"Congestion-Proof" Freeways

[webny99]

Some discussion in another thread got me thinking about cases where a new lane opens up on a freeway and there are no new entrances for a considerable distance (or where any new entrances also contribute through lanes, providing an "extra" lane).

Most often, this would be where there are two lanes in one direction and it expands to three lanes. Using that as an example, the section with two lanes restricts the amount of traffic that can reach the 3 lane section. So, even if the two lanes are at full capacity, it's still not enough to fill the full three lanes. This effectively guarantees that there will not be congestion on that 3 lane section. Obviously, there can be an incident that causes a backup, or downstream congestion, but under normal circumstances, congestion will not occur there because only 2 cars can reach that section at once and there's 3 lanes to use.

The example that comes to mind in my area is this section of I-490 where a third lane opens south of NY 153 and the on ramp from the next pair of exits is almost 2 miles away. So both sides of this segment often get congested but you're pretty much guaranteed to keep moving on this 2 mile segment.

I'm curious what other examples exist and what is the longest example we can find of a built-in congestion-proof freeway segment (not counting ramp meters or anything related to a specific incident or construction project).

[Max Rockatansky]

I don't recall ever running into a traffic jam on the Glendale Freeway segment of CA 2.  The traffic always seemed to be on the south end of the freeway as CA 2 transitioned into Glendale Boulevard.  I think the phenomenon I used to see was that the Glendale Freeway simply wasn't utilized by many despite being close to downtown Los Angeles.

[Dirt Roads]

We just had a discussion about the short section of I-85 [westbound] just west of Hillsborough that widens to three lanes in approach to the merge with I-40 to become "The Spine of North Carolina".  This section opened in the early 1990s as part of widening The Spine to eight lanes.  The [eastbound] lanes of I-85 needed to be 3 lanes to improve truck flow at The Split headed up the short distance to the top of Occoneechee Mountain, and I highly suspect that the [westbound] lanes were widened in anticipation that the entire stretch of I-85 between The Split and Durham would need to widened soonafter.  Still ain't started, but they did survey for that widening project about 7 or 8 years ago.

[RobbieL2415]

Are you sure the intent by the added lane there is as you say it is?
It does appear to be provisioned for an extension with a few hundred feet of wider shoulder.

[Dirt Roads]

Are you sure the intent by the added lane there is as you say it is?
It does appear to be provisioned for an extension with a few hundred feet of wider shoulder.

The [eastbound] lanes are fairly steep and need a truck climbing lane after The Split.  Without it, traffic would back up significantly in the left two lanes before The Split.  But the current arrangement causes problems as well.  Truckers that get into either of the left two lanes before The Split cause I-85 traffic to pass on the right side (interfering with I-40 traffic).  Truckers that stay in the second lane from the right hit the upgrade before The Split and slow down the "fast lane" heading to I-40.  But even with two miles of advance notice with overhead diagrammatics, everyday you see traffic headed for I-40 get caught in the two left lanes and slash across the lanes and split the gore (the one I saw today had to stop in the gore and wait to pull into the fast lane later).

[webny99]

We just had a discussion about the short section of I-85 [westbound] just west of Hillsborough that widens to three lanes in approach to the merge with I-40 to become "The Spine of North Carolina".  This section opened in the early 1990s as part of widening The Spine to eight lanes.  The [eastbound] lanes of I-85 needed to be 3 lanes to improve truck flow at The Split headed up the short distance to the top of Occoneechee Mountain, and I highly suspect that the [westbound] lanes were widened in anticipation that the entire stretch of I-85 between The Split and Durham would need to widened soonafter.  Still ain't started, but they did survey for that widening project about 7 or 8 years ago.

Yep, that was exactly the discussion that inspired this thread, along with the example on I-490 that I mentioned in the OP.

Are you sure the intent by the added lane there is as you say it is?
It does appear to be provisioned for an extension with a few hundred feet of wider shoulder.

The [eastbound] lanes are fairly steep and need a truck climbing lane after The Split.  Without it, traffic would back up significantly in the left two lanes before The Split.  But the current arrangement causes problems as well.  Truckers that get into either of the left two lanes before The Split cause I-85 traffic to pass on the right side (interfering with I-40 traffic).  Truckers that stay in the second lane from the right hit the upgrade before The Split and slow down the "fast lane" heading to I-40.  But even with two miles of advance notice with overhead diagrammatics, everyday you see traffic headed for I-40 get caught in the two left lanes and slash across the lanes and split the gore (the one I saw today had to stop in the gore and wait to pull into the fast lane later).

That seems like a no-win situation for trucks trying to keep right. Isn't I-40 the busier movement here? In that case it would make more sense to have three lanes going to I-40 and two to I-85. The ideal setup would probably be to add a fifth lane from Exit 161 and have three lanes for both I-40 and I-85 (at least when the I-40 widening is complete).

[Dirt Roads]

There's also one in my old backyard, but it doesn't always seem congestion proof.  I-64 westbound currently widens from two lanes to three lanes just west of Rock Stepp Road (near MM 41) and runs great until the lane drop at Exit 39 for Teays Valley.  Since a significant portion of the westbound traffic is heading for US-35 or the Teays Valley exit, this has all the making of a congestion-proof freeway.  But alas, there are those moments where Exit 39 backs up onto the right lane exit only (sheer volume), or on occasion, I-64 chokes down from three lanes to two lanes heading westward towards Hurricane -and- Huntington.

It's going to take a while, but the four-lane section of I-64 between MM 41 and MM 45 is currently being widened, including the new twin-bridge replacement over the Kanawha River.

[Alex4897]

I-95 southbound picks up a 4th lane coming out of Philadelphia just after the Schuykill River. The right lane ducks into a CD ramp for PA 291 and the Philly Airport not long after, but it's about 1.75 miles before traffic from the next on-ramp meets the main lanes and loses the lane it came with.

We just had a discussion about the short section of I-85 [westbound] just west of Hillsborough that widens to three lanes in approach to the merge with I-40 to become "The Spine of North Carolina".  This section opened in the early 1990s as part of widening The Spine to eight lanes.  The [eastbound] lanes of I-85 needed to be 3 lanes to improve truck flow at The Split headed up the short distance to the top of Occoneechee Mountain, and I highly suspect that the [westbound] lanes were widened in anticipation that the entire stretch of I-85 between The Split and Durham would need to widened soonafter.  Still ain't started, but they did survey for that widening project about 7 or 8 years ago.

The north/eastbound approach into Durham's a good example too, it's about 2.5 miles between the third lane opening up and the onramps from Cole Mile Road and US 15 / 501. The whole of I-85 through Durham seems to behave this way in either direction, at least in my experience.