What does AARoads consider the difference between...

[shadyjay]

Why would you have a fully grade separated, limited access highway that is undivided? I would think separating opposite direction movements would do more for safety, not to mention be cheaper to implement, than removing 90 degree crossings.

New Hampshire has been doing this for quite some time.  Look at the US 3 bypass around Laconia, the Keene bypass, Hillsborough Bypass, NH 101 in Milford, and, until the 1990s, most of NH 101 between (east of) Manchester and the seacoast.
Granted, these were all pretty much built as bypasses. 

Vermont jumped on the bandwagon with VT 289 and, most recently, VT 279.

RI has the Westerly Bypass, though it does have a jersey barrier.

[cl94]

Why would you have a fully grade separated, limited access highway that is undivided? I would think separating opposite direction movements would do more for safety, not to mention be cheaper to implement, than removing 90 degree crossings.

New Hampshire has been doing this for quite some time.  Look at the US 3 bypass around Laconia, the Keene bypass, Hillsborough Bypass, NH 101 in Milford, and, until the 1990s, most of NH 101 between (east of) Manchester and the seacoast.
Granted, these were all pretty much built as bypasses. 

Vermont jumped on the bandwagon with VT 289 and, most recently, VT 279.

RI has the Westerly Bypass, though it does have a jersey barrier.

If it's built wide enough, head-ons are less of a concern. A bunch of super twos (i.e. US 33 in SE Ohio) are built with full-width shoulders and 12-foot lanes. Sometimes, you just don't need more than 2 lanes. Removing cross traffic allows for higher speeds, increases safety on the crossroad, and allows slow-moving traffic (i.e. farm vehicles) to cross without slowing everything down or causing an accident. If more lanes are needed at a later date, it can be upgraded to a divided limited-access highway quite easily.

I actually wonder why more places don't have super twos.

[cpzilliacus]

I actually wonder why more places don't have super twos.

Head-on crashes involving attempts to pass.  I have a relative that was severely injured in a such a wreck on a Super-2 in one of the Nordic nations.

I have seen Super-2 highways in the U.S. and elsewhere that have a steel barrier (sometimes made of box rail) to deter attempts to pass, but that also means that one slow vehicle will cause a traffic to back up behind it.

[dfwmapper]

So you do what some of the Nordic countries have done and turn 10+12+12+10 into 4+12+12+12+4 with the middle lane serving as a passing lane alternating between each direction every mile or two. Put a continuous rumble strip down the center to alert inattentive drivers if they accidentally cross over.

[riiga]

Indeed, converting super-twos into 2+1 roads is very cheap and reduces fatal accidents almost entirely assuming a central divider is used, typically a wire barrier in Sweden.

10+12+12+10 into 4+12+12+12+4

[dfwmapper]

Converting a road from two 10' wide shoulders and two 12' wide travel lanes into two 4' wide shoulders and three 12' wide lanes. Assuming the "full-width shoulders" cl94 was referring to are indeed 10'.

[Big John]

Not sure how the Nordic countries construct their highways, but shoulders on American highways usually have a lot thinner pavement if it is paved since they are supposed to be sparsely used by traffic, so they need to be reconstructed to full depth if they are to be converted to live lanes (being permanent or temporary to accommodate traffic during construction projects)

[riiga]

Converting a road from two 10' wide shoulders and two 12' wide travel lanes into two 4' wide shoulders and three 12' wide lanes. Assuming the "full-width shoulders" cl94 was referring to are indeed 10'.

Ah, it never occurred to me that you meant width in feet. I thought you might be on about number of lanes, but that made no sense and would probably be even easier to mistake in metric as 3+4+4+3 if you leave out the unit. 

Our super-twos typically have a shoulder of 2-3 meter on each side and two 4 meter lanes, the total width being 13 meter. This was most commonly converted to three lanes of 3.5 m, a median of 1-1.5 m and the rest shoulder. I've seen some narrower and wider configurations though, both 12.25 m and 14 m.

Not sure how the Nordic countries construct their highways, but shoulders on American highways usually have a lot thinner pavement if it is paved since they are supposed to be sparsely used by traffic, so they need to be reconstructed to full depth if they are to be converted to live lanes (being permanent or temporary to accommodate traffic during construction projects)

I think our roads are the same thickness all the way, however the shoulders aren't repaved as often as the lanes. Some converted roads required reinforcement of the shoulders though which made them more expensive to convert than just repainting and putting up a barrier. Still cheaper than building a motorway by far.

[cpzilliacus]

So you do what some of the Nordic countries have done and turn 10+12+12+10 into 4+12+12+12+4 with the middle lane serving as a passing lane alternating between each direction every mile or two. Put a continuous rumble strip down the center to alert inattentive drivers if they accidentally cross over.

Of course, the Nordics do not measure lane widths in feet.    EDIT: As riiga pointed out.

There are places where the middle lane alternates back and forth to provide a passing lane.  I have also seen Super-2's with just one lane in each direction, and nothing more.  Rumble strips seem disfavored - a "hard" steel barrier is the preferred solution.

[bsmart]

So it would be the Atlantic City Freeway?

Expressway does have a bit of a weight to it...it does say that it will take you there faster than the regular roads.

I always figured and expressway could be tolled while a freeway was never tolled.  Other than that they seemed to be interchangeable here in Maryland and what I saw elsewhere in the midatlantic

[bzakharin]

So it would be the Atlantic City Freeway?

Expressway does have a bit of a weight to it...it does say that it will take you there faster than the regular roads.

I always figured and expressway could be tolled while a freeway was never tolled.  Other than that they seemed to be interchangeable here in Maryland and what I saw elsewhere in the midatlantic

So it would be the Atlantic City Freeway?

Expressway does have a bit of a weight to it...it does say that it will take you there faster than the regular roads.

I always figured and expressway could be tolled while a freeway was never tolled.  Other than that they seemed to be interchangeable here in Maryland and what I saw elsewhere in the midatlantic

This may be why the term "freeway" hasn't caught on with the general public (in many places). Also why the difference between "highway" and "expressway" isn't that clear to the public (in many areas). Is "high" better than "express" or vice versa? That's just the consequence of using compositional coinages, I guess.

[cpzilliacus]

So it would be the Atlantic City Freeway?

Expressway does have a bit of a weight to it...it does say that it will take you there faster than the regular roads.

I always figured and expressway could be tolled while a freeway was never tolled.  Other than that they seemed to be interchangeable here in Maryland and what I saw elsewhere in the midatlantic

So it would be the Atlantic City Freeway?

Expressway does have a bit of a weight to it...it does say that it will take you there faster than the regular roads.

I always figured and expressway could be tolled while a freeway was never tolled.  Other than that they seemed to be interchangeable here in Maryland and what I saw elsewhere in the midatlantic

Maryland does not like to call its roads freeways, even those with a functional classification of freeway.  The only roads classified as a freeway with that word in the name are the National Freeway (I-68); the Patuxent Freeway (Md. 32 from I-97 to Md. 108); the short section of the Anacostia Freeway (I-295) that is not in D.C.; and the Arundel Freeway (Md. 10).

Other roads functionally classified as freeways (but not called that) include:

Capital Beltway (I-495 and I-95);
Baltimore Beltway (I-695);
JFK Highway (I-95);
John Hanson Highway (U.S. 50 and U.S. 301);
Baltimore National Pike (I-70 and U.S. 40);
Harrisburg Expressway (I-83);
Jones Falls Expressway (I-83);
Dwight D. Eisenhower Highway (I-70 west of Fredrick);
Dwight D. Eisenhower Highway, f/k/a Washington National Pike (I-270);
Baltimore Harbor Tunnel Thruway (I-895); and
InterCounty Connector (Md. 200).

[Buffaboy]

I learned this from the AARoads glossary last night.