10 Foot Shoulders

[Mergingtraffic]

Why were 10 foot shoulders the standard on limited access highways?  You would think shoulders would hav been designed to be wider so people have room to move or fix things.

Also, how come there were no standards to include a full left hand shoulder?

[J N Winkler]

Full-width shoulders are typically not provided on the left-hand side because drivers are not supposed to use the left-hand shoulder for stopping.  The primary purpose of a left-hand shoulder is to allow errant vehicles some room to recover on a paved or stabilized surface.

10' is in excess (sometimes well in excess) of the width of most cars, trucks, and buses in regular production.  It is therefore adequate paved width for typical roadside recovery operations (towing, changing a flat tire, etc.) except in certain situations, such as shoulders immediately adjacent to walls, which may attract added shoulder width for this reason.  Wider shoulders can be provided in ordinary cut or fill as well, but because of the added expense, this tends to be limited to freeways with high AADT or high truck percentages.

A vehicle parked on the shoulder is a sitting target for errant vehicles, regardless of shoulder width, and this is one reason motorist assistance patrols are provided on freeways with high AADT.  Another is to encourage stranded drivers to leave the roadway environment ASAP.

[jjakucyk]

Shoulder and lane width standards for interstates have gotten pretty excessive as of late IMO.  I-75 between the Cincinnati Beltway (I-275) and I-675 in Dayton is being widened from 6 to 8 lanes total.  The thing is, what was 3 lanes each way with a paved right shoulder and a few feet of pavement on the left (totaling about 8 1/2 lanes in width) with a small grass median in the middle is now 12 full lanes wide with a concrete barrier down the middle.  That's 4 whole lanes out of the 12, a third of the pavement, that's not meant to be driven on.  Or to put it another way, a 33% increase in capacity required a 41% increase in pavement, assuming the lanes and shoulders remained the same width.  Of course they didn't.  12 foot travel lanes are now 14 feet, and both shoulders look to be at least 12 feet wide.  That makes the 33% capacity increase require 63% more pavement.  They could've made this a 10 lane highway keeping the old geometry.  I just find that to be hugely wasteful. 

Now there are other instances, such as the late 1950s era portions of I-75 closer in to Cincinnati that have some serious geometry issues.  There's some hills with blind crests, short merges, 12 foot through lanes, 8 foot right shoulders, and no left shoulder to speak of (you have basically two feet from the left lane line to the concrete jersey barrier).  It would be preferable that there isn't a barrier next to the left lane, whether the shoulder is paved or not.  Still, I believe current Interstate design standards require a full left shoulder when there are three or more through lanes each way.  So to rebuild this road with the same capacity but to current standards would require widening it by 35%.  Of course that's not going to happen, a lane must be added so its LoS will stay at "D", and this being a very densely built urban corridor.  Ouch. 

[vdeane]

The Thruway between exits 39 and 40 now has full-width left shoulders.  I'm not sure if it's a new Thruway standard or if it's so they could shift the traffic over to one side without closing any lanes.

[Mergingtraffic]

that what I am saying there are 12 foot travel lanes for whatever reason but 10 foot wide shoulders.  Why not make shoulders 12 feet as well?  10 feet for maneuvering (such as changing a tire) and a vehicle is not much room.  That is if the vehicle is all the way over to the edge of the pavement.  If you have a guardrail on one side, you need room to get out.  Add to the fact that cars traveling past at 60mph

Although in CT, when interstates are widened they now have 12 foot wide inside and outside shoulders. 

[jjakucyk]

That pavement isn't free doofy.  Shoulders are a pretty expensive piece of infrastructure considering they're rarely used for much.  I think it'd be more prudent to expand the usable part of the shoulder with gravel and proper grading than yet more pavement. 

[3467]

Most of the original state roads in Illinois had 9 foot travel lanes. 10 feet is very good for shoulders especially paved .
Iowa has a good standard for its 2 lane primary(CIN) system 24 feet of travel lanes,10 foot paved or graded shoulders passing lanes and 65 mph geometrics.
Such width also allows future options like a 4 lane undivided or a continuos 3 lane with not a lot of effort for lower volume rural roads
St Louis is cutting its I 270 travel lanes to 11 feet so 10 feet is great for shoulders.I wish every raod had them

[Mergingtraffic]

That pavement isn't free doofy.  Shoulders are a pretty expensive piece of infrastructure considering they're rarely used for much.  I think it'd be more prudent to expand the usable part of the shoulder with gravel and proper grading than yet more pavement. 

I've noticed....in my state, when they mill and repave the road, they only do the lanes and leave ths shoulders intact.

[Alps]

Our engineering and operational understanding gets better as time goes on. 12 feet are now the desirable standard to achieve for a right shoulder. If we knew 50 years ago what we know now, the Interstate system would have been designed to much higher standards.

[Sykotyk]

Exactly. Same reason cloverleaf interchanges are considered substandard today but were the primary setup for freeway-to-freeway movement before.

[1995hoo]

That pavement isn't free doofy.  Shoulders are a pretty expensive piece of infrastructure considering they're rarely used for much.  I think it'd be more prudent to expand the usable part of the shoulder with gravel and proper grading than yet more pavement. 

On the other hand, here in the DC area sometimes it seems like the shoulder is the passing lane, especially near the Pentagon during the morning rush hour. 

[Mergingtraffic]

Our engineering and operational understanding gets better as time goes on. 12 feet are now the desirable standard to achieve for a right shoulder. If we knew 50 years ago what we know now, the Interstate system would have been designed to much higher standards.

That is true, most projects in my state have 12 foot right and inside shoulders.  Kinda surpised at some of the negativity towards this topic.