Why don't European highway systems use shields a kin North American systems?

[NE2]

Err, that picture says nothing - NORTH 695 TO NORTH 95 - not what I was talking about with different directions.

It could just as easily be EAST 695 TO NORTH 95.

[deathtopumpkins]

Which helps my point. If you're going to consistently use "The SOUTH", "The EAST", etc. as a destination, why not just include the cardinal directions all the time.

1)Because we neither have the road geography that provides each road with a simple pair of opposite cardinal directions - a few more could be done N-E or something - but most can't - trust me.
2)Because that's not how we work - numbers and destinations - the Regional Destinations are mostly for the Trunk road network - there's times where the cardinal direction (or The MIDLANDS, or the four secondary compass point - though London replaces the south east, or NORTH WALES, MID WALES and SOUTH WALES, or SCOTLAND) work better than giving a few cities, but not every time - or we'd use them more often.
3)We don't long distance traffic not on the long-distance network.
4)We want The WEST or The NORTH, or whatever on a beltway, as a destination, when it's not the direction.
5)We have nowhere to put it on signs - we fairly frequently have some direction indicator other than destination, but proper directions don't really fit.
6)It'll look ugly without a radical overhaul of the UK sign system.

I feel like it would be easier to have signs say "M6 SOUTH" rather than just list "the South" as if it were a destination.

Given that there's nowhere to put a direction, listing it as a destination works well. And it is a destination - more than just a direction - signs to The SOUTH dry up when you are there.

As I've alluded to, not everything that works in America works everywhere else. There's more than one way to skin a cat.

I never once said that you guys were doing it the 'wrong way'. Though using the argument "that's how we do it" to justify something is NOT good enough. I don't understand why people from other parts of the world aren't allowed to question the European system at all. I do not think it's wrong, and I never said it was wrong. I merely presented a flaw with the system, yet here you are attacking me because "not everything that works in America works everywhere else".

Also, you certainly do have room to put it on signs though. 4 (or 5) letters do not take up that much space. It would easily and attractively fit right next to the "M5" on that sign you used as an example.



And NE2 is right, the method depicted on that sign from I-70 in Baltimore does indicate which directions can be accessed from it. "I-695 EAST TO I-95 NORTH" means the same thing as "695 to The North".

Finally:

As I've said - more than one way to skin a cat. The American way works, the German way works, our hybrid between the two works - as it ain't broke, don't fix it.

I'm not saying that it's broke[n] and needs to be fixed, but surely you must recognize that all systems have their flaws, and the British system's flaw was pointed out previously. I just think that people shouldn't be attacked for pointing that out.

[vdeane]

I can't understand how someone could navigate without using route numbers and directions, so Europeans signage is always impossible for me to decipher.

[english si]

Though using the argument "that's how we do it" to justify something is NOT good enough.

I gave several reasons, you ignore them - it's actually more the American system that's been justified as "that's how we do it", though of course, it's the status quo for most people here.

Also, you certainly do have room to put it on signs though. 4 (or 5) letters do not take up that much space. It would easily and attractively fit right next to the "M5" on that sign you used as an example.

Not really - especially not without undermining the central location of the route number - which is more important than the direction you are going. You've not given a reason why Brits should sign directions like the Americans other than "that's how we do it, here in America" - you've already said that "that's how we do it" is a poor argument, yet that is pretty much your argument here.

I'm not saying that it's broke[n] and needs to be fixed, but surely you must recognize that all systems have their flaws, and the British system's flaw was pointed out previously. I just think that people shouldn't be attacked for pointing that out.

You are saying it's broken - you want a radical overhaul from destinations to directions. I'm saying that that would break it more - that it's not a flaw, but an idiosyncratic feature of our road network and road history. You were the first to bring up this 'flaw' with the British system (other than my discussion of previous discussion with continental Europeans, when he had the opposite problem - that we use 'South' etc too much) - others brung up flaws with the American system (and got attacked for it) or the Continental system - the British system is different (though perhaps you made the Canada is the same as the USA type-fallacy?)

If there is a flaw in the British system, it's more that we don't cater well enough for the European travellers, not that we don't confuse the majority of visitors even more by using a system that is totally incomprehensible to them to please a handful of Americans who drive here - after all "People want to go to places and not in a certain direction. Hence it is irrelevant which direction it really is." and "it is mainly based on road numbers. And that's the reason why this sign is utter crap."

It could just as easily be EAST 695 TO NORTH 95.

Yes that was obvious, but you gave a bad example, so I wasn't sure if you had gotten what I was saying. Still a very large sign and confusing to continentals, therefore totally unsuitable for the UK.

I can't understand how someone could navigate without using route numbers and directions, so Europeans signage is always impossible for me to decipher.

And Firefly has the opposite problem, which is why debates over the better system are silly and why people from a different system don't understand how the system works. This leads to 'improvements' being suggested which are basically "follow my system" - like this idea that regional destinations in the UK should be cardinal directions (USA 'improvements') or scrapped and replaced with some arbitrarily chosen control destination that's fairly large and quite a way along the road if not all the way (European 'improvements').

[Brandon]

Most European countries use a colour code to distinguish different types of roads. That makes the use of flamboyant shields dispensable.

Finland has a nice assortment of colors (this could almost go in the "Sine Salad" thread):

International arterial highway, or "E" route (always multiplexed with a national highway route in Finland, example below): 


National highways:


Highway 7/E18 (most of E18 is being upgraded to motorway standard (much of it already is), and when that happens, the blue background becomes green):


Regional highway:


Local (secondary) highway:


"Other" local (secondary) highway:

These work fine, unless, of course, you're colorblind.  Is there someone here who is either completely colorblind or red-green colorblind to tell us what they see?

[deathtopumpkins]

english si, I have given several reasons. As I keep saying, "that's how we do it" is never an acceptable reason, and as you'll see if you could get past the fact that I'm an American for long enough to read my post, I never once used that as a reason.

I gave you scenarios in which having the direction would be helpful, and situations in which you cannot easily navigate by destination alone. You merely ignored those parts of my posts and attacked me for questioning the European system. You never, ever reply to the parts of my post that present any reasoning or example. You merely complain over and over again about how I want to destroy the sanctity of British roads.

I also never said you guys were doing it wrong and needed to change. And I was certainly not the FIRST to question this. I never even replied to this thread until the bottom of the second page! I don't understand where this tremendous amount of animosity and accusations are coming from!

I am not telling Europe to do it the American way, and I think before you reply to this thread again you need to re-read it, so you can stop accusing me of things I have not done and consider maybe using a little logic in the discussion, as well as consider and respond to the logic we have presented, rather than just attacking people for questioning anything.

Oh and,

(though perhaps you made the Canada is the same as the USA type-fallacy?)

what the hell are you talking about?

[firefly]

For example, say I'm getting on I-95 in Westchester County, NY (just outside NYC). If I got on northbound, I could be heading to Portland or Portsmouth or Boston or Providence or New London or New Haven, all by staying on I-95, and all within 6 hours of driving. Other destinations of note that I could be headed for include Cape Cod, Fall River, or New Bedford (via I-195), Plymouth (via US 44), Hartford or Springfield (via I-91), Worcester (via I-395), or any of dozens of other sizable cities in New England. But to get to ALL of these places I know that when I get on I-95 I need to head north. If the signage lacked the direction north, I would instead need to know that I need to head toward New Haven, then pick a new destination there. But if I'm a tourist who is completely unfamiliar with relatively minor Connecticut cities (like New Haven), headed from a NYC airport up to Boston, I will know that Boston is north[east] of New York, but probably not where New Haven is or where to go from there.

Destinations are categorised by their prominence which reflects their size and their importance as a traffic hub. In this case it isn't particularly difficult to determine Boston as the prime destination on the I-95 which ought to be signposted from the junction with I-78 on.
Additional to the prime destination there can also be intermediate destinations with less but still significant prominence. These secondary destinations are not signposted before the preceding secondary destinations has made way. So that the number of destinations never exceed 4 per direction.

The first junction after leaving NYC could look like this:

If you wonder what Central New Rochelle is. That is the name I picked for the following junction.

I admit that my quick survey of the geography in southern New England might not be too profound. And the pick of some destinations at the expense of others is debatable.

In short, there are too many intermediate destinations for you to follow your destination the whole way even for day trip distances. You need to know intermediate destinations. Whereas with cardinal directions you can follow that the whole way.

One follows one prime destination for a long distance in most cases. The changing intermediate destinations can then be ignored.

[Scott5114]

Looking at that Google Maps link that was posted...The NORTH, The WEST, The SOUTH... so the M3 will take me anywhere as long as it's not in the east? Neat.

I'm glad that we don't have this convention in the US... I-85 and I-95 will both certainly take you to "The SOUTH", but they go to very different places.

[mcdonaat]

Most European countries use a colour code to distinguish different types of roads. That makes the use of flamboyant shields dispensable.

Finland has a nice assortment of colors (this could almost go in the "Sine Salad" thread):

International arterial highway, or "E" route (always multiplexed with a national highway route in Finland, example below): 


National highways:


Highway 7/E18 (most of E18 is being upgraded to motorway standard (much of it already is), and when that happens, the blue background becomes green):


Regional highway:


Local (secondary) highway:


"Other" local (secondary) highway:

These work fine, unless, of course, you're colorblind.  Is there someone here who is either completely colorblind or red-green colorblind to tell us what they see?

Ah yes, I see Green, Red, Purple, Green, White, Purple. Dunno if those are the right colors...

[Brandon]

These work fine, unless, of course, you're colorblind.  Is there someone here who is either completely colorblind or red-green colorblind to tell us what they see?

Ah yes, I see Green, Red, Purple, Green, White, Purple. Dunno if those are the right colors...

Thanks, mcdonaat.

They're green, red, blue (with red and green), yellow, white, and blue.  However, it makes my point about these being a poor signage choice for the colorblind.  If the green sign and the yellow sign are the same number, and put next to each other, it is impossible for someone such as macdonaat to tell the difference between the route.  This is where shields are far superior to differing colors.

[Scott5114]

For example, say I'm getting on I-95 in Westchester County, NY (just outside NYC). If I got on northbound, I could be heading to Portland or Portsmouth or Boston or Providence or New London or New Haven, all by staying on I-95, and all within 6 hours of driving. Other destinations of note that I could be headed for include Cape Cod, Fall River, or New Bedford (via I-195), Plymouth (via US 44), Hartford or Springfield (via I-91), Worcester (via I-395), or any of dozens of other sizable cities in New England. But to get to ALL of these places I know that when I get on I-95 I need to head north. If the signage lacked the direction north, I would instead need to know that I need to head toward New Haven, then pick a new destination there. But if I'm a tourist who is completely unfamiliar with relatively minor Connecticut cities (like New Haven), headed from a NYC airport up to Boston, I will know that Boston is north[east] of New York, but probably not where New Haven is or where to go from there.

Destinations are categorised by their prominence which reflects their size and their importance as a traffic hub. In this case it isn't particularly difficult to determine Boston as the prime destination on the I-95 which ought to be signposted from the junction with I-78 on.
Additional to the prime destination there can also be intermediate destinations with less but still significant prominence. These secondary destinations are not signposted before the preceding secondary destinations has made way. So that the number of destinations never exceed 4 per direction.

The first junction after leaving NYC could look like this:

If you wonder what Central New Rochelle is. That is the name I picked for the following junction.

I admit that my quick survey of the geography in southern New England might not be too profound. And the pick of some destinations at the expense of others is debatable.

In short, there are too many intermediate destinations for you to follow your destination the whole way even for day trip distances. You need to know intermediate destinations. Whereas with cardinal directions you can follow that the whole way.

One follows one prime destination for a long distance in most cases. The changing intermediate destinations can then be ignored.

This is actually not all that different than what is done on the freeways in the US. You have a "control city", which is supposed to be the 'prime destination'. Unfortunately it can break down sometimes since each state is more or less free to select whatever city it feels is appropriate. Oklahoma does a good job by showing the north-south destinations from Oklahoma City as Wichita and Dallas, but some states can be pretty bad at it, like Pennsylvania and Colorado (raise your hand if you've heard of Limon!) In the case of I-95 as shown here, I believe the next city shown north of NYC is New Haven, then Hartford, then Providence, then Boston.

Interchanges normally usually don't have "names" here...once you enter a city, like New Rochelle, you see a sign that says "New Rochelle: Next 2 Exits" and then it's not shown anymore. However, large cities sometimes do sometimes include the city centre/downtown area as a destination.

These work fine, unless, of course, you're colorblind.  Is there someone here who is either completely colorblind or red-green colorblind to tell us what they see?

Ah yes, I see Green, Red, Purple, Green, White, Purple. Dunno if those are the right colors...

The background of the 7/E18 and 3622 are blue. The 42 is yellow.

[realjd]

Looking at that Google Maps link that was posted...The NORTH, The WEST, The SOUTH... so the M3 will take me anywhere as long as it's not in the east? Neat.

I'm glad that we don't have this convention in the US... I-85 and I-95 will both certainly take you to "The SOUTH", but they go to very different places.

Keep in mind that the total land area of Great Britain is smaller than many US states. A better example would be if California signed regions like "The South", "The Desert", "The Central Valley" which would work just fine.

[vdeane]

People like to compare European countries to US states, but the size difference isn't that extreme.  The only state (other than Alaska) that approaches the size of countries like France or Germany is Texas.

[Chris]

Control cities in the United States appear to be somewhat different from Europe. In Germany and France, you can navigate the entire country via just 3 to 4 control cities. For instance, on I-70 eastbound at Denver, Kansas City would've been the control city if it was in Europe. Places like Limon or Hays would not be control cities in Europe, at least not primary control cities.

Also note that in countries like Germany, UK, France, Spain or Italy the freeway network is much denser than even most of eastern United States. If there's more than 60 - 80 miles between parallel freeways, it's huge. The population density is higher, there are more medium/large cities and more importantly, not all countries operate a grid-like freeway network, making cardinal directions less useful than they are in the U.S.

[Duke87]

In the case of I-95 as shown here, I believe the next city shown north of NYC is New Haven, then Hartford, then Providence, then Boston.

Actually, it's New Haven (or, on recent NYSDOT signage, "New Haven CT"), New London, Providence, then Boston. Hartford would be a significant destination from this point, but it is not along I-95. In the US, control cities not directly along the highway in question are usually not used unless said highway ends before you get there or there is no prominent control point along said highway within reasonable distance.

Interchanges normally usually don't have "names" here...once you enter a city, like New Rochelle, you see a sign that says "New Rochelle: Next 2 Exits" and then it's not shown anymore. However, large cities sometimes do sometimes include the city centre/downtown area as a destination.

Indeed. I also note that the mockup here lacks an exit number (should be 15) - exit numbers are very prominent in freeway navigation in the US and you change the game a lot if you start omitting them. "Exit 16" is more meaningful to your average motorist on I-95 than "Central New Rochelle" (which, by the way, could also be a destination from exit 15)

[cpzilliacus]

These work fine, unless, of course, you're colorblind.  Is there someone here who is either completely colorblind or red-green colorblind to tell us what they see?

A few things:

• Finland generally does not repeat route numbers;
• European route numbers always have an "E" prefix (as in many other EU nations) and are always green;
• National highways are always numbered 1 to 29 (and use red, which does not usually get mixed up with blue and green);
• Regional highways are always numbered 40 to 99;
• Secondary highways are numbered 100 to 999; and
• "Other" or municipal highways are numbed 1,000 and above.

[Scott5114]

In the case of I-95 as shown here, I believe the next city shown north of NYC is New Haven, then Hartford, then Providence, then Boston.

Actually, it's New Haven (or, on recent NYSDOT signage, "New Haven CT"), New London, Providence, then Boston. Hartford would be a significant destination from this point, but it is not along I-95. In the US, control cities not directly along the highway in question are usually not used unless said highway ends before you get there or there is no prominent control point along said highway within reasonable distance.

Blargh. My Connecticut geography is extremely hazy.

[Sykotyk]

European style seems to imply you ONLY take the freeway between major points, and your basis of travel is getting to that freeway as quickly as possible.

If I'm driving from Tucson AZ to Cincinnati OH, this is how I do it in the US:

I-10 East
I-20 East
I-30 East (probably taking the I-635 east of Dallas to bypass the city)
I-440 East (bypassing southeast Little Rock)
I-40 East (I'll assume I'm just sticking to an interstate instead of the KY parkway route)
I-65 North
I-71 North

Now, if we used European Style:

I-10 El Paso/Houston
I-10 San Antonio/Houston
I-20 Midland/Dallas
1-30 Texarkana/Little Rock
I-40 Memphis/Nashville
I-40 Nashville/Raleigh NC
I-65 Bowling Green/Chicago
I-65 Louisville/Chicago
I-71 Cincinnati/Cleveland

So, if I just feel like writing down instructions, I either better have a good memory of which cities I'm looking for, because if I get lost in Dallas and wind up east of Dallas and suddenly see: I-20 Shreveport/Birmingham,... I'd be stumped. I wouldn't even know if the road was going north, east, south, etc.

Of course, in the US, even without a map, you could just go east to Birmingham and see I-65 North, and realize that's the road you wanted.

In European style you'd see: I-65 Huntsville/Chicago

And every 'control city' better be the same. What if one area had "Indianapolis" listed instead? You get off the road to eat, go to get back on and suddenly you're staring at: I-40 Memphis/Oklahoma City and I-40 Jackson/Nashville.

Imagine if you didn't know that I-65 went through Nashville's downtown? Would you know which way you were still headed on? Did you pass Memphis yet? Or do you still need to get there? Without cardinal direction, the position of the sun doesn't mean much to you. Just get on and guess?

And that is based on the fact that you're taking Interstate freeways the whole time.

From Tucson I could take US70 to I-10 in Lordsburg, NM, I-10 to Las Cruces to I-25 N to US70 to Alamogordo to Roswell to Clovis to Amarillo, TX to I-40 East to Oklahoma City to I-44 through Tulsa, Jopllin, St. Louis, and then I-55 North to I-70 East through Indianapolis, I-465 to I-74 East to Cincinnati. Or take I-64 out of St. Louis to Louisville to I-71 North to Cincinnati.

Using cardinal directions means your 'palette' of directions is four. If you use control cities, the longer the trip, the more cities and where they are that you'll have to remember for your trip.

For instance, American style from Tucson to Cincinnati: East, East, East, East, North, North
Now, European style from Tucson to Cincinnati: El Paso, Houston, Dallas, Little Rock, Memphis, Nashville, Chicago, Cleveland

Less memorization, easier default recognition of direction of travel.

Let's say you get off the freeway, a quick glance at the shield sign at the entrance ramp tells you where to go: EAST I-40. No remembering which city you're looking for or which cities you've already passed on your route.

[CNGL-Leudimin]

Spanish numbering is a total mess. And even worse is when you see all numbers put on simple rectangles. But things becomes more easy with all coloring rectangles have: Blue are motorways, red are national roads and regional roads are, from more importance to less, orange, green and yellow. But then, toll motorways are signed with the same color as free ones, so you have to search for a circle besides the rectangle. And some regions mess things up: Catalonia signs its primary regional roads as they where national roads when they should go in orange (Fomento ministry signs those right) and some motorways like M-45 or A-92 are signed orange like if they weren't motorways (They should go in blue).

[Bickendan]

Typically, Spanish toll roads are AP-x, while the free counterpart is just A-x. A/AP-7 along the Mediterranean is a good example -- though don't get me started on its exit number series!

[J N Winkler]

Typically, Spanish toll roads are AP-x, while the free counterpart is just A-x. A/AP-7 along the Mediterranean is a good example -- though don't get me started on its exit number series!

That rule is generally applicable only to freeway-grade roads that form part of the Red de Carreteras del Estado (the road network under the direct control of Spanish central government).  Even then there are exceptions; metropolitan freeway-standard roads on the RCE often have designations built out of province codes (V-30 in Valencia, B-20 in Barcelona, SE-40 in Seville, etc.).  The convention of using "A" and "AP" to differentiate among tolled and toll-free motorways on the RCE was introduced in the mid-noughties to provide an easy way of differentiating between existing N-roads and their freeway-grade relocations, but now Spain has some toll-free autovías which are getting back their old N-road numbers (N-322 in Valencia comes to mind), and there are some new N-road relocations which are being built to freeway standard but are not being numbered as autovías because they are formally carreteras convencionales (the Benidorm bypass comes to mind as one recent example).

As CNGL says, numbering is a mess.

[CNGL-Leudimin]

Typically, Spanish toll roads are AP-x, while the free counterpart is just A-x. A/AP-7 along the Mediterranean is a good example -- though don't get me started on its exit number series!

Well, things have simplified: AFAIK Valencia bypass, signed as A-7 but originally with kmposts of AP-7, has changed recently its starting point and now continues the kmposts of the Sagunto-Vilavella section (Only god know where its kmpost 0 is: The first one is 274). Don't know about Valencia-Alicante section. BTW, what moron in Google Maps has labelled all of A-7 as AP-7 and left large sections of actual AP-7 as E15 only...

[firefly]

European style seems to imply you ONLY take the freeway between major points, and your basis of travel is getting to that freeway as quickly as possible.

If I'm driving from Tucson AZ to Cincinnati OH, this is how I do it in the US:

I-10 East
I-20 East
I-30 East (probably taking the I-635 east of Dallas to bypass the city)
I-440 East (bypassing southeast Little Rock)
I-40 East (I'll assume I'm just sticking to an interstate instead of the KY parkway route)
I-65 North
I-71 North

Now, if we used European Style:

I-10 El Paso/Houston
I-10 San Antonio/Houston
I-20 Midland/Dallas
1-30 Texarkana/Little Rock
I-40 Memphis/Nashville
I-40 Nashville/Raleigh NC
I-65 Bowling Green/Chicago
I-65 Louisville/Chicago
I-71 Cincinnati/Cleveland

It would actually read more like this:

Houston, Dallas, El Paso I-10
Houston, San Antonio, Dallas I-10
Dallas I-20
Memphis, Little Rock I-30
Memphis I-40
Nashville I-40
Chicago, Louisville I-65
Cleveland, Cincinnati I-71

So all you have to memorise are 4 control cities additional to your destination. Which shouldn't be that difficult. Well, it is at least easier than keeping 6 or more road numbers as in this case.

So, if I just feel like writing down instructions, I either better have a good memory of which cities I'm looking for, because if I get lost in Dallas and wind up east of Dallas and suddenly see: I-20 Shreveport/Birmingham,... I'd be stumped. I wouldn't even know if the road was going north, east, south, etc.

But you would know that you're heading for Birmingham which is south of your preferred route. So you have either to turn or to consult a map for better option.

Of course, in the US, even without a map, you could just go east to Birmingham and see I-65 North, and realize that's the road you wanted.

Yet, you would only know that you could turn onto I-65 without consulting a map when you're already near Birmingham.

And every 'control city' better be the same. What if one area had "Indianapolis" listed instead? You get off the road to eat, go to get back on and suddenly you're staring at: I-40 Memphis/Oklahoma City and I-40 Jackson/Nashville.

In a properly maintained signage system a control city is repeated on every sign until the city (or the road leading to this city) is reached. So you can follow it until your next control city appears.

Imagine if you didn't know that I-65 went through Nashville's downtown? Would you know which way you were still headed on?

Yes, you would. The signs always tell you where you're heading.

Did you pass Memphis yet?

You're more likely to ask this question when navigating by numbers and cardinal directions only.

Or do you still need to get there? Without cardinal direction, the position of the sun doesn't mean much to you. Just get on and guess?

Just because we're not navigating by cardinal directions doesn't mean we don't care about them.

And that is based on the fact that you're taking Interstate freeways the whole time.

A non-interstate wouldn't be a sensible choice on this particular occasion.

From Tucson I could take US70 to I-10 in Lordsburg, NM, I-10 to Las Cruces to I-25 N to US70 to Alamogordo to Roswell to Clovis to Amarillo, TX to I-40 East to Oklahoma City to I-44 through Tulsa, Jopllin, St. Louis, and then I-55 North to I-70 East through Indianapolis, I-465 to I-74 East to Cincinnati. Or take I-64 out of St. Louis to Louisville to I-71 North to Cincinnati.

Using cardinal directions means your 'palette' of directions is four. If you use control cities, the longer the trip, the more cities and where they are that you'll have to remember for your trip.

The number of control destinations doesn't necessarily increase by the length of a journey. It can though. It depends on the route and the size of the control city. Chicago for instance could very well be signed on I-90 from Boston and Seattle onwards. If you stayed on this route you could follow a single control city for several thousands km.

For instance, American style from Tucson to Cincinnati: East, East, East, East, North, North

The American way requires to memorise the road numbers as well. You forgot about them.

Now, European style from Tucson to Cincinnati: El Paso, Houston, Dallas, Little Rock, Memphis, Nashville, Chicago, Cleveland

Less memorization, easier default recognition of direction of travel.

As I mentioned before one could find its way with less control cities depending on the directional signage. It's still easier to memorise a chain of cities than a handful of number especially when your familiar with the general geography.

Let's say you get off the freeway, a quick glance at the shield sign at the entrance ramp tells you where to go: EAST I-40. No remembering which city you're looking for or which cities you've already passed on your route.

In Europe you'd get the choice between Nashville I-40 and Memphis I-40. Knowing your route you'd pick Nashville. One has to think a bit more in this case I admit.

[Scott5114]

Keep in mind that it's not really a big deal that you're following six road numbers, as you're going to be on each one of them for several hours. From Tucson to the I-20 turnoff is a six hour drive, then it's six more hours to Dallas, and when you reach I-40 you'll be in an entirely different state. Chances are slim you're going to do Tucson to I-20 to I-30 in one day, so you don't even really have to worry about "remembering" all of the numbers, since you'll be sleeping in between them, and most travelers would need to refresh their itinerary in the morning before setting off anyway.

[kphoger]

This is all only tangental to the OP, though.  European highways are numbered.  The question was why they don't use US-type shields for those numbers, not whether it's 'better' to navigate by control cities or route numbers, or whether it's 'better' or not to use cardinal directions–which has already been discussed at length in other threads.