guardrail is in this video from the FHWA:(https://archive.org/details/gov.dot.fhwa.ttp.vh-2b)

Wow, I'm converted.

Has anyone investigated the feasibility of retrofitting thrie beams to existing W beam installations? Perhaps with a steel sleeve that fits snugly over the existing shorter posts? I'm thinking there are several hundred miles of W beam median barrier in Georgia alone that really should be thrie beam instead if it wasn't cripplingly expensive to retrofit.

[jeffandnicole]

NJDOT does not use Thrie in any application.

Sure they do.  Where I-295 was reconstructed from Exits 45 to 57 several years ago, Thrie was used the entire length within the median.  http://goo.gl/maps/9kZzq  You can clearly see the different between the W (used on the far shoulder) & the Thrie.

Another example on NJ 29 between 195 & the Trenton Tunnel, when guiderail was either added or upgraded from existing W: http://goo.gl/maps/YkbXS

In their engineering documents online, the use of Thrie guiderail is mentioned here (Section 8.4.1 Part C): http://www.state.nj.us/transportation/eng/documents/RDM/sec8.shtm#warrantsmedbar

[Tom958]

I just saw a crew installing a new non-modified thrie beam guardrail on I-85 near Atlanta. I'm pist. Shouldn't I be?

[cpzilliacus]

I have noticed throughout the years, that thrie beam guardrail seems to be fairly rare outside of Michigan.  MDOT tends to use a lot of it while most of the DOTs tend to use it only prior to bridges to attach W-rail to a concrete barrier.  Prior to installing thrie beam, MDOT used to use two overlapping W-rails.

Is there a reason for this?

Maryland uses them mostly for those transitions from "W" rails to Jersey-style concrete barriers.

Only place I know of with thrie beam guardrail is on I-270 Southbound in Rockville, Montgomery County.

[cl94]

It's rarely used in New York except in a few cases near bridge piers, impact attenuators and other locations. Box beam guide rail serves a nearly-identical purpose and is much more common, likely because less metal is required to achieve a similar moment of inertia.