Earth Berm for Traffic Control? 1

[Riversidean]

Currently I have been asked to look into possibly using a earth constructed berm instead of a traffic barrier on the oustide edge of a road which is at the hinge to a fairly steep slope. Researching the subject on my own I am concerned about the berm merely becoming a truck ramp for the TL-5 (Test Level 5) tractor-van trailers (based on NCHRP 350) going on the turn and the amount of space it may to build such a berm.

Does anyone know of any design standards for earthen berms used as traffic barriers? I have seen discussion of earthen berms used in mining operation manuals, but other then that everything seems to be made of casted concrete for traffic barrier devices. Or any other ideas?


Is there any temporary TL-5 barrier in existence?

Thanks,
Riversidean

 

[cvg]

I'm not a traffic engineer. But I know a stable earth berm will have at least 2H:1V and probably 3H:1V side slope. If it needs to be mowed than shoot for at least 3H:1V or flatter. this is an ideal launch angle for a moving vehicle. That's why most barriers and curbs are vertical concrete for any speeds over about 15 mph.

 

[civilman72]

As far as I know, acceptable roadside barriers are listed in the AASHTO Roadside Design Guide (RDG) and there is no mention of an earthen berm roadside barrier.

Minimum "recoverable" slope for a vehicle is 4:1, anything steeper and it's anticipated the vehicle may roll. A "recoverable" slope actually means a slope that you can control your vehicle on until it (theoretically) goes to the bottom of the fill slope. I believe on 6:1 slopes or flatter it's anticipated that the driver can potentially manuever the vehicle back onto the road (although this is also a safety concern).

Not only would you need a flat slope, but I would imagine the berm would have to be fairly high to dissipate the vehicle momentum and stop it from going over the other side and down the steep slope. This massive structure will more than likely not fit in the confined area between the edge of road and steep slope. In summary, it does not seem like a feasible application.

If there are severe and consistent vehicle accidents caused by this steep slope, then the installation of a barrier is legitimate. Otherwise, I would also highly recommend that you think twice before installing any kind of roadside barrier. The perceived notion that a portion of a roadside is "dangerous" can lead you to install a potentially more dangerous roadside barrier. You can read more about this is the RDG.

 

[Hoagie]

I've seen this in mining operations--where you have a minimum height of berm that relates to tire height (for truck driver safety). I know MSHA has criteria. I'd check out the Mine Safety and Health Administration website.

 

[BigH]

Hoagie hit the homer . . . here in Indonesia, it is a requirement that all mine roads have a berm. It is related to the maximum tyre size - must be more than 1/2 the diameter of the tyre (from memory). They are usually not constructed at 3H:1V slopes - but more like 1/2H:1V (it is a small height).

 

[mathmday]

Riversidean,

I just got done submitting guardrail plans for a USFS road where our design speed is 20 MPH but a very high ADT. I looked into berms as a permanent barrier but in only one location did we find that it was feasable due to space constraints. The only specifications / guidelines that I even found mention to this was in the USFS specifications.

Needless to say through my research I found that the only barriers that an engineer can really hang his hat on were those meeting NCHRP 350 requirements when the application is on Public ROW.

If this is a Private sector application, then the guidelines that Hoagie and BigH have lined out seem to be the ticket!

Hope you go though less headaches than I did! Cheers :O)