Lane Migration

[Sykotyk]

Okay, couldn't think of a better title. But, I hope it catches some attention.

Here's the thought. If you started at the 'official start' of a freeway in the right most lane, which lane number would you wind up in when you reach the 'official end' of the freeway?

For instance, the further right lane starts as Lane 0. The lane to the left is Lane 1. A 'slow truck' lane to the right opens up and is labeled 'Lane -1'
u. And so forth. As you travel down the road and lanes are either added or subtracted from the total.

If you drive down one road in Lane 0, and Lane 0, 1, 2, and 3 stay on one route, while you must change to Lane -1 to stay on that particular freeway, you are on Lane -1 when the exit ramp merges to the new roadway. If the ramp ends, you move back to Lane 0. If it puts you on the left side, you might wind up in Lane -1, while having Lane -2 and -3 to your right. Or, if the lane doesn't end, the new right most lane is now Lane -1, etc.

If you are in Lane -4 and a slow truck lane opens to your right, that's now Lane -5. But, when the top of the hill closes a lane, it closes the left most lane. Which makes -5 the new 'slow lane'.

I've kept track from time to time but always have gotten 'lost' or had to exit for a while and gotten off count, etc. Especially for long trips.

Curious if anyone else has ever thought of this, or had ever tried to keep track. I've always generally expected Lane 0 to eventually end at Lane 0 on the other end. However, that never seems to happen.

[Big John]

Depends on the engineering of the road.  Some agencies love having lane dropoffs and additions that make you change lanes all the time to stay on the mainline while others let you stay on the freeway without having to change lanes if you start in the left 2 or 3 lanes.  I strongly prefer the latter option as you don't have to change lanes in heavy traffic.

[Bickendan]

I-405, Portland, northbound:
At split from I-5, two lanes (1, 0) (I-5's "2, 1")
Exit 1A: Harbor Drive (left exit)
Ramp merge: I-5 south (2 right lane adds): Four lanes (1, 0, -1, -2)
Exit 1B: 4th Ave (right exit)
Exit 1C: 6th Ave (right lane drop): Three lanes (1, 0, -1)
Ramp merge: US 26 (west)/6th Ave (aux. lane add): Four (1, 0, -1, -2)
Exit 1D: US 26 Sunset Hwy/12th Ave (aux. lane drop): Three (1, 0, -1)
Exit 2A: Salmon St/14th Ave (right lane drop): Two (1, 0)
Ramp merge: US 26 (east) (aux. lane add): Three (1, 0, -1)
Exit 2B: Everett St (aux. lane drop): Two (1, 0)
Ramp merge: Couch St
Ramp merge: Glisan St (right lane add): Three (1, 0, -1)
Exit 3: US 30 west (left exit; left lane drop): Two (0, -1)
Ramp merge: US 30 East (2 left lane adds): Four lanes (2, 1, 0, -1)
Exit 4A: US 30 East/I-5 South (left exit): Four lanes (2, 1, 0, -1)
Exit 4B: Kerby Ave (right lane drop): Three lanes (2, 1, 0)
Mid ramp: Lane merge (left lane): Two lanes (1, 0)
Merge with I-5 north (as I-5's "-1, -2")

[froggie]

I've seen a few DOTs refer to it as "lane continuity", particularily in urban areas.  It was a cited issue with the old I-35W/MN 62 Crosstown Commons and I-35E/I-694 interchange areas before each was rebuilt, especially southbound 35W through the old Commons.

Speaking of which, northbound I-35W begins with 0 and 1 (-1 and 0 veer off to I-35E), becomes -1 and -2 at the downtown split, and ends with the same lane "-1", as lane -2 merges in just before the merge with I-35E.  Southbound I-35W begins with 0 and 1 (1 and 2 becoming I-35E) and ends with the same lane 1, but with lane 2...the lane 0 that SB 35W begins with becomes an exit-only lane for CSAH 42 just before the southern terminus.

[Alps]

OK, let's go to Boston.
Merge onto I-287, welcome to Lane 0.
Need to get over at NJ 208, Lane 1.
Merges with NJ 17, need to get over 1 lane for I-87, Lane 0.
Merges into mainline, Lane 1. Becomes the second-from-right lane across the Tappan Zee. Assuming continuity through the tollbooth, the third lane drops at the next exit, so I'm in the right lane once again. I could stay where I am for the Saw Mill River Parkway, but the fastest way is via the southern route, so...
Need to get over 1 lane for I-287, Lane 2.
Lane drops at I-95, need to get over, Lane 3. (I prefer CT Turnpike to the Merritt, if no traffic.)
Two lanes end after the merge, Lane 5.
Exit to Milford Parkway, Lane 4.
Merge onto the Parkway, Lane 5. Lane drops to Wilbur Cross, no action needed.
Need to get over 1 lane, Lane 6. Lane drops to I-91, no action needed.
Need to get over 1 lane, Lane 7.
Exit to CT 15, Lane 6.
Merge into CT 15, Lane 7. I'm now in the second-left lane of I-84.
Six lanes approach the I-90 toll plaza, three lanes leave, so assuming a 2 to 1 continuity, I need to move right 1 lane, Lane 6. Lane adds to I-90, no action needed.

So I've gone from Lane 0 to Lane 6 on a fairly normal drive, on a common route. (If you protest that I didn't subtract 1 for exiting in Boston, note that I didn't add 1 for entering in NJ.)

[Scott5114]

This is kind of confusing because when lanes are numbered, I've always seen the far left lane referred to as the #1 lane.

[Sykotyk]

True. But, that's more the 'left to right' reading the English language (and most Western languages employ). But, the right lane is the default lane. It's the drive line in a multi-lane highway. Passing goes to the left. So, it's the 'additional' lane. Therefore, +1. Slow lanes, etc end up being -1 because their purpose is strictly for going slower than the normal traffic in the default lane of travel.

Lane Continuity works as a term. Thought there might be a name out there. If you're in Lane 0 on I-80, you should be able to stay on I-80 the whole way.Overlaps do cause problems. But usually that's a slip ramp to the right and you merge back from the right into what becomes new Lane 0 after the merge. Tennessee, for example, does it badly at both Memphis and Nashville. Way too much weaving to stay on the same road.

[NE2]

The overlap in downtown St. Paul is perfect for lane continuity.

[bzakharin]

The worst offender I've been on is I-76 from its start in NJ to where it becomes the PA Turnpike. If I start in lane 0 from 295 South, I have to go to lane 3 in order to stay on 76 where 676 splits off. On the Walt Whitman Bridge a right lane merges in. I'm on lane 3 which is locally lane 1. Assuming continuity through tolls, eventually both the right and left lanes exit, so I'm on lane 0 again. Alas, my lane ends, so the new lane 0 is my lane 4. My new lane exits at exit 346B, so the new lane 0 is now my lane 5. A lane comes in from the right at exit 341, so I'm now in lane 1, but I have to move left again at 340B where the new lane 0 is now my lane 6. That pretty much ends the craziness, but I just moved 6 lanes to the left over the course of 20 miles just to stay on the same highway.

[agentsteel53]

I-15 northbound is already at lane 4 (or 5?) within 10 miles of its terminus, due to the influx of CA-163 on the left.