Expressways vs. non-expressways, Europe vs. US

[Tom958]

I'm trying to flesh out a narrative, kind of a research project-thought exercise regarding rural multilane non-freeway highways, and I want to make sure I'm presenting an accurate representation of reality. My goal is to create a post or series of posts illustrating what I've found through  Streetview/Google Maps links or screenshots. If you're so inclined, I'd appreciate it if you'd post examples (or counterexamples) to illustrate (or contradict) my points.

In the US, it's common practice in many states to build these highways as at-grade facilities with little or no control of access either to abutting properties or to intersecting roads, largely through dualization (twinning) of legacy highways. In Europe, though, the prevailing philosophy seems to be that if a highway needs to be four lanes, it also needs to have some degree of grade separation and access control. Obviously, the best way to accomplish this is to build on new location, often with reduced standards compared to motorways/autoroutes/autostrada in order to cut costs. However, to some degree the same practices can be applied to legacy two-lane roads. These include:

Impermeable medians which preclude cross-median turns, imposing RIRO (or, in the UK, LILO) operations upon any intersecting roads and driveways.

Narrow, barrier medians, which reduce right-of-way and (usually) grading requirements.

Very economical grade separation structures. For bridges over the highway, minimal requirements for side clearances plus narrow barrier medians allow span lengths to be shorter and superstructures to be less substantial. Admittedly, European motorways are already more conservatively designed in this regard, but the difference is still visible in many cases.

For crossings under the highway, culverts are often used, as well as steel sheet piling for abutments. Sometimes big corrugated metal pipes are used for country lanes.

Very ad-hoc interchange layouts, often with ramps connecting to whatever's handy instead of in recognizable diamond or folded diamond interchanges. I saw one place in France with a diamond interchange with only three ramps. To make the missing connection required traveling for seven kilometers along various parallel roads to the next interchange!

Not an economy measure, but interchanges are generally more frequent compared to those on motorways, especially when providing U-turn opportunities on highways with RIRO/LILO access to side roads and/or abutting properties.

Use of roundabouts as substitutes for interchanges. A ten-mile segment of the A470 in Wales has no intersections and no interchanges, just grade-separated crossings and roundabouts. I also stumbled upon this recent example in France. N154 is new and, to my eye, indistinguishable from a free autoroute, and N12 is apparently intended for four-laning in the foreseeable future, but they intersect at a roundabout with a couple of local roads thrown in for good measure.

That's it for this post. Next, some discussion of national differences, which I really don't know enough about. 

[Chris]

According to FHWA data, the United States has 144,000 kilometers / 89,000 miles of rural four lane arterial highways that are not freeways. This is larger than the Interstate Highway system.

This type of at grade, four lane divided highways has not been built in most of Europe on any significant scale, except in the former USSR, where they are a bit more common due to the absence of controlled-access highways in most areas.

One of the reasons is that the European population density is much higher. Any four lane highway would have a large number of signalized intersections or perhaps multilane roundabouts. This is a primary reason why most non-motorways are built as controlled-access expressways. The rural population density would also make four lane upgrades of existing roads difficult if not impossible.

The European network of controlled-access highways is denser than that of North America. Even in the Eastern United States, Interstate Highways are typically around 200 kilometers apart. In Europe, this is often not much more than 100 kilometers except in very low density regions like Scandinavia or in underdeveloped regions like Southeastern Europe.

The European motorway system totals around 100,000 kilometers, on an area of roughly 4.5 million square kilometers excluding the former Soviet Union. By comparison, the contiguous United States has some 100,000 kilometers of freeways on an area of roughly 8 million square kilometers. This means that there are almost twice as many controlled-access highways relative to land area, which has reduced the need for at-grade four lane highways.

So the U.S. has had a greater need to upgrade the U.S. Highway system to four lanes on busier corridors where Interstate Highways would be too far out of the way. The U.S. Interstate grid system also has a number major missing links between 1M+ metro areas, for example from St. Louis to Minneapolis, Dallas to Denver, Columbus to Detroit, or Memphis to Kansas City. This type of missing links do not exist in the parts of Europe that have a built-out motorway system. They only occur in places that aren't as developed yet, mostly in the former Eastern Block.

[Rothman]

Hm.  That number seems too high to me.  Wonder if the data was intrepreted correctly.