NY - Sequential vs. Mile Based Exits

[Rothman]

Exit 3 on the Northway is coming.

[cl94]

Exit 3 on the Northway is coming.

They've been saying that for 20 years  .

[empirestate]

That's not what I'm saying, per se. I'm saying it would stop the "oh, crap, my exit is coming up!" you get now. In most of the country, an exit number difference of 1 implies the exits are a mile apart and most people act accordingly.

I guess I don't quite follow you, then. In a sequential system, the numbers are always 1 apart, so you'd think motorists would be constantly ready for their exit, always thinking it was a mile away.

This cracked me up  You've basically just helped summarize a major issue with sequential numbering.[/quote]

Who, me or cl94? Or both of us?

Advance signage is only usually posted a mile in advance; it rarely overlaps the previous interchange in rural areas. As such, the average motorist/tourist has no idea when their exit will be, only that it's 60, and therefore must come after 59. If they're in the left lane expecting a long distance and suddenly those two exits are in quick succession - then crap - we have a problem.

Right, but if they're accustomed to mile-based numbering, then they'd tend to think 59 and 60 are closer together than they might actually be. So I don't see why there'd be a problem with exits coming up too quickly?

OK. Let me phrase it this way. Sequential numbering has no problems on its own merits - it works, it serves its purpose, and people make do. It's fine - some of us could proabably use it forever without batting so much as an eyelash. But it just so happens that it's inferior; there's a much better, more advanced, universally accepted, solution.

Similarly, there's no "problem" with typewriters. At some point, you come to grips with the fact that even though the typewriter is still in mint condition, working great, you should invest in a computer. It should be obvious -
it doesn't have to be broken before it's worth considering an upgrade. Progress is inevitable; an integral part of the world we live in. Like it or lump it, it's happening before your very eyes.

And that, in raw, simplistic terms, is the real crux of the issue with the stance that there isn't a problem.

Right, and that crux leads you to believe a conversion is necessary, and me to believe that it isn't. Pages and pages later, we still come back to that simple subjective decision. But it looks like you're still holding out for trying to persuade me, so maybe the simplest way to put is is this: Is there something you think I've got wrong? Some point I haven't grasped that, if I did, would lead me to change my view?

A variation of this problem with some (not all) sequential numbering schemes is skipped numbers.  Pass Exit 58, bed in for a cruise, mile . . . mile . . . OMG, next exit is 60! (often because Exit 59 exists only in the other direction).  And this can surprise even the wary driver who is prepared for a rapid-fire succession of exits.

But of course, this situation exists with all mile-based systems. So, if it's a problem, it's one that's less likely to exist in a sequential system.

Especially the absence of 22, since 21 is a major double-split junction with I-590. Combined with the lack of advance signage for 21, this leads to a lot of last minute weaving. Here all these years people have been merging right at the last second, and I've been blaming them for intentionally cutting the queue 

I've always attributed this kind of last minute weaving to each driver's belief that he is better than everyone else at being faster than everyone else, and therefore expects to arrive at each exit ahead of any other given vehicle. Has this kind of behavior been shown to exist less in mile-based areas?

Also, what about the Thruway case south of Albany? Say you're going NB and looking for 21B. Think it'll be after 21A? Nope! The sequence is 21-21B-21A-22. And 22 is less than a mile north of 21A.

Yup, as I said before, that's an example of something I'd consider a much bigger problem than the lack of a mile-based system. You could quite easily persuade me that changing this is worthwhile.

[Rothman]

Exit 3 on the Northway is coming.

They've been saying that for 20 years  .

Butbutbut NYSDOT did Phase 1 already!

[kalvado]

Exit 3 on the Northway is coming.

They've been saying that for 20 years  .

Butbutbut NYSDOT did Phase 1 already!

OK, so it is one phase per 20 years?

[J N Winkler]

Right, but if they're accustomed to mile-based numbering, then they'd tend to think 59 and 60 are closer together than they might actually be. So I don't see why there'd be a problem with exits coming up too quickly?

This is not the problem Cl94 is talking about.  The issue is drivers accustomed to sequential systems inside cities (where exit spacing is typically at or close to the one-mile minimum) cutting back in unnecessarily to take an exit that they think is coming up in less than a mile when in fact there are many more miles still to go.

This issue does not surface with mileage-based exit numbering because then the difference in exit number corresponds to the actual distance between the exits.

A variation of this problem with some (not all) sequential numbering schemes is skipped numbers.  Pass Exit 58, bed in for a cruise, mile . . . mile . . . OMG, next exit is 60! (often because Exit 59 exists only in the other direction).  And this can surprise even the wary driver who is prepared for a rapid-fire succession of exits.

But of course, this situation exists with all mile-based systems. So, if it's a problem, it's one that's less likely to exist in a sequential system.

No.  Sequential exit numbering has the potential to create a false expectation of one-by-one progression in exit number from one exit to the next.  With mileage-based exits, there is no such expectation.  Both systems are equally susceptible to the problems that arise from an exit that exists in only one direction being shown on a map in exactly the same way as an exit that exists in both directions.

Also, what about the Thruway case south of Albany? Say you're going NB and looking for 21B. Think it'll be after 21A? Nope! The sequence is 21-21B-21A-22. And 22 is less than a mile north of 21A.

Yup, as I said before, that's an example of something I'd consider a much bigger problem than the lack of a mile-based system. You could quite easily persuade me that changing this is worthwhile.

Then on that basis you should support a change to mileage-based exit numbering.  Barring (very unusual) major changes in freeway centerline alignment, mileage-based numbers are futureproofed, cannot be out of sequence, and cannot create a false expectation that Exit X + 1 exists and follows Exit X.

[webny99]

This cracked me up  You've basically just helped summarize a major issue with sequential numbering.

Who, me or cl94? Or both of us?

Cl94 was trying to summarize the issue, and you helped, as summarized by JN in the first paragraph of his post above. Anyways, moving on...

Right, but if they're accustomed to mile-based numbering, then they'd tend to think 59 and 60 are closer together than they might actually be. So I don't see why there'd be a problem with exits coming up too quickly?

The point is that they have no idea how far apart the exits are. On a road like the Northway, it can go either way. They can be overly prepared and hang out on the right for twenty miles, or they can zip right by 59 (or 58  ) without realizing that 60 is quite close.

Right, and that crux leads you to believe a conversion is necessary, and me to believe that it isn't. Pages and pages later, we still come back to that simple subjective decision.

I guess I fail to see how it's even subjective; in the same way that I'd fail to understand you continuing to use a typewriter when someone offered you a computer.

But it looks like you're still holding out for trying to persuade me, so maybe the simplest way to put is is this: Is there something you think I've got wrong? Some point I haven't grasped that, if I did, would lead me to change my view?

I don't know what to say. I mean, you say you don't have a position because there's no problem, but that just seems like an obsolete stance to take. It really doesn't matter if there's a problem with the current system or not; if there's something better, why not go for it?

A variation of this problem with some (not all) sequential numbering schemes is skipped numbers.  Pass Exit 58, bed in for a cruise, mile . . . mile . . . OMG, next exit is 60! (often because Exit 59 exists only in the other direction).

But of course, this situation exists with all mile-based systems. So, if it's a problem, it's one that's less likely to exist in a sequential system.

JN has discussed this above, but with a mile-based system, drivers expect missing numbers.

Also, what about the Thruway case south of Albany? Say you're going NB and looking for 21B. Think it'll be after 21A? Nope! The sequence is 21-21B-21A-22. And 22 is less than a mile north of 21A.

Yup, as I said before, that's an example of something I'd consider a much bigger problem than the lack of a mile-based system. You could quite easily persuade me that changing this is worthwhile.

This could not possibly occur with a mileage based system, as I'm sure you're aware 

[seicer]

Oh. My. God. Please stop already. Not everyone has to like your posts or has to like your position.

[vdeane]

I don't know what to say. I mean, you say don't have a position because there's no problem, but that just seems like an obsolete stance to take. It really doesn't matter if there's a problem with the current system or not; if there's something better, why not go for it?

Some people take the view "if it ain't broke, don't fix it".  This entire thread can be boiled down to that sentence and the quoted bit.

[jp the roadgeek]

This is still going on back and forth?  Ok, maybe there needs to be a visual of how the Thruway mainline would look with mileage based exits, using individual highway mileage in the second column and Thruway mainline mileage.  For individual highways, I left 24 unnumbered because each ramp is part of a mainline highway (I-87 going orth, I-90 going east).  You be the judge which works best.

CURRENT                                   INDIV.                        INTRN.
1                                          9 (A SB)                        1(A SB)
2                                          9B                                1B
3 (NB)                                  10A                                2A
4                                          10B                                2B (2 B-A SB)
5                                          11                                 3
6 (N/S SB)                                  12 (A/B SB)                 4 (A/B SB)
6A                                          13                                 5
7                                          16                                 8
7A                                          19                                 10
8                                          20 (A SB)                         11
8A                                          20B                                 12
9                                          21                                 13
10                                          25                                 17
11                                          26                                 18
12                                          27                                 19
13 N/S                                  29 A/B                         21 A/B
14                                          31                                 23
14A                                          32                                 24
14B                                          36                                 28
15                                          38                                 30
15A                                          40                                 31
16                                          54                                 46
17                                          68                                 60
18                                          84                                 76
19                                          100                                 91
20                                          110                                 101
21                                          122                                 114
21B                                          133                                 125
21A                                          142                                 134
22                                          143                                 135
23                                          150                                 142
24                                          NO #                                 148
25                                          343                                 154
25A                                          337                                 159
26                                          334                                 162
27                                          322                                 174
28                                          314                                 182
29                                          302                                 194
29A                                          285                                 211
30                                          276                                 220
31                                          264                                 233
32                                          253                                 243
33                                          243                                 253
34                                          235                                 262
34A                                          219                                 277
35                                          217                                 279
36                                          213                                 283
37                                          212                                 284
38                                          210                                 286
39                                          206                                 290
40                                          192                                 304
41                                          176                                 320
42                                          169                                 327
43                                          156                                 340
44                                          149                                 347
45                                          145                                 351
46                                          134                                 362
47                                          117                                 379
48                                          106                                 390
48A                                          94                                 402
49                                          79                                 417
50                                          76                                 420
50A                                          75                                 421
51 E/W                                  74 A/B                         422 A/B
52 E/W                                  73 A/B                         423 A/B
52A                                          71                                 425
53                                          70                                 426
54                                          68                                 428
55                                          67                                 429
56                                          64                                 432
57                                          60                                 436
57A                                          51                                 445
58                                          40                                 456
59                                          29                                 468
60                                          11                                 485
61                                          1                                 495

B1                                            368*                                7
B2                                            377                                  15
B3                                            385                                  23

*= number is assigned to ramp from Free 90 EB to WB spur, EB spur to WB Free 90, and WB spur for thru traffic, as the current B1 ramp is part of the 90 mainline. 

[webny99]

Especially the absence of 22, since 21 is a major double-split junction with I-590. Combined with the lack of advance signage for 21, this leads to a lot of last minute weaving. Here all these years people have been merging right at the last second, and I've been blaming them for intentionally cutting the queue 

I've always attributed this kind of last minute weaving to each driver's belief that he is better than everyone else at being faster than everyone else, and therefore expects to arrive at each exit ahead of any other given vehicle.

This is really a separate discussion entirely, hence the separate post.

I do believe there are certain drivers who think they have priority over everyone, and that everyone else must be subject to their rip-roaring, queue-cutting behavior. There are enough of these drivers that use the aforementioned intersection that I find myself irked at times, and in fact on several occasions have taken to my horn and the gas pedal to shut them out.

However, I don't think all drivers are motivated by the desire to beat everyone else, nor by the belief that they can. In fact, JNWinkler's post regarding missing sequential numbers was very enlightening (even to me) in this regard. I now see that drivers unfamiliar with I-490 could easily end up acting like the budgers I so despise, and yet it is no fault of their own - they were expecting an exit 22 when there was none, and were not prepared to take the exit, much less join the end of a forming queue. The lack of signage, which I mentioned in passing, adds to this dilemma, since the first advance warning is a mere half-mile away.

Has this kind of behavior been shown to exist less in mileage-based areas?

Well, New York is the source of all aggressive drivers, so data aside, convential wisdom says yes 
We have the "me first" drivers as well as the "crap - here's my exit" drivers. Many other states have neither - they have both mileage-based exits and more polite drivers, virtually eliminating this behavior.

[seicer]

Was a decision ever made about the mainline Thruway exit numbers for when the state goes mileage based? No one drives (well, no one should) drive the Thruway in its entire length, so the use of mileage-based exits exclusive for the mainline Thruway would be impractical. At worse, it would result in a haphazard numbering scheme that's even more confusing than what's out there now. The system-only exit scheme doesn't work well in its current form, nor does it work well for the New England Thruway/Interstate 95 which is a bureaucratic mess.

Just imagine of the Kentucky Turnpike, which was sequentially based, still had Exit 1 in Elizabethtown in 2018!

[webny99]

I don't know what to say. I mean, you say you don't have a position because there's no problem, but that just seems like an obsolete stance to take. It really doesn't matter if there's a problem with the current system or not; if there's something better, why not go for it?

Some people take the view "if it ain't broke, don't fix it".  This entire thread can be boiled down to that sentence and the quoted bit.

I fully agree. I should have used that wording eight pages ago 

[empirestate]

Right, but if they're accustomed to mile-based numbering, then they'd tend to think 59 and 60 are closer together than they might actually be. So I don't see why there'd be a problem with exits coming up too quickly?

This is not the problem Cl94 is talking about.  The issue is drivers accustomed to sequential systems inside cities (where exit spacing is typically at or close to the one-mile minimum) cutting back in unnecessarily to take an exit that they think is coming up in less than a mile when in fact there are many more miles still to go.

I see. And to be honest, I've already forgotten the difference between this and whatever I was thinking. Anyhow, definitely still in the not-really-a-problem category for me.

A variation of this problem with some (not all) sequential numbering schemes is skipped numbers.  Pass Exit 58, bed in for a cruise, mile . . . mile . . . OMG, next exit is 60! (often because Exit 59 exists only in the other direction).  And this can surprise even the wary driver who is prepared for a rapid-fire succession of exits.

But of course, this situation exists with all mile-based systems. So, if it's a problem, it's one that's less likely to exist in a sequential system.

No.  Sequential exit numbering has the potential to create a false expectation of one-by-one progression in exit number from one exit to the next.  With mileage-based exits, there is no such expectation.  Both systems are equally susceptible to the problems that arise from an exit that exists in only one direction being shown on a map in exactly the same way as an exit that exists in both directions.

Ah–nobody had mentioned the expectation part of it yet. That's the real problem, then: the expectation, not the skipping of numbers per se. If–once again–it's actually a problem.

Also, what about the Thruway case south of Albany? Say you're going NB and looking for 21B. Think it'll be after 21A? Nope! The sequence is 21-21B-21A-22. And 22 is less than a mile north of 21A.

Yup, as I said before, that's an example of something I'd consider a much bigger problem than the lack of a mile-based system. You could quite easily persuade me that changing this is worthwhile.

Then on that basis you should support a change to mileage-based exit numbering.  Barring (very unusual) major changes in freeway centerline alignment, mileage-based numbers are futureproofed, cannot be out of sequence, and cannot create a false expectation that Exit X + 1 exists and follows Exit X.

I don't understand how that follows. Because one thing is a bigger problem than another thing, I should support solving both things?

Right, and that crux leads you to believe a conversion is necessary, and me to believe that it isn't. Pages and pages later, we still come back to that simple subjective decision.

I guess I fail to see how it's even subjective; in the same way that I'd fail to understand you continuing to use a typewriter when someone offered you a computer.

That's basically it, yes. I'm able to understand that, so I'm able to arrive at that different viewpoint.

But it looks like you're still holding out for trying to persuade me, so maybe the simplest way to put is is this: Is there something you think I've got wrong? Some point I haven't grasped that, if I did, would lead me to change my view?

I don't know what to say. I mean, you say you don't have a position because there's no problem, but that just seems like an obsolete stance to take. It really doesn't matter if there's a problem with the current system or not; if there's something better, why not go for it?

Because it's not worth the undertaking. I get that you don't see it my way, and that's fine; I'm not asking you to. But that's how I see it!

21-21B-21A-22

This could not possibly occur with a mileage based system, as I'm sure you're aware 

Of course. But again, it's not worth changing the whole system over just to fix these two exits.

Oh. My. God. Please stop already. Not everyone has to like your posts or has to like your position.

Hehe–persistent, ain't they? To be fair, that is the whole reason this thread exists as it was split off from another topic. (Though maybe the subject line should be changed to more accurately reflect that–ah, there we are, that's better.)

But yeah, I'm hoping it's about time to wind down, now. And to be honest, it's probably been a little while now since I reached the point of purposely not changing my mind under any circumstances, just because.

EDIT: And just in case anyone's still holding out hope about swaying me, I've been clinging fast to my opinion for at least 18 years...and that means I'm now 18 years older and stodgier.
https://groups.google.com/forum/#!searchin/misc.transport.road/nw$20perry$20sequential$20numbering%7Csort:date

[webny99]

Well, you can't say I wasn't persistent in my appeals to logic and reason and common sense 
If I didn't admire you so much for sticking to your guns, I'd call you nothing other than stuck in a rut. And to keep that narrow-minded viewpoint is your loss.

My final effort, if I were to make one, would be to minimize the size of the undertaking in your mind. It must loom far larger than life to you, but I'd best not try to change that - the rest of us know $2.5 million is as a drop of water in the mighty Mississippi 

I've offered several other tangents in this thread not directly related to persuading you to have a change of opinion. If any of those pick up, I may be back, but for now, 

[J N Winkler]

But yeah, I'm hoping it's about time to wind down, now. And to be honest, it's probably been a little while now since I reached the point of purposely not changing my mind under any circumstances, just because.

I wonder if this discussion would have gone on as long as it has if you had indicated early on--perhaps even at the start--that you were not persuadable on this issue, and had undertaken to make that your last post in the thread.  Sometimes it is kinder not to encourage others to keep on rolling the dice.

[seicer]

Well, you can't say I wasn't persistent in my appeals to logic and reason and common sense 
If I didn't admire you so much for sticking to your guns, I'd call you nothing other than stuck in a rut. And to keep that narrow-minded viewpoint is your loss. [...] I've offered several other tangents in this thread not directly related to persuading you to have a change of opinion. If any of those pick up, I may be back, but for now, 

Let's have a big eye roll here. Stop being obtuse and obsessive about this topic. I'd love to continue this discussion as I have other relevant tangents I'd love to discuss, but it keeps getting drowned out in a cascade of quotes and posts that drags an entire conversation down.

[Alps]

Well, you can't say I wasn't persistent in my appeals to logic and reason and common sense 
If I didn't admire you so much for sticking to your guns, I'd call you nothing other than stuck in a rut. And to keep that narrow-minded viewpoint is your loss. [...] I've offered several other tangents in this thread not directly related to persuading you to have a change of opinion. If any of those pick up, I may be back, but for now, 

Let's have a big eye roll here. Stop being obtuse and obsessive about this topic. I'd love to continue this discussion as I have other relevant tangents I'd love to discuss, but it keeps getting drowned out in a cascade of quotes and posts that drags an entire conversation down.

Then continue the goddamn conversation any way you please. It's a forum, not a room. You can post what you like and people will respond to it. Stop being obtuse and obsessive about denigrating other forum members.

[empirestate]

But yeah, I'm hoping it's about time to wind down, now. And to be honest, it's probably been a little while now since I reached the point of purposely not changing my mind under any circumstances, just because.

I wonder if this discussion would have gone on as long as it has if you had indicated early on--perhaps even at the start--that you were not persuadable on this issue, and had undertaken to make that your last post in the thread.  Sometimes it is kinder not to encourage others to keep on rolling the dice.

I'm thinking it would have...webny99 seems quite dedicated to the cause.

But, to be sure, it wouldn't have been accurate early on to say that I was unpersuadable: I've been genuine in everything I've said about not seeing it as a problem, not being worth the value to convert, etc. And believe it or not, this whole time I've been thinking hard about what exactly you all might say, what new perspective you could provide, that would change my mind. I only started to feel intentionally stubborn at the end, as the conversation started to lose its novelty and I needed some way to stay interested in it.

And, in truth, I was actually a bit surprised at myself to read how obstinate I was about the subject way back in the MTR days...kidding aside, it appears I'm actually more open-minded about it now–or at least more fair-minded–than I was then. I guess I've had a lot of time over the years to actually justify my position to myself, and I think I've done a pretty good job of that. :-)

So yeah, I had every of intention of being persuaded, if possible, until a page or so ago; and of course, I'll still consider any earth-shattering new perspective that might come up in the future. Otherwise, it's only fair to state that the threshold for persuasion has now officially closed for me.

[roadman65]

Dont all be surprised at this one.  We had that diesel mechanic from Chicago on here who kept threads going on as long as this one, however most would end as moderators would get tired of insult trading and lock them.

One thing from what I have read, this guy is not like the other user and hitting hard words and insulting people outside of Chicago and those who do not see the need for the Edens Spur to have full interchanges and of course that hypotenuse nonsense. 

[webny99]

So yeah, I had every of intention of being persuaded, if possible, until a page or so ago.

Is the timing a coincidence? I think not

Dont all be surprised at this one.  We had that diesel mechanic from Chicago on here who kept threads going on as long as this one, however most would end as moderators would get tired of insult trading and lock them.

This has not involved insult trading; both parties are too mature for that 

One thing from what I have read, this guy is not like the other user and hitting hard words and insulting people outside of Chicago and those who do not see the need for the Edens Spur to have full interchanges and of course that hypotenuse nonsense. 

And now this will open up a whole new can of worms, and I'll sit back and watch and see what everyone else has to say about me. 

[roadman65]

 :DNo I actually complimented you.   You did not trade insults at all, but you have to remember this that many subjects die early and many on here want to move on.  Not to be a critic at you was not the intention, but others have to also see some bright sunny skies in some of what they may think is the worst.

To me personally I will let NY deal with their own problems.  I do not live there, and despite the fact mile based numbering is my preference, its not that dyer of a need to change over for me.  So I could care less about this whole thing.  Yes its a good topic, but not one that is on top of a list of priorities for me (and for others I will guess as well). 

Post as you like as long as you stay within the bounds.

[J N Winkler]

Over the past few pages, I have personally been trying to move beyond the specific topic of applying mileage-based exit numbering to the freeways in New York that currently have sequentially numbered exits, and look more generally at the wrinkles in both systems.  Here are a few issues that might provide seeds for more productive discussion:

Unbuilt mileage to zero point

One of the arguments traditionally advanced for sequential exit numbering is a lower likelihood of subsequent renumbering being needed in cases where a route has unbuilt mileage toward its zero point.  The underlying rationale is that it is easier to determine access points along an unbuilt length than it is to identify a centerline for milepointing purposes that will not subsequently be altered for reasons not known or knowable at the planning stage, such as adverse ground conditions and the like.

How many examples are there actually of freeways that have had mileage-based exit numbers adjusted as a result of ultimately built length being greater or less than originally projected?  In this thread two examples have been presented:  I-10 in Arizona (2 1/4 miles longer than originally projected, exit numbers not adjusted), and I-15 in Utah (3 miles shorter than projected, exit numbers adjusted).  Are there any others?  Is it a fair generalization that the "trigger point" for renumbering exits is milepointing being off by, say, 2 3/4 miles?  Are there any precedents for discrepancies in milepointing arising otherwise than by locating the freeway in a corridor several miles away from what was initially planned?

Relation of choice of exit numbering system to completion percentage of ultimate freeway network

The stylized fact is that as the freeway network in the US has aged, with original Interstate construction tailing off as outstanding segments are completed and relatively little new freeway being built on an ongoing basis, state DOTs have been converting from sequential to mileage-based exit numbering.  It is usually assumed that this is because as the freeway network in a given state matures, the risk of centerline mileage along a given freeway changing goes down, and state DOTs become more willing to accept an ever-smaller risk of having to renumber exits.

This raises several questions.

First, how common is it that exits are actually renumbered under either sequential or mileage-based schemes, aside from Interstate redesignations like I-376 in Pennsylvania, I-295 around the I-95/Turnpike interchange, I-785 in North Carolina, etc.?

Second, what strategies have state DOTs used in cases where it is desirable to have exit numbers on certain freeways that are essentially complete but others are largely unfinished?  One approach I have been told was common (in Arizona, Ohio, etc.) was for temporary signing to be erected, either by state forces or by the paving contractor for a given segment, that omitted exit numbers.  Then, when the freeway was finished, a single permanent signing contract would be let to remove all the temporary signs and install new ones with exit numbers.  Another approach (favored by Georgia) was to install the permanent signing, including blank exit tabs, as part of the paving, and then come back later and populate the blank exit tabs with exit numbers once the freeway was finished (or firmly located) throughout its entire corridor.

Have any state DOTs have ever gone from mileage-based to sequential exit numbering?  ISTR it being reported in MTR (but have not myself confirmed) that Georgia originally had mileage-based numbers, went to sequential in the 1970's, and converted back to mileage-based around 2000.  I also suspect (but have not confirmed) that when Colorado abandoned a dual-posting system, the initial transition was to sequential exit numbering only, with a conversion to mileage-based exit numbering following a few years later.

Actual prevalence of revising sequential exit numbers

Two main strategies exist for accommodating new exits on a freeway with sequentially numbered exits:  reserving unused numbers for exits thought likely to be added in the future (often with the result that gaps in numbering persist for decades), and assigning suffixed numbers to the new exits.  Are there any cases of freeways having their exit numbers changed wholesale to accommodate new exits or clean up longstanding jumps in exit number?

Dual posting

How many states experimented with dual-posting systems and, besides the added cost and message loading, what were their reasons for ultimately abandoning them?

[vdeane]

I-40 in TN is 4 miles longer than originally planned because of Overton Park.  The exit numbers were not adjusted.

The NYSDOT and PANYNJ portions of I-95 have mile-based numbers; about 15 years ago, NYSDOT tried and then aborted a conversion to sequential numbers.  The northbound PANYNJ portion still has the sequential numbers (SB 1 finally changed back to 1A as part of the Alexander Hamilton Bridge project).

I believe I've read that RI experimented with dual posting.  No idea why it was ended.

Not aware of any wholesale sequential renumberings, but I am aware of a minor one.  On NY 17/I-86, when the new exit east of Lowman was opened, exit 58 was renumbered to 57 and the new exit became exit 58.  I-278 also has a partially done renumbering (since cancelled I think, so there's a permanent gap between 35 and 39), though that wasn't because of new interchanges, but because of interchanges that had the same number were to be renumbered to have separate numbers (29A and 29B would have become 30 and 31, for example) (old I-278 (assuming I didn't get any numbers wrong) and current I-278).

[machias]

I-40 in TN is 4 miles longer than originally planned because of Overton Park.  The exit numbers were not adjusted.

The NYSDOT and PANYNJ portions of I-95 have mile-based numbers; about 15 years ago, NYSDOT tried and then aborted a conversion to sequential numbers.  The northbound PANYNJ portion still has the sequential numbers (SB 1 finally changed back to 1A as part of the Alexander Hamilton Bridge project).

I believe I've read that RI experimented with dual posting.  No idea why it was ended.

Not aware of any wholesale sequential renumberings, but I am aware of a minor one.  On NY 17/I-86, when the new exit east of Lowman was opened, exit 58 was renumbered to 57 and the new exit became exit 58.  I-278 also has a partially done renumbering (since cancelled I think, so there's a permanent gap between 35 and 39), though that wasn't because of new interchanges, but because of interchanges that had the same number were to be renumbered to have separate numbers (29A and 29B would have become 30 and 31, for example) (old I-278 (assuming I didn't get any numbers wrong) and current I-278).

I-690 was completely renumbered from sequential to sequential back when the new interchange with the Thruway was built, 1988 or so?  I think the numbers shifted by 5 and the interchange with I-81 still did not receive a number at that time. You can see the overlays on the folded up signs used during the State Fair.