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[XamotCGC]

Can the existing shoulders on a two lane highway be converted to or widen enough for use as another driving lane?

[Rothman]

Yes.

[Bruce]

Don't see why it would be any different from a parking lane that is converted for thru traffic during peak hours (tons of those in cities).

A slightly different case in Kenmore, WA, where this street has a marked shoulder/parking lane that opens as a long queue lane for a right turn during afternoon peak.

[Scott5114]

I think in some states, a shoulder may not be built to the same thickness or durability level as the travel lanes, due to the expectation of lower wear. I seem to recall there being a discussion on here of afreeway work zone where the travel lanes were realigned outward so that the right lane partially rode on the shoulder, and trucks were directed to use the left lane because, unlike the mainlines, the shoulder wasn't built to withstand heavy truck traffic.

[Bruce]

I think in some states, a shoulder may not be built to the same thickness or durability level as the travel lanes, due to the expectation of lower wear. I seem to recall there being a discussion on here of afreeway work zone where the travel lanes were realigned outward so that the right lane partially rode on the shoulder, and trucks were directed to use the left lane because, unlike the mainlines, the shoulder wasn't built to withstand heavy truck traffic.

We had a similar situation in the Seattle area when adding bus-only shoulders. They had to be reconstructed a bit to move weaker drainage equipment and junction boxes that wouldn't be able to handle the weight.

[Rothman]

The OP asked about converting shoulders to traveling lanes.  I don't see how this doesn't happen with any project that adds an additional lane.

[cbeach40]

Can the existing shoulders on a two lane highway be converted to or widen enough for use as another driving lane?

Yes, though the road bed and the surface of the shoulder would need to be reconstructed to handle highway traffic. But could be done within the same physical space.

Doing so however will of course remove the shoulder, which can have negative consequences regarding things like roadside safety (removes the margin of safety a shoulder provides), guiderail or barrier placement, space for ped/bikes, room for oversize vehicles (like farm equipment), snow removal. Also through curves, especially on the outside of a superelevated (banked) curve, the reconstruction would be more substantial and may not be able to be done within the existing space.

[epzik8]

I-95 between Baltimore and Wilmington, the John F. Kennedy Memorial Highway, was two lanes in each direction upon opening in 1963. The shoulders of the Tydings Bridge over the Susquehanna River were made wide enough to be turned into a third lane in each direction, which eventually did happen along the entire highway.

[skluth]

I think most of us have driven on shoulders as temporary lane during highway construction somewhere. I remember some instances where signs directed trucks to stay in the left lane and only cars were allowed to drive on the shoulder, though this wasn't the usual. When I lived in Tidewater, I-264 just east of the I-64 interchange allowed rush hour traffic to drive on the shoulder east to at least Witch Duck (this was about 15 years ago).

[hbelkins]

Examples of shoulders being converted to temporary travel lanes I've seen in recent years include I-66 in the DC area of NoVA, I-70 west of Denver, and US 23 north of Ann Arbor.

The reason that the Brent Spence Bridge is considered functionally obsolete is that it was originally built for three lanes with shoulders, but because of increasing traffic, was restriped to be four lanes with no shoulders.

I think in some states, a shoulder may not be built to the same thickness or durability level as the travel lanes, due to the expectation of lower wear. I seem to recall there being a discussion on here of afreeway work zone where the travel lanes were realigned outward so that the right lane partially rode on the shoulder, and trucks were directed to use the left lane because, unlike the mainlines, the shoulder wasn't built to withstand heavy truck traffic.

You are correct. In areas where the shoulders are pressed into service as travel lanes during long-term construction projects, it's common to see "Trucks Use Left Lane" signage.

[Dirt Roads]

I think in some states, a shoulder may not be built to the same thickness or durability level as the travel lanes, due to the expectation of lower wear. I seem to recall there being a discussion on here of afreeway work zone where the travel lanes were realigned outward so that the right lane partially rode on the shoulder, and trucks were directed to use the left lane because, unlike the mainlines, the shoulder wasn't built to withstand heavy truck traffic.

You are correct. In areas where the shoulders are pressed into service as travel lanes during long-term construction projects, it's common to see "Trucks Use Left Lane" signage.

There have also been some freeways where the third lane was added in the median, and the permanent lane did not have sufficient subgrade to handle truck traffic.  These are often in areas that also use "No Trucks Left Lane" signage for the far left lane, which serves both to allow cars an additional passing lane without trucks.  Once upon a time, I could have remembered where these were most common, but I'd better not guess.

[Big John]

In Georgia there are frequent signs saying trucks with over 6 wheels are prohibited on left lanes on freeways that are 6 lanes or more.  I believe that it is meant for traffic control.

[hbelkins]

There have also been some freeways where the third lane was added in the median, and the permanent lane did not have sufficient subgrade to handle truck traffic.  These are often in areas that also use "No Trucks Left Lane" signage for the far left lane, which serves both to allow cars an additional passing lane without trucks.  Once upon a time, I could have remembered where these were most common, but I'd better not guess.

Both Kentucky and West Virginia typically prohibit trucks in the left lane of three-lane routes, although the verbiage on the signs is different. Kentucky is permissive -- "Trucks Use Right 2 Lanes" -- while West Virginia gets the point across better -- "Left Lane No Trucks." Of course Kentucky has more full three-lane interstates while West Virginia's are more common only for truck climbing lanes. In both cases, it's more to prohibit trucks stacked three-deep micropassing rather than issues with the road's ability to support the weight of the vehicles.

[cbeach40]

There have also been some freeways where the third lane was added in the median, and the permanent lane did not have sufficient subgrade to handle truck traffic.  These are often in areas that also use "No Trucks Left Lane" signage for the far left lane, which serves both to allow cars an additional passing lane without trucks.  Once upon a time, I could have remembered where these were most common, but I'd better not guess.

Both Kentucky and West Virginia typically prohibit trucks in the left lane of three-lane routes, although the verbiage on the signs is different. Kentucky is permissive -- "Trucks Use Right 2 Lanes" -- while West Virginia gets the point across better -- "Left Lane No Trucks." Of course Kentucky has more full three-lane interstates while West Virginia's are more common only for truck climbing lanes. In both cases, it's more to prohibit trucks stacked three-deep micropassing rather than issues with the road's ability to support the weight of the vehicles.

For Ontario, leftmost lane prohibitions on 6+ lane freeways are the same, strictly due to operation and traffic flow, not the road structure.
Signage is of course graphic indicating the prohibition.

[Dirt Roads]

There have also been some freeways where the third lane was added in the median, and the permanent lane did not have sufficient subgrade to handle truck traffic.  These are often in areas that also use "No Trucks Left Lane" signage for the far left lane, which serves both to allow cars an additional passing lane without trucks.  Once upon a time, I could have remembered where these were most common, but I'd better not guess.

In Georgia there are frequent signs saying trucks with over 6 wheels are prohibited on left lanes on freeways that are 6 lanes or more.  I believe that it is meant for traffic control.

Both Kentucky and West Virginia typically prohibit trucks in the left lane of three-lane routes, although the verbiage on the signs is different. Kentucky is permissive -- "Trucks Use Right 2 Lanes" -- while West Virginia gets the point across better -- "Left Lane No Trucks." Of course Kentucky has more full three-lane interstates while West Virginia's are more common only for truck climbing lanes. In both cases, it's more to prohibit trucks stacked three-deep micropassing rather than issues with the road's ability to support the weight of the vehicles.

During construction, you can usually tell whether the new lane is getting a full-depth subgrade or a partial-depth subgrade.  Unless you have access to the designs, that's the only way to be sure whether the "Left Lane No Trucks" sign is a road maintenance requirement versus a "don't let truckers block all the lanes" mentality.

[jeffandnicole]

Is the OP asking about converting shoulders to travel lanes during the construction project, or permanently converting the shoulders to a travel lane?

The latter is generally not permissible, especially regarding interstate highways. Non-interstate widenings often will convert shoulders to travel lanes where full shoulders aren't feasible.

On a temporary basis though during a project, it's ultra-common.

[triplemultiplex]

Lots of places allow traffic to use the shoulder lane during peak travel times.  It's a useful stop-gap measure where expanding the road more permanently is not in the cards financially or physically.  They have a bunch of shoulder lanes out in Hawaii.  Pretty sure they are also in use on the super 2 portion of US 6 out toward The Cape.  They run buses on the shoulder lanes around Chicago.

[DJStephens]

Is the OP asking about converting shoulders to travel lanes during the construction project, or permanently converting the shoulders to a travel lane? quote]

They did it in Massachusetts.  Route 128 (re-routed 95) around the W side of Boston allowed rush hour traffic to use the breakdown lane for decades on the six lane section between State route 9 and 95 in Dedham.  Believe it was also done on I-93 N of the lane drop between 128 and I-495.  Used to refer to the "lanes" as Salvucci lanes, after the infamous transportation secretary.