Inside Lanes Merging

[jdbx]

In situations where one multi-lane road or ramp joins another, which states allow the center lanes to merge together while retaining the outside lanes?

Here's an example I found while browsing Street View for another thread. I think I've seen a similar situation in Ohio, but it strikes me as potentially unsafe, and I'm pretty sure that type of striping is not allowed here in New York.

There are a few places where this happens here in the SF Bay Area, often enough that I don't even consider it all that unusual...

The first one to come to mind, which is also fairly unpleasant to navigate at most times is where westbound CA-24 traffic has to merge with westbound I-580 traffic, in an area locally known as the MacArthur Maze.

https://www.google.com/maps/@37.8263458,-122.2762389,3a,75y,288.48h,84.63t/data=!3m7!1e1!3m5!1si7wS97c2f6hcIbskopMFaQ!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3Di7wS97c2f6hcIbskopMFaQ%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D355.29285%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192

There is another one not far from where I live where the I-680 North merges with I-80 East:

https://www.google.com/maps/@38.2189487,-122.1341968,3a,75y,61.73h,78.16t/data=!3m7!1e1!3m5!1sXqB9NOiFDUlRMLzOH6oPyA!2e0!6s%2F%2Fgeo2.ggpht.com%2Fcbk%3Fpanoid%3DXqB9NOiFDUlRMLzOH6oPyA%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D158.89418%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192

I am sure there are several others around here.

[webny99]

I think we need a poll on whether this should be banned or not. Overall, I still think so, but this thread has been enlightening as to how/why it can be useful in certain contexts.

[ran4sh]

I think it should be banned, in favor of either the left or right lane merging.

[interstatefan990]

Another NY example: https://goo.gl/maps/tDchZpL9QMRkD7Ns5

Personally, I think it should be banned. Much safer to do an added lane for the two center lanes and then right/left lane ends

[CtrlAltDel]

Personally, I think it should be banned. Much safer to do an added lane for the two center lanes and then right/left lane ends

Do we know this, though? It could be that they're fairly common where I'm from, but to me they don't seem more dangerous than anything else.

[interstatefan990]

Personally, I think it should be banned. Much safer to do an added lane for the two center lanes and then right/left lane ends

Do we know this, though? It could be that they're fairly common where I'm from, but to me they don't seem more dangerous than anything else.

Center-lane merging situations are usually difficult to post advance warning of since it seems to me they are often found on wide highways and drivers may miss a sign on the side of the road. When drivers reach the actual merging point and finally realize what's happening, they have to focus on three things at once: looking out for traffic merging from the through lane beside them, safely merging with the traffic from the merging lane, and keeping a safe distance from the traffic ahead of them. I'd err on the side of caution and say this is too much happening at once to be considered safe. However, I would make an exception for low-speed urban roads where there's less pressure, but only if there's a clearly visible merge sign providing advance warning.

[jamess]

I was almost in a collision near Montreal when driving there for the first time with a merge like this. Anyone know if it's more common up there?

[MarkF]

I've heard a reference to this type of merge as a "suicide squeeze".  There is one on the four-level in downtown L.A. at the northbound U.S. 101 merge from CA 110:
https://goo.gl/maps/e5x9zi2hb9SeTLdS6

and another at the East L.A Interchange on WB Interstate 10 where it connects with the ramp from SB Interstate 5:
https://goo.gl/maps/URo4KLSrw4KobCdj8

[jakeroot]

I really don't see why it's a big deal, besides being unusual. Merging occurs no matter which lane ends.

I think I've seen this somewhere in WA. But the actual last time I saw this, with certainty, was merging from southbound I-69 to I-465 northeast of Indianapolis.

[kphoger]

I'm fine with them on low-speed roads, but I'm a bit uncomfortable with them on high-speed roads.  With adequate signage, not such a huge deal, I suppose, but I'd still prefer a different design.

[CtrlAltDel]

Personally, I think it should be banned. Much safer to do an added lane for the two center lanes and then right/left lane ends

Do we know this, though? It could be that they're fairly common where I'm from, but to me they don't seem more dangerous than anything else.

Center-lane merging situations are usually difficult to post advance warning of since it seems to me they are often found on wide highways and drivers may miss a sign on the side of the road. When drivers reach the actual merging point and finally realize what's happening, they have to focus on three things at once: looking out for traffic merging from the through lane beside them, safely merging with the traffic from the merging lane, and keeping a safe distance from the traffic ahead of them. I'd err on the side of caution and say this is too much happening at once to be considered safe. However, I would make an exception for low-speed urban roads where there's less pressure, but only if there's a clearly visible merge sign providing advance warning.

All that makes sense, of course, but so does the idea that inside lanes merging allows for smoother flow. So, the question is, what do the numbers say? I wouldn't be surprised either way, so I'm genuinely curious here.

ETA: I've been looking around here and there, but so far I haven't found anything addressing this issue.

[jakeroot]

I'm fine with them on low-speed roads, but I'm a bit uncomfortable with them on high-speed roads.  With adequate signage, not such a huge deal, I suppose, but I'd still prefer a different design.

The main advantage seems to be higher capacity. I've noticed multi-lane ramps, where the outside lane ends after the merge, have lower usage of the ending lane (sometimes significantly so). In the inside-lane-merging style, there seems to be better distribution. Likely because (A) some drivers want to immediately merge left into 'faster' traffic, so they'll use the inside lane, but you also have (B) drivers using the outside, non-merging lane to avoid having to merge.

From using the one in Indianapolis that I linked earlier, the key seems to be a longer merge area/neutral zone.

[1995hoo]

Personally, I think it should be banned. Much safer to do an added lane for the two center lanes and then right/left lane ends

Do we know this, though? It could be that they're fairly common where I'm from, but to me they don't seem more dangerous than anything else.

Center-lane merging situations are usually difficult to post advance warning of since it seems to me they are often found on wide highways and drivers may miss a sign on the side of the road. When drivers reach the actual merging point and finally realize what's happening, they have to focus on three things at once: looking out for traffic merging from the through lane beside them, safely merging with the traffic from the merging lane, and keeping a safe distance from the traffic ahead of them. I'd err on the side of caution and say this is too much happening at once to be considered safe. However, I would make an exception for low-speed urban roads where there's less pressure, but only if there's a clearly visible merge sign providing advance warning.

All that makes sense, of course, but so does the idea that inside lanes merging allows for smoother flow. So, the question is, what do the numbers say? I wouldn't be surprised either way, so I'm genuinely curious here.

ETA: I've been looking around here and there, but so far I haven't found anything addressing this issue.

See Reply #20 quoting jeffandnicole's explanation of why the Jersey Turnpike uses center-lane merges.

[BrianP]

I'm fine with them on low-speed roads, but I'm a bit uncomfortable with them on high-speed roads.  With adequate signage, not such a huge deal, I suppose, but I'd still prefer a different design.

The main advantage seems to be higher capacity. I've noticed multi-lane ramps, where the outside lane ends after the merge, have lower usage of the ending lane (sometimes significantly so). In the inside-lane-merging style, there seems to be better distribution. Likely because (A) some drivers want to immediately merge left into 'faster' traffic, so they'll use the inside lane, but you also have (B) drivers using the outside, non-merging lane to avoid having to merge.

From using the one in Indianapolis that I linked earlier, the key seems to be a longer merge area/neutral zone.

Another possible advantage is the merging vehicles have a second option with the center merge.  If the right lane ends.  You have one choice which is merge left.  (Not counting the emergency use the shoulder option. Should it be counted? The shoulder is usually empty.) While with the center merge, merging vehicles can merge into the center lane or change lanes to the outer lane to which they are adjacent. Though I'm not sure if this is a true advantage.

[jakeroot]

I'm fine with them on low-speed roads, but I'm a bit uncomfortable with them on high-speed roads.  With adequate signage, not such a huge deal, I suppose, but I'd still prefer a different design.

The main advantage seems to be higher capacity. I've noticed multi-lane ramps, where the outside lane ends after the merge, have lower usage of the ending lane (sometimes significantly so). In the inside-lane-merging style, there seems to be better distribution. Likely because (A) some drivers want to immediately merge left into 'faster' traffic, so they'll use the inside lane, but you also have (B) drivers using the outside, non-merging lane to avoid having to merge.

From using the one in Indianapolis that I linked earlier, the key seems to be a longer merge area/neutral zone.

Another possible advantage is the merging vehicles have a second option with the center merge.  If the right lane ends.  You have one choice which is merge left.  (Not counting the emergency use the shoulder option. Should it be counted? The shoulder is usually empty.) While with the center merge, merging vehicles can merge into the center lane or change lanes to the outer lane to which they are adjacent. Though I'm not sure if this is a true advantage.

I was going to mention that in my post but couldn't figure out how to word it. Indeed, you do have two options: left, as would be intended, but you can bail right as well if totally necessary. Seems like it might be safer.

No doubt these would always be unusual, but I still don't see how unusual is bad. Or even how going above and beyond with signage would be necessary. I think arrows and "left lane merges" signage would be perfectly adequate.

[1995hoo]

I'm fine with them on low-speed roads, but I'm a bit uncomfortable with them on high-speed roads.  With adequate signage, not such a huge deal, I suppose, but I'd still prefer a different design.

The main advantage seems to be higher capacity. I've noticed multi-lane ramps, where the outside lane ends after the merge, have lower usage of the ending lane (sometimes significantly so). In the inside-lane-merging style, there seems to be better distribution. Likely because (A) some drivers want to immediately merge left into 'faster' traffic, so they'll use the inside lane, but you also have (B) drivers using the outside, non-merging lane to avoid having to merge.

From using the one in Indianapolis that I linked earlier, the key seems to be a longer merge area/neutral zone.

Another possible advantage is the merging vehicles have a second option with the center merge.  If the right lane ends.  You have one choice which is merge left.  (Not counting the emergency use the shoulder option. Should it be counted? The shoulder is usually empty.) While with the center merge, merging vehicles can merge into the center lane or change lanes to the outer lane to which they are adjacent. Though I'm not sure if this is a true advantage.

I was going to mention that in my post but couldn't figure out how to word it. Indeed, you do have two options: left, as would be intended, but you can bail right as well if totally necessary. Seems like it might be safer.

No doubt these would always be unusual, but I still don't see how unusual is bad. Or even how going above and beyond with signage would be necessary. I think arrows and "left lane merges" signage would be perfectly adequate.

https://goo.gl/maps/muvEURUujBgNj2W19

https://goo.gl/maps/8mHVeAhcE7Nweh7S9 <---click just beyond the overpass to see the actual merge point

[jakeroot]

I'm fine with them on low-speed roads, but I'm a bit uncomfortable with them on high-speed roads.  With adequate signage, not such a huge deal, I suppose, but I'd still prefer a different design.

The main advantage seems to be higher capacity. I've noticed multi-lane ramps, where the outside lane ends after the merge, have lower usage of the ending lane (sometimes significantly so). In the inside-lane-merging style, there seems to be better distribution. Likely because (A) some drivers want to immediately merge left into 'faster' traffic, so they'll use the inside lane, but you also have (B) drivers using the outside, non-merging lane to avoid having to merge.

From using the one in Indianapolis that I linked earlier, the key seems to be a longer merge area/neutral zone.

Another possible advantage is the merging vehicles have a second option with the center merge.  If the right lane ends.  You have one choice which is merge left.  (Not counting the emergency use the shoulder option. Should it be counted? The shoulder is usually empty.) While with the center merge, merging vehicles can merge into the center lane or change lanes to the outer lane to which they are adjacent. Though I'm not sure if this is a true advantage.

I was going to mention that in my post but couldn't figure out how to word it. Indeed, you do have two options: left, as would be intended, but you can bail right as well if totally necessary. Seems like it might be safer.

No doubt these would always be unusual, but I still don't see how unusual is bad. Or even how going above and beyond with signage would be necessary. I think arrows and "left lane merges" signage would be perfectly adequate.

https://goo.gl/maps/muvEURUujBgNj2W19

https://goo.gl/maps/8mHVeAhcE7Nweh7S9 <---click just beyond the overpass to see the actual merge point

These must be examples related to jeffandnicole's post about the NJ Turnpike on the last page.

I must say that a merging setup exactly like this is not something I've seen before (and based on the comments, it seems this is unique to the NJ Turnpike), but I'll be damned if it doesn't look like it works really well. Bit more signage than maybe I was thinking necessary, but then I have virtually zero first-hand experience with this setup.

I would hate to see the lane usage on the outside carriageway of the NJ Turnpike if all of those lanes merged into the #3 lane of the inner southbound carriageway. Current distribution of traffic looks very good from Street View imagery.

[ran4sh]

The New Jersey Turnpike is a special case though. Their arrangement is an attempt to compromise among 3 possibilities: both roadways open, left roadway closed, or right roadway closed. A configuration that avoids inside merging would result in some amount of thru traffic having to change lanes twice.

(I think that instead of such a merge, one lane could be dropped from each of the roadways at Exit 6 so that only 4 lanes instead of 6 lanes reach the merge point)

In the cases of a merge between different roads, having "thru traffic" from the minor route (i.e. not thru traffic from the perspective of the dominant route) change lanes twice would be safer than inside lane traffic not having any escape room if unable to merge.

[jakeroot]

In the cases of a merge between different roads, having "thru traffic" from the minor route (i.e. not thru traffic from the perspective of the dominant route) change lanes twice would be safer than inside lane traffic not having any escape room if unable to merge.

Would it though? I've not seen anyone here mention, with absolute certainty, that inside-lane merging is definitively less safe. I don't believe inside-lane merging is used to improve safety, granted, but the potential for danger seems mostly theoretical. Primarily, unfamiliarity with the setup could lead to dangerous situations. But the NJ Turnpike example is proof that even unfamiliar merging situations can be adequately marked and signed to the point of being perfectly manageable by drivers.

It's true that inside lane merging does not have that shoulder escape option** that an outside lane merge might have, but that's likely why most examples in this thread are exceptionally long. Long enough that not finding a merge point seems almost impossibly unlikely. And you'd still have the option of merging into the other lane; simply because it's another lane doesn't mean it will absolutely have cars in it.

** I've personally noticed that drivers are not necessarily keen to escape into shoulders, even when they should; I personally just witnessed a driver fail to find a gap on an on-ramp a couple days ago stop and wait for a gap, despite the availability of a shoulder that he could have used to merge. Why exactly a driver would rather stop in an active lane of traffic than drive a couple hundred feet in a shoulder is beyond me (I was waiting for him to get rear-ended), but drivers really don't seem keen on driving in shoulders. Apart from passing left-turning traffic, I suppose. Point being that having an escape option be another lane might actually be safer. But that's no more hypothetical than inside-lane merging being dangerous, so...yeah.

[interstatefan990]

^^ This is why I have a love-hate relationship with combined entry-exit ramps/weave lanes. They provide an escape for traffic that can't merge in time, allowing them to just continue to the exit and try again. But at the same time, they can be chaotic during periods of even slightly increased traffic levels, with several vehicles literally competing to merge into each other's spot all at once. I think traffic already on the freeway trying to take the exit technically has the right of way, but I'd be damned if I could find an everyday driver that actually knew that. Whenever I encounter this type of ramp, I always cross my fingers and hope no one is trying to enter while I exit or vice versa.

[SkyPesos]

What is the best way to sign an inside lane merge? This is how my example of Reagan Hwy onto I-275 SB earlier in this thread is signed, and I find it to be pretty good in terms of signage.

[webny99]

... most examples in this thread are exceptionally long. Long enough that not finding a merge point seems almost impossibly unlikely.

On the other hand, the fact that they're usually so long (presumably to allow more merging space) is another reason why I dislike them: they create ambiguity, and drivers tend not to react well to ambiguity especially on a fast-moving freeway.

[interstatefan990]

What is the best way to sign an inside lane merge?

I think that sign could be too easily mistaken as a triple added-lane with no merging necessary. This is my idea:

[kphoger]

I think traffic already on the freeway trying to take the exit technically has the right of way, but I'd be damned if I could find an everyday driver that actually knew that.

This is the sort of thing that would depend greatly on each state's vehicle code.  For example, in Illinois, both drivers are required to accommodate each other.  See below.

. . .Those on the highway have the right-of-way. . .

Not in Illinois.  Traffic in the on-ramp has the ROW and traffic on the Interstate must move over or slow down to accommodate.  Yup, I know, I was floored when I found out too.  No one here knows this so it's not really an issue until there's an accident and YOU end up with the ticket when you were just minding your own business in the right lane.

Who told you that?  What I see in the Illinois vehicle code is as follows:

(a) When 2 vehicles approach or enter an intersection from different roadways at approximately the same time, the driver of the vehicle on the left must yield the right-of-way to the vehicle on the right.

(b) The right-of-way rule declared in paragraph (a) of this Section is modified at through highways and otherwise as stated in this Chapter.

Notwithstanding the right-of-way provision in Section 11-901 of this Act, at an intersection where traffic lanes are provided for merging traffic the driver of each vehicle on the converging roadways is required to adjust his vehicular speed and lateral position so as to avoid a collision with another vehicle.

Basically, it is equally the responsibility of both drivers to make accommodation.

[ctkatz]

I was driving in a rented prius merging into 80 from the bishop ford 2 years ago. not being from illinois i was unaware of the merging area as well as the law that I had ROW in that situation.  I nearly got run off the road by a semi in stop and go traffic.  center merge lanes are dangerous especially since they are not a universal thing.  its probably safer to merge the lanes of the incoming road than center merge.