Interstate Highway Numbering Nonsense

[MultiMillionMiler]

Yes I know that's what they mean, and there's no point to that. Why do they need to match the mile markers?

Well, they don't have to.  But, if you're looking for Exit #114, and you're at mile marker 127, it's a handy way of figuring out you're 13 miles from your exit.

How is that not blatantly obvious?

The adding new exits later on is blatantly obvious, I just didn't think of it for some reason, but why would you have to know the distance to your exit? Signs will label the exit ahead of time. You can also just set your tripodometer if you have done the route before, of you know the mileage ahead of time, and just do some simple math as you go along.

[kphoger]

why would you have to know the distance to your exit?

– Daddy, when's lunch?
– Honey, check the map.  What exit number is Alantown?
– 191.
– OK, we're at mile marker 241, so that's ... 50 miles ... We're about 40 minutes away, guys, so around 12:35.

or

– The gas light just came on.  Honey, how far is it to Alantown?
– The map says it's at Exit #191.
– OK, we're at mile marker 241, so that's ... hmmm, it doesn't look like we can make to the truck stop in Alantown.
– I just saw a billboard back there saying there's a Super-Sbarro gas station at Exit #220.
– Cool.  We'll fill up there instead.

[Scott5114]

If I know I need to exit at Exit 300 and I'm at MM 258, I know I can assuredly pass a long string of trucks and have enough time to get in the right lane before my exit. But if I'm at MM 298, I might be better off hanging back and just driving slower since my exit is in only 2 miles. (Sure, there should be a 2-mile sign, but...well...New Mexico has interstates too.)

Also, providing distance data to drivers has been part of American signage since before the car. Hand-painted signs for destinations and mileages were commonplace signage for horse-drawn carriages in the 19th century. Later, in the 1910s, when ACSC was posting the first road signs intended for automobile use in California, they were already putting distance information on them. (In the photos, the diamond-shape signs came first, in the 1910s or so, and then in the 1920s-1930s they changed to rectangular ones.)

(photos by Max Rockatansky)



And it's not just the US, either. Pretty much every country has a specification for a distance information sign that appears after major highway junctions.

[Bruce]

Most rural interstates shouldn't be mile based. That is one serious flaw in the numbering system. There is no logic or benefit in that whatsoever, just pure OCD. It's like saying I-90 must have exactly 90 exits in each state, or that I-70 must have exactly 70 exits in each state.

Mile-based exit numbers are at their most useful in rural areas where they can be used to easily calculate distance. This argument makes no sense.

[Max Rockatansky]

@Scott

Out of curiosity, been talking to Alps about Laws Depot? 

[Amaury]

Mile-based exit numbers are at their most useful in rural areas where they can be used to easily calculate distance. This argument makes no sense.

Agreed. They have been going too far in that direction and suggesting things like eliminating interstate designations, which is why I said I don't really agree with them, either.

[Quillz]

A counter argument was not offered: if rural interstates shouldn't have mileage-based exits, what should the exit numbers be based off of?

[Max Rockatansky]

A counter argument was not offered: if rural interstates shouldn't have mileage-based exits, what should the exit numbers be based off of?

There is probably a better argument for not having exit numbers at all out west versus going back to sequential numbers. 

[kphoger]

A counter argument was not offered: if rural interstates shouldn't have mileage-based exits, what should the exit numbers be based off of?

the greek alphabet

[kirbykart]

A counter argument was not offered: if rural interstates shouldn't have mileage-based exits, what should the exit numbers be based off of?

There is probably a better argument for not having exit numbers at all out west versus going back to sequential numbers.

What do you mean "out west"? Plenty of rural spots in the east too, like the thirty-mile gap on the Mass Pike I mentioned earlier.

If I know I need to exit at Exit 300 and I'm at MM 258, I know I can assuredly pass a long string of trucks and have enough time to get in the right lane before my exit. But if I'm at MM 298, I might be better off hanging back and just driving slower since my exit is in only 2 miles. (Sure, there should be a 2-mile sign, but...well...New Mexico has interstates too.)

Since when has a two-mile sign been necessary? Say you're travelling at 70 mph; you still have almost a whole minute till the exit from the one-mile advance. I don't see the reason for a 2-mile sign, with one exception: major freeway-to-freeway junctions. These could have advances 10 miles back for all I care. But 2-mile advances build up anticipation of reaching the exit much more quickly than you actually will, and really there is plenty of time to move over to the right lane (which you should already be in unless you were passing someone) and make your exit from the one-mile advance sign.

This is one of the few instances in which New Mexico has done something correctly.

[kphoger]

Since when has a two-mile sign been necessary? Say you're travelling at 70 mph; you still have almost a whole minute till the exit from the one-mile advance.

Back when I drove an Isuzu cab-over box truck, it would have been nice.  With the pedal to the metal, it would top out at just over 70 mph–although I did once get it up to 77 mph on a long downhill with a stiff tailwind.  When passing a tractor-trailer, one mile was often not quite enough to complete a passing maneuver.

[webny99]

I prefer having 2-mile signs in rural areas. Having a single 1-mile advance sign and a single sign at the exit is pretty sparse. You could miss the 1-mile sign while passing a truck and suddenly miss, or almost miss, your exit. Especially on a road like the Thruway where there's often 10-15 miles between exits, some redundancy to make sure drivers have plenty of warning is a good thing.

[Max Rockatansky]

A counter argument was not offered: if rural interstates shouldn't have mileage-based exits, what should the exit numbers be based off of?

There is probably a better argument for not having exit numbers at all out west versus going back to sequential numbers.

What do you mean "out west"? Plenty of rural spots in the east too, like the thirty-mile gap on the Mass Pike I mentioned earlier.

If I know I need to exit at Exit 300 and I'm at MM 258, I know I can assuredly pass a long string of trucks and have enough time to get in the right lane before my exit. But if I'm at MM 298, I might be better off hanging back and just driving slower since my exit is in only 2 miles. (Sure, there should be a 2-mile sign, but...well...New Mexico has interstates too.)

Since when has a two-mile sign been necessary? Say you're travelling at 70 mph; you still have almost a whole minute till the exit from the one-mile advance. I don't see the reason for a 2-mile sign, with one exception: major freeway-to-freeway junctions. These could have advances 10 miles back for all I care. But 2-mile advances build up anticipation of reaching the exit much more quickly than you actually will, and really there is plenty of time to move over to the right lane (which you should already be in unless you were passing someone) and make your exit from the one-mile advance sign.

This is one of the few instances in which New Mexico has done something correctly.

You have a lot more Delaware-like states out east where sequentially numbered exits can actually still be semi-effective.

[kphoger]

Illinois generally has 1-mile and ½-mile advance signage.  It wasn't till I drove in Kentucky that I saw 2-mile advance signage.  My preference would be 2-mile and ½-mile.

[SEWIGuy]

Two mile signage is also nice when there hasn't been an exit for awhile.  Otherwise 1 and 1/2 mile are fine.

[Amaury]

I've noticed Oregon also has more than just the "in 1 mile" signs. At least on the western side of the state. I've noticed a 1/2 mile, a 1/4 mile, etc. Washington has some, too, but not to the extent Oregon does.

[MultiMillionMiler]

A counter argument was not offered: if rural interstates shouldn't have mileage-based exits, what should the exit numbers be based off of?

The 1st exit: 1
The 2nd Exit: 2
The 3rd Exit: 3

And so on..

And no more N-S labeling, the same road in a different direction, should be a different Exit, especially if there are specific ramps you have to get on at the exit. At least with sequential numbering, you know once you reach the number just before the your exit, you know it's the next exit, whereas having exits 179, 214, 247, 267, 301..etc, you have no clue if your exit is coming up next unless you research ahead of time.

[US 89]

At least with sequential numbering, you know once you reach the number just before the your exit, you know it's the next exit

Ah, but it might not be. There might be a letter suffix exit in between that was added later on.

I get the sense you haven't done much driving out in the more rural regions of the US. Distance information is far more useful than knowing if your exit just happens to be the next one. Knowing how far away I am tells me if I need to move over and putter along behind a truck going 10 mph below the speed limit because my exit is coming right up, or if I can continue to comfortably pass slower traffic for the time being. Gaps of 10-20+ miles between exits are often the norm in less populated regions.

[CtrlAltDel]

Since when has a two-mile sign been necessary? Say you're travelling at 70 mph; you still have almost a whole minute till the exit from the one-mile advance.

You can put me in the camp of people who prefer a 2-mile sign when exit spacing permits, which incidentally, is what the MUTCD recommends:

For major and intermediate interchanges, Advance Guide signs should be placed at 1/2 mile and at 1 mile in advance of the exit with a third Advance Guide sign placed at 2 miles in advance of the exit if spacing permits. At minor interchanges, only one Advance Guide sign should be used. It should be located 1/2 to 1 mile from the exit gore. If the sign is located less than 1/2 mile from the exit, the distance displayed should be to the nearest 1/4 mile. Fractions of a mile, rather than decimals, should be displayed in all cases.

I would perhaps not make an exception for minor exits, though.

[Scott5114]

Regarding 2-mile signs: I don't expect them, but they sure are nice to have sometimes, much like ground-level repeater signals at intersections. And since I live in a state with 75 and 80 mph speed limits, having the extra mile worth of notice that your exit is coming up makes a lot of sense.

A counter argument was not offered: if rural interstates shouldn't have mileage-based exits, what should the exit numbers be based off of?

The 1st exit: 1
The 2nd Exit: 2
The 3rd Exit: 3

And so on..

And no more N-S labeling, the same road in a different direction, should be a different Exit, especially if there are specific ramps you have to get on at the exit. At least with sequential numbering, you know once you reach the number just before the your exit, you know it's the next exit, whereas having exits 179, 214, 247, 267, 301..etc, you have no clue if your exit is coming up next unless you research ahead of time.

That's how they used to sign exits in many states back when the Interstate system was first built.

It ended up breaking down pretty quickly due to the need to add new exits. (In one particularly stupid example, I-4 has a cloverleaf that at one point was signed as  Exit 53CA and Exit 53CB.) In most states that tried it, they threw in the towel and renumbered their exits to mile-based in the 1980s or so (and a second tranche of states did so around 2000).

As of the 2009 MUTCD, mile-based numbers are required nationwide.

[kphoger]

And no more N-S labeling

Do you mean no more cardinal direction auxiliary signs to accompany route shields at all?  That sounds less than useful.  If that's not what you mean, then what do you mean?

the same road in a different direction, should be a different Exit, especially if there are specific ramps you have to get on at the exit.

So, for example, if I-600 interchanges with US-1000, then that interchange might be Exit #17 in one direction but Exit #49 in the other direction?  That's an intriguing idea.  I keep trying to argue against it, but all my arguments seem weak.

At least with sequential numbering, you know once you reach the number just before the your exit, you know it's the next exit

As has already been mentioned, that isn't useful information in a lot of places.

For example, I-335 in Kansas only has a single exit between its endpoints.  If I'm driving north from Wichita to Topeka, and I get to the US-56 interchange, it's a lot more useful information to know that I'm 30 miles away from my exit than to know I'm only one interchange away.

Or if I'm starting to run low on gas during a road trip, and I see a billboard that says there's a truck stop at Exit #55, and I'm at Exit #47, and the exits are numbered sequentially, then I still have no clue how far it is to the truck stop.  Can I make it?  Who knows?  But if the exit numbers are mile-based, then I can easily tell that I'm just eight miles away.

whereas having exits 179, 214, 247, 267, 301..etc, you have no clue if your exit is coming up next unless you research ahead of time.

Which, again, doesn't really matter in rural areas.  It really only matters if the exits are close together.

[kirbykart]

And no more N-S labeling

Do you mean no more cardinal direction auxiliary signs to accompany route shields at all?  That sounds less than useful.  If that's not what you mean, then what do you mean?

the same road in a different direction, should be a different Exit, especially if there are specific ramps you have to get on at the exit.

So, for example, if I-600 interchanges with US-1000, then that interchange might be Exit #17 in one direction but Exit #49 in the other direction?  That's an intriguing idea.  I keep trying to argue against it, but all my arguments seem weak.

At least with sequential numbering, you know once you reach the number just before the your exit, you know it's the next exit

As has already been mentioned, that isn't useful information in a lot of places.

For example, I-335 in Kansas only has a single exit between its endpoints.  If I'm driving north from Wichita to Topeka, and I get to the US-56 interchange, it's a lot more useful information to know that I'm 30 miles away from my exit than to know I'm only one interchange away.

Or if I'm starting to run low on gas during a road trip, and I see a billboard that says there's a truck stop at Exit #55, and I'm at Exit #47, and the exits are numbered sequentially, then I still have no clue how far it is to the truck stop.  Can I make it?  Who knows?  But if the exit numbers are mile-based, then I can easily tell that I'm just eight miles away.

whereas having exits 179, 214, 247, 267, 301..etc, you have no clue if your exit is coming up next unless you research ahead of time.

Which, again, doesn't really matter in rural areas.  It really only matters if the exits are close together.

I think by N-S labeling MMM means the "I-80N" or "I-69E" sort of deal. Which doesn't really exist anymore, only in seven cases between two Interstates.

As for the different number exit thing, I think MMM is referring to a scenario such as this one:

Let's take an example of I-990 Exit 2 @ Sweet Home Road. Coming south on I-990, we have two exit ramps; one for going north on Sweet Home Rd, the other for going south. Currently these are Exits 2A-B; in MMM's ideal world they would be Exits 2 and 3.


I cannot believe that I-335 has only one exit between endpoints. That's crazy!

And yeah, MMM, the advance guide sign(s) shall give you plenty of notice for when your exit is coming. No need to know way ahead of time if your exit is next.

[Scott5114]

I cannot believe that I-335 has only one exit between endpoints. That's crazy!

Well, consider that the Kansas Turnpike was built as a New York Thruway-style toll road before the Interstate designations were assigned,, and the part that is I-335 now wasn't meant to be a standalone route.

[kirbykart]

I cannot believe that I-335 has only one exit between endpoints. That's crazy!

Well, consider that the Kansas Turnpike was built as a New York Thruway-style toll road before the Interstate designations were assigned,, and the part that is I-335 now wasn't meant to be a standalone route.

OK, that makes sense.

[vdeane]

I'm pretty sure MMM mean stuff like this when he's talking about N-S labeling.