Sequential exit numbering & conversion to milepost exit numbering

[deathtopumpkins]

Unlike most people in this thread, I like sequential numbering and hate distance-based numbering.  I find it too difficult to figure out the distance between exits in my head.  The only time I do like distance-based numbering is when I'm going through an entire state heading west or south.  It tells me the remaining distance on the road in that state.

Fortunately for me, New York has sequential numbering! :partyhat:

I agree, I like sequential exit numbering as well....most motorists don't notice mileage in my opinion.  But, they do expect exit 2 to be before exit 3.  I don't understand what is wrong with sequential numbering...it seems like common sense to me.

Well what's wrong with it is the fact that if you add in an exit between 2 and 3, what do you number it? 2A makes it seem related to exit 2, especially if 2 already has an A and B so it's given C. Thus if you didn't want to deal with this issue, you would end up having to renumber all the exits after it on the freeway, which would be very costly.
And distance-based also has the added benefit of making it easier to determine how far away your exit is. For instance, you are getting off at exit 267, and see that you are at milepost 193. Thus you have about 74 miles left until your exit.

[roadfro]

I agree, I like sequential exit numbering as well....most motorists don't notice mileage in my opinion.  But, they do expect exit 2 to be before exit 3.  I don't understand what is wrong with sequential numbering...it seems like common sense to me.

Motorists do expect exit 2 to be before exit 3...unless they're going the other direction 


Where sequential exit numbering seems to make less sense is when exits are greatly spaced.  It seems like it might be weird to have an exit 10 be twenty miles from exit 11.  And then, what do you do when a new exit is added in between?  Adding a new interchange is where mileage-based numbering wins out, because you may only have to add letters to existing signs to accommodate a new ramp, whereas sequential numbering may require renumbering a significant stretch of the highway (unless multiple letters are used or interchanges can be numbered/lettered out of sequence).

There are some points where sequential numbering makes a bit more sense.  While Nevada uses milepost-based exit numbers, this principle is slightly disregarded in the Reno-Sparks area on I-80. All exits from US 395 (exit 15) east to Vista Blvd (exit 21) do not fall in their actual milepost zone, due to many interchanges being spaced closer than one mile apart.  The seven exits in this range are actually numbered sequentially, in an apparent effort to avoid using lettered exits for unrelated interchanges.  The result is that exit 21 ends up being about three miles from exit 22 (which is outside the Reno-Sparks urban area).

[froggie]

I agree, I like sequential exit numbering as well....most motorists don't notice mileage in my opinion.

For commuter-style travel, typically not.  But for distance travel, yes they do notice.

[Scott5114]

If you live in a state with milepost exit numbering, you can be the life of the party for a few brief moments by explaining "the trick" to exit numbers to people that don't know it. "Hey, did you know that you can find out how far away from..."

Girls may or may not think it's pretty nifty. In any event you could formulate some ludicrous pick-up lines from it!

[hbelkins]

I agree, I like sequential exit numbering as well....most motorists don't notice mileage in my opinion.  But, they do expect exit 2 to be before exit 3.  I don't understand what is wrong with sequential numbering...it seems like common sense to me.

Oh, I notice mileage. If I know the milepost where I am at and the exit number I'll be using to leave the freeway/interstate/expressway, I can do the math in my head and figure out how long it'll take, if I need to stop for gas before my exit, etc.

[Michael]

Unlike most people in this thread, I like sequential numbering and hate distance-based numbering.  I find it too difficult to figure out the distance between exits in my head.  The only time I do like distance-based numbering is when I'm going through an entire state heading west or south.  It tells me the remaining distance on the road in that state.

Fortunately for me, New York has sequential numbering! :partyhat:

I agree, I like sequential exit numbering as well....most motorists don't notice mileage in my opinion.  But, they do expect exit 2 to be before exit 3.  I don't understand what is wrong with sequential numbering...it seems like common sense to me.

Well what's wrong with it is the fact that if you add in an exit between 2 and 3, what do you number it? 2A makes it seem related to exit 2, especially if 2 already has an A and B so it's given C. Thus if you didn't want to deal with this issue, you would end up having to renumber all the exits after it on the freeway, which would be very costly.
And distance-based also has the added benefit of making it easier to determine how far away your exit is. For instance, you are getting off at exit 267, and see that you are at milepost 193. Thus you have about 74 miles left until your exit.

In Central New York, we letter related exits "N/S" or "E/W" (cardinal directions, duh!).  A suffixed "A", "B", etc. is an exit added after the initial numbering.  I'm not sure if the rest of the state does the same.

[english si]

Where sequential exit numbering seems to make less sense is when exits are greatly spaced.  It seems like it might be weird to have an exit 10 be twenty miles from exit 11.  And then, what do you do when a new exit is added in between?

you call the new exit 10a? Personally I think mileage-based exits fall down when distances between exits are bigger (eg France, UK rural motorways and very rural US ones) - I can imagine it being more confusing to have the junctions go 49, 56, 61 or whatever than 7, 8, 9. After all, you've just passed exit 23 - how many exits is it to your one, 38? The nice sign tells you that you are 17 miles from your destination, but you're going to have to read signs for that junction number, rather than glance at them and count upwards so you know it's the right junction. Sequential over big stretches would be frustrating rather than confusing "come on, where's this exit, it must be soon" kind-of-thing.

Adding a new interchange is where mileage-based numbering wins out, because you may only have to add letters to existing signs to accommodate a new ramp, whereas sequential numbering may require renumbering a significant stretch of the highway (unless multiple letters are used or interchanges can be numbered/lettered out of sequence).

I think you'd find it's the multiple letters (nothing higher than b in the UK - and that only a handful of times - 3 times on motorways and 4 times on A roads). In Glasgow, Scotland, the M74 is being extended to the M8. Which is fine, except it starts at junction 1 and will have three junctions before that. I don't think kmposts are changing (though junction 1 is km 0, so I have no idea what they are doing for them - I'd guess they'd just consider the M74 as slips off the M8 until the current j1) - a mileage/kmage based system would have to renumber the whole road (itself not a bad thing). However what they are going to do is have 1, 1a, 2, 2a (currently 1), 3 (currently 2), 3a (currently 3) and 4 (currently 4) - just 3 renumbered junctions, rather than 13.

Also in Glasgow, the M8 has a few junctions in close succession, but rather than having 24, 24a, 24b, 24c (no idea on actual exit numbers under a mileage-based system) there's no letter suffixes, but unique numbers. You touch on sequential's benefit here, where junctions are close with your Reno example.

There's pluses and minuses with both systems and I'm on the fence over what one is better.

[TheStranger]

roadfro: I've always been of the mind that it really depends on what type of road - the New Jersey Turnpike really goes well with sequential numbering IMO, for instance, but I think in most instances mile-based is more practical.

[J N Winkler]

Personally I think mileage-based exits fall down when distances between exits are bigger (eg France, UK rural motorways and very rural US ones) - I can imagine it being more confusing to have the junctions go 49, 56, 61 or whatever than 7, 8, 9. After all, you've just passed exit 23 - how many exits is it to your one, 38? The nice sign tells you that you are 17 miles from your destination, but you're going to have to read signs for that junction number, rather than glance at them and count upwards so you know it's the right junction. Sequential over big stretches would be frustrating rather than confusing "come on, where's this exit, it must be soon" kind-of-thing.

It is true that with mileage-based systems, you lose the benefit of having an easy-to-remember sequential number which you can count up or down from your entry point.  But as a generalization, even in rural stretches with widely spaced interchanges, I would expect the majority of drivers to find it more useful to be able to estimate the time until they reach their exit, using a system of exit numbering which is easily related to the distance indications on mileposts.

I can't speak for British drivers who have grown up with sequential junction numbering, but as an American growing up with mileage-based numbering, I can say that I never bother to count the exits between my current location and the exit I need to take.  Americans tend to assume that wherever a major road (generally a paved road in thinly populated rural areas) crosses the freeway, an exit will be provided.  Mileage-based numbering allows them to ignore the particularities of intersecting road development on the intervening length of freeway, which often includes new exits put in on a fairly regular basis to cater for outlet malls and suchlike commercial development.  (Britain has much less of this sort of development in general, and very little of it results in new interchanges even on grade-separated all-purpose roads, because the planning system is highly restrictive and leads to land development costs which are up to ten times those encountered in the US.)

Another factor which affects counting is that in Britain sign designers have the option of showing the junction number on an entry slip, while Americans rarely if ever show exit numbers on entry ramps.  In Britain you are sometimes told you are entering at Junction 5; in the US you are never told you are entering at Exit 445A.

Adding a new interchange is where mileage-based numbering wins out, because you may only have to add letters to existing signs to accommodate a new ramp, whereas sequential numbering may require renumbering a significant stretch of the highway (unless multiple letters are used or interchanges can be numbered/lettered out of sequence).

I think you'd find it's the multiple letters (nothing higher than b in the UK - and that only a handful of times - 3 times on motorways and 4 times on A roads). In Glasgow, Scotland, the M74 is being extended to the M8. Which is fine, except it starts at junction 1 and will have three junctions before that. I don't think kmposts are changing (though junction 1 is km 0, so I have no idea what they are doing for them - I'd guess they'd just consider the M74 as slips off the M8 until the current j1) - a mileage/kmage based system would have to renumber the whole road (itself not a bad thing). However what they are going to do is have 1, 1a, 2, 2a (currently 1), 3 (currently 2), 3a (currently 3) and 4 (currently 4) - just 3 renumbered junctions, rather than 13.

There is not much difference between sequential and distance-based numbering systems from this standpoint.  A certain amount of massaging is possible (and indeed routinely done) with both.  California has freeways where the exit numbering is based on non-traversable routings between a projected ultimate terminus and the start of the actual length of traffickable road.  Before Utah DOT resurveyed I-15 on a consistent baseline and changed exit numbers accordingly a few years ago, differences in length between the projected and actual alignments of I-15 were dealt with by stretching or compressing (as required) the distances between numbered exits in relation to the actual mileages.

Although one of the touted advantages of mileage-based exits is a transparent indication of distance to exit, this is inevitably approximative, as is mileposting in general unless mileage equations are explicitly indicated.  Mileage-based exit numbering, when used with mileposts, is generally good enough to let you know within, say, five minutes how far it is to your desired exit, but it is not good enough to check your speedometer.  This is why states with mileage-based exit numbering and mileposts still have surveyed speedometer check sections, and also why I confine my own speedometer check exercises to lengths of the Kansas Turnpike which have not been touched since 1956.

Also in Glasgow, the M8 has a few junctions in close succession, but rather than having 24, 24a, 24b, 24c (no idea on actual exit numbers under a mileage-based system) there's no letter suffixes, but unique numbers. You touch on sequential's benefit here, where junctions are close with your Reno example.

To be fair, in the absence of explicit mileposting in California (county-based mileposting is still all there is right now), there is little to choose between sequential and distance-based systems in that state.  There are urban freeways with closely spaced exits (think downtown LA freeway ring) where sequential numbering inevitably has an advantage.  Plus, in the absence of explicit mileposts referred to the same starting point as the exit numbers, and without knowing how long the freeway is in each county through which it passes, it is not possible to know the distance to the desired exit until you pass an intermediate exit.  This can take a very long time in the California desert--think I-10 in eastern Riverside County.

There's pluses and minuses with both systems and I'm on the fence over what one is better.

I'm mileage-based all the way!

[vdeane]

In Central New York, we letter related exits "N/S" or "E/W" (cardinal directions, duh!).  A suffixed "A", "B", etc. is an exit added after the initial numbering.  I'm not sure if the rest of the state does the same.

I believe the rest of the state uses A/B (except Northern NY and the Southern Tier).  Since about a year or two ago, central NY has actually been in error in doing that, ever since the adeoption of the federal MUTCD.

[Duke87]

In Central New York, we letter related exits "N/S" or "E/W" (cardinal directions, duh!).  A suffixed "A", "B", etc. is an exit added after the initial numbering.  I'm not sure if the rest of the state does the same.

I believe the rest of the state uses A/B (except Northern NY and the Southern Tier).  Since about a year or two ago, central NY has actually been in error in doing that, ever since the adeoption of the federal MUTCD.

Southern NY is generally directional as well, although there are exceptions. I-95 has exits 18A-B for Mamaroneck Avenue. The Henry Hudson Parkway has 23A-B for Broadway/US 9.

[shadyjay]

After Maine converted to mileage-based exits, I thought for sure that NH and VT would follow suit.  I emailed VTrans and they said (back in 2005) that they had no plans to convert to mile-based exits.  Figures... it would be the easiest state to do it in, as not a single interstate exit has been added since the interstate system was constructed, and 95% of the exits are more than 2 miles apart, with some being 10-15 miles apart. 

Converting in CT would be confusing to some, since especially on I-95 between New York and New Haven, there are 50 exits in 50 miles, so you may have exits only changed by 1 or so.  I would number them so that you wouldn't have A and B exits, whenever possible.  If a couple exits are a mile or so off, no big deal.  I-84 through Hartford would be more challenging, but that could be solved by closing/consolidating some exits.  I-395 would benefit the most as its exits start at "77", though if it was up to me, a mile-based system would continue I-95's exits on I-395, harking back to the turnpike days. 

Any changes to the New Jersey Turnpike exits should have the lowest exit at the south end and the highest exit at the GWB, and not convert to I-95 mileage halfway up.  The Thruway would be a bit more challenging, but I'd still have Exit 1 be where the Thruway begins, and have I-90 remain "backwards numbered". 

[Scott5114]

It's good to have a UK perspective upon this, as they have an entire freeway network with sequential junctions, and so can provide insight we might not be able to have based on its limited application in the U.S.

Can anyone inform me upon whether the UK uses milemarker/kmarker signs posted along the motorways? This is one of the major niceties that aids mileage-based systems the most. Even if there is no Exit 223, there will still be a marker informing you that you are at Mile 223, and if you're planning on getting off at 243, you still have 20 miles to go, and will be reminded of where you are at one-mile intervals. Missouri even goes through the extra effort of putting markers every fifth of a mile, complete with small reassurance markers, so you will be reminded you are on I-44 East at 72.0, 72.2, 72.4, 72.6, 72.8, as well as at 73.0 (and so on).

I used to reduce my cruise control by three MPH–setting it at exactly 72 MPH–upon entering Missouri, so that I would be at my exit in Springfield in exactly one hour!

[J N Winkler]

Can anyone inform me upon whether the UK uses milemarker/kmarker signs posted along the motorways?

Britain (not sure about NI) has km-posting of sorts.  The signs in question are called "driver location signs" and are similar in function to the enhanced location reference markers you see on freeways in a number of US cities.  But they are not well-formatted for navigational purposes.  The standard design (used both on motorways and all-purpose roads) has blue background, yellow (!) legend, and white border, and formats the information like this:

M6
A
193.7

where "M6" is the road number, "A" is a carriageway designator (A = going away from London, B = going towards London, and there are other designators as well, designed e.g. for use with slip roads within interchanges), and "193.7" is the distance in km from a designated datum point which may be, but often is not, the start of the route.

Further information can be found in the Highways Agency's Interim Advice Note on driver location signs:

http://www.standardsforhighways.co.uk/ians/pdfs/ian93.pdf

Before driver location signs were introduced, motorways and certain important A-roads had flexible roadside posts giving the distance in km and tenths from a given datum point, as well as an arrow pointing to the nearest emergency telephone.  But the legend on these posts was much smaller than on the current driver location signs.

[Duke87]

Evidence that I am an utter egghead, file #37601:

So, yesterday, when I was bored, I came up with a formula for calculating the relative benefit of switching to milepost numbering on a highway by highway basis.


Some calculated values of F_B with this formula....

I-84, NY: 7.01
I-84, CT: 3.01
I-84, MA: 0.31
I-87, NY: 169.19
I-90, NY: 739.14
I-90, MA: 22.96
I-91, CT: 1.72
I-91. MA: 1.60
I-91, VT: 18.92
I-95, NY: 0.38 (0.015L=0.35)
I-95, CT: 3.78
I-95, RI: 2.16
I-95, MA: 2.94
I-95, NH: 1.29

The very large values for I-87 and I-90 in New York are, of course, due to the Thruway making the numbers start over and run backwards. Were they sequentially numbered properly F_B would be considerably lower.
No highway I've looked at so far in Connecticut or Rhode Island produces a value of F_B>5. In Massachusetts, only I-90 and I-495 do (Well, MA-2 probably would as well if I had milepost data for it...). In New Hampshire, only I-93 and NH-101 do. Meanwhile, in Vermont, Both I-89 and I-91 do; and in New York, every primary interstate except for I-95 does.


So there you go. Take all that for whatever subjective worth you wish...

[agentsteel53]

I think I like mileposts for consistency, and suffix letters in densely packed areas are fine by me.  Hell, look at Kansas City, with its Exit 2 complex.  The numbering (lettering) of the exits is the least of their problems.

[mightyace]

The [mu] and [m] variables are the same thing, is one of them supposed to be median? 

[agentsteel53]

Evidence that I am an utter egghead, file #37601:

So, yesterday, when I was bored, I came up with a formula for calculating the relative benefit of switching to milepost numbering on a highway by highway basis.
[some large image] ....

a real egghead would use LaTeX to write up those formulae!

[Scott5114]

Evidence that I am an utter egghead, file #37601:

So, yesterday, when I was bored, I came up with a formula for calculating the relative benefit of switching to milepost numbering on a highway by highway basis.
[some large image] ....

a real egghead would use LaTeX to write up those formulae!

An even bigger egghead would then refer to it as L^AT_EX!

[roadfro]

To be fair, in the absence of explicit mileposting in California (county-based mileposting is still all there is right now), there is little to choose between sequential and distance-based systems in that state.  There are urban freeways with closely spaced exits (think downtown LA freeway ring) where sequential numbering inevitably has an advantage.  Plus, in the absence of explicit mileposts referred to the same starting point as the exit numbers, and without knowing how long the freeway is in each county through which it passes, it is not possible to know the distance to the desired exit until you pass an intermediate exit.  This can take a very long time in the California desert--think I-10 in eastern Riverside County.

It's true that California doesn't use statewide mileposts. However, according to the Cal-NExUS site, their exit numbers are posted based on statewide mileage. Thus, one *can* generally use exit numbers to estimate mileage on California Freeways. In California's case, estimating distance by exit number is far more convenient than relying on a postmile panel.

Nevada DOT follows a milepost/exit number policy similar to that of Caltrans.  This is particularly evident in the case of US 395.  All exits on freeway portions of US 395 in Reno and Carson City are based on the statewide mileage, despite the fact that the county mileage is smaller.  This is also done on I-80 (although in this case, the interstate uses MUTCD-style mileposts with statewide mileage in addition to the Nevada-style mileposts indicating county mileage at bridges/interchanges).

[J N Winkler]

It's true that California doesn't use statewide mileposts. However, according to the Cal-NExUS site, their exit numbers are posted based on statewide mileage. Thus, one *can* generally use exit numbers to estimate mileage on California Freeways. In California's case, estimating distance by exit number is far more convenient than relying on a postmile panel.

This is true.  The point I was actually trying to make is that in order to orient yourself in relation to the exit you want, you must first pass a numbered exit.  In the desert, where exits are widely spaced (something like 10-20 miles), that can entail a significant amount of driving time.

To give an example, suppose I enter I-10 at Ford Dry Lake Rd. (Exit 217) going west.  I won't know how far I am from, say, the I-405 stack interchange until I pass the next exit (Exit 201), 16 miles and about 14 minutes later.  In contradistinction, if mileposts were provided in addition to (or instead of) the postmiles, I would know the distance in less than a minute.

[agentsteel53]

add to that that Ford Dry Lake Road is about a half-mile long and leads to Chuckwalla Valley Road, which is the road most people intend to take, but is not labeled on any sign.  Yep, I've missed that exit because I had no idea that "exit 219" on the map was that unlabeled exit in the field, which is oh-so-informatively located about 117 miles from the Riverside County line. 

And then I had to drive 17 miles east to the next exit (the other end of Chuckwalla Valley Road). 

California postmiles - dumb as Hell.

[J N Winkler]

The very first time I drove in California, I crossed the Colorado River on I-10 in December 1998, bound for Los Angeles.  My thought process was as follows:

*  Why did that exit not have a number?

*  Why are there no mileposts?

*  What do those little white things at the side of the road mean?

*  Why does every little white thing have "RIV" at the top?

Eventually, around RIV-10-110.3, I figured out that these "little white things" were mile markers of some description.  Like many people who had never actually visited LA, let alone driven in its basin, I had a sort of mental map where Riverside County ended, umm, about five blocks east of the Pacific Ocean.

*  Ah!  (RIV-10-100.5)  I am about 100 miles from LA.

[agentsteel53]

yeah, I wonder who decided to use county-based postmiles in the 1920s when they were first put up.  Other states had mileposts that were zeroed at the state line or route terminus, why not CA?  A lot of things CA did were brilliant (red stop signs, etc) but this idea was asinine.

[Brandon]

yeah, I wonder who decided to use county-based postmiles in the 1920s when they were first put up.  Other states had mileposts that were zeroed at the state line or route terminus, why not CA?  A lot of things CA did were brilliant (red stop signs, etc) but this idea was asinine.

It's not unusual on non-interstates.  Illinois uses a county based mileposting system for state and US routes.  It's a green cricle with the following inside:
{route number - black on white}
{county - white on green bar}
{mileage - black on white}

Thus:

83
DUPAGE
8

I can't seem to find a photo of one online.