Interstate Airports?

“The Eisenhower interstate system requires that one mile in every five
must be straight. These straight sections are usable as airstrips in
times of war or other emergencies.”

This was sent to me as a “fact”, but it sure sounds like a UL to me. Anyone have any knowledge on this?

On the same subject, I once heard that the numbering system was determined by the % of USA land mass to the south and west of the road - so I90 has 90% of the continental US to the south and west of the line it creates.

Sounds fishy but I don’t have a US map in front of me to “eyeball” the potential accuracy of this statement. Anyone know? This has probably been discussed before - if so, please give me a link. Thanks!

I’ve heard this too, and of course it sounds like a UL. However –

There were all sorts of weird defense plans going on the 1950s, when the Interstate Highway System was first designed. I personally know of little municipalairports out in the Great Plains that had plowed extensions several thousand feet long extending out from their one small runway into the wheat fields beyond. The explanation I ALWAYS heard was that they were “emergency landing strips for the Air Force.” So it’s not inconceivable that some of the stretches designed in the late 1950s and early 1960s could have had straightaways designed into them for just this purpose.

I don’t think that’s correct. An Interstate highway would have to go border-to-border in order for that statement to be true.

For example, I-44 starts at St. Louis and ends at (I think) Dallas. Can we say that 44% of the US land mass is South and West of an incomplete line that runs from NE to SW?

Planes DO land on interstate highways. It’s been done before. A few years ago a private plane landed on a busy Interstate in LA.

Don’t think a 747 or other jumbo jet could land on one. As soon as they got to an overpass their wings would shear off.

Powers106: On the same subject, I once heard that the numbering system was determined by the % of USA land mass to the south and west of the road - so I90 has 90% of the continental US to the south and west of the line it creates.

Generally, the interstate numbers increase west to east and south to north. But I don’t think they’re based on any definate percentage. Plus, not all interstates go completely across the country, not even the multiples of 5 and 10.

Then there’s I-99, which is a pork-barrel project in Pennsylvania. It should be a spur off some other highway, not necessarily an interstate. Congressman Bud Shuster even got it named after him. (The BS Highway, now that apropos!) But hardly 99% of the US is SW of this road. If anything, it should be in Maine, along the Canadian border.

I-99 description
The Anti Bud Shuster/Interstate 99 Page

I have nothing useful to add to this thread, so I’ll add some useless stuff.

The Swedes have designed several generations of jet fighters to take off from main highways. The plans include rapid removal of telephone and electrical wires which might be in the way.

I don’t think the percentage associated with Interestate Highways is “south and west”, I think it is “south or west”. That is, if it is an odd-numbered highway, its last two digits are the percentage of land to its west (i.e. I-205 is 5% of the way from the west coast). I-90 or I-290 would be 10% down from the Canada border, so they could be in New York or Washington or Minnesota, or all three. That’s a hypothetical, I don’t even know if there is an I-290.

I’m not sure if this is true in practice, but I gather that was the intention. As for diagonal roads, well, they are always considered north-south or east-west. So I guess they have to pick a point where the road is really supposed to be…?

Nothing I write about any person or group should be applied to a larger group.

  • Boris Badenov

On the second question, if the important part of that is the exact percentage of land mass, then no that is not true.

As to the one in five rule, that’s a new one on me. I’ll run it by the roadgeeks mailing list and see what flies back.

The numbering was simply designed to go in the opposite direction from the 1923 system of “U.S.” state highways so that there would be less likelihood of the I- numbers running confusingly parallel to the US- numbers. U.S. 1 runs down the East coast from Maine to Florida. U.S. 2 runs from Michigan’s U.P. across the top of the country to Washington. The general numbering of those roads moved east-to-west and north-to-south. When the Interstates were designed, they initially went the opposite directions with low I- numbers in the West and South and higher numbers occurring as you moved East and North. The older convention of east-west roads using even numbers and north-south roads using odd numbers was left in place so that the pattern would be familiar but the numbers would not be confused.

More recent highways in each system have violated the original “rules” as highways were added to the systems after the original layouts were completed.


As far as I know, it is true about interstates being able to handle planes. The reason the interstate was built was specifically for the military and ease of transport of it.

Yer pal,

I remember reading a CNN online article about
this. The article was talking about how the
air force practiced landing on the freeways
every so often. I however have my doubts that
1 out of every 5 miles needs to be set up for
this. There are lots of stretches through
mountains and cities that this would not be

It’s an UL that there is a specific stretch of Interstate every X miles that can be used as a landing strip.

That doesn’t change the fact that airplanes can and do land on roads. Small airplanes, anyway.

A typical runway for a small airport might be 3500’ long, and 50’ wide. Typical dimensions for a straight stretch of highway. Many private airstrips are simply manicured grass, perhaps 2000’ long. I’ve landed on a 2000’ grass runway with no problems, and in a fairly high-performance airplane.

The biggest problem with landing on roads is power lines. They are hard to see from the air, and sometimes cross roads haphazardly. For instance, a farm might be built on one side of a road and the power lines are on the other. Rather than dig under the road a construction crew will simply cross the lines over top. These aren’t marked on maps, and are impossible to see during the approach to landing. So it’s extremely hazardous to land on a road intentionally. In fact, it’s dangerous enough that some pilots will opt to land an airplane in a farmer’s field rather than on a road if they have an engine failure.

*tomndebb: U.S. 2 runs from Michigan’s U.P. across the top of the country to Washington. *

US 2 also runs through New England.

If it’s like other US routes, it probably runs concurrent with other highways between Michigan and New England.

More Interstate Trivia:

I-77 and I-81 run concurrent in Virgina for a few miles. I-81 generally runs NE/SW, I-77 runs NW/SE, and both are labels either running North or South.

But in the concurrent strip, I-81 is labeled North and I-77 is South (opposite in the other lanes).


More Highway triva–though not interstate:

There is a stretch of road in SC where US 17 and US 21 run together.

At the same time, for a few miles, you’re on US 17 heading north and US 21 heading south.

Back to topic: still don’t know about the airports.

On a tangent, I understand that what the OP hypothesizes is actually true in Switzerland. I saw a show about the Swiss Army on TV (OK, not a very good source of reliable information, but it’s the only one I have here). Apparently, the major highways in Switzerland have dividers that can be taken up easily, so if a military aircraft needs to land, a ground crew can take up the median divider and the plane can land.

I present this only as something I heard; I have no independent assurance that it’s true.

Never attribute to malice anything that can be attributed to stupidity.
– Unknown

A search of the Federal Highway Commision web site revealed much information on the “Dwight D. Eisenhower System of Interstate and Defense Highways” AKA the “Eisenhower Interstate System”. The site stresses national defense as a major impetus for building the interstate system (hence the word “defense” in the official title), but makes no mention of a contingency for landing aircraft, military or otherwise, on an interstate highway. Doesn’t necessarily mean it ain’t so, but I’ve found no reliable source that says it is, either.

The overwhelming majority of people have more than the average (mean) number of legs. – E. Grebenik

I wouldn’t be so quick to call the landing strip idea an UL. The Interstate Highway system was definitely built with a military application in mind. The following comes from a recent on-line article called 40 Years of the US Interstate Highway System.

“One of the principal reasons for building the interstate highway system was to support national defense. When the system was approved — during one of the most instable periods of the Cold War, national security dictated development of an efficient national highway system that could move large numbers of military personnel and huge quantities of military equipment and supplies.”

I’ve also been told (though I just did a search and couldn’t find a cite) that the Insterstate overpasses were designed in such a way that even if they were destroyed (bombed, sabotage, etc) military traffic could be routed around them. If you look at most of the overpasses built through the early eighties, this appears to be true. I think after a certain point, they relaxed some of the war footing regulations to take into account the realities of the new, tighter, American landscape.

Also, I know that if *I</> were building a national, intercontinental road system during a time of high international tensions, I would take the opportunity to make sure that parts of it cold be used as impromptu landing strips.

As I said, no cites, but makes sense to me.

This is a classic alt.folklore.urban topic

The a.f.u search engine on is wiggin out so I can’t search, but IIRC most miliary aircraft would be so heavy that they’d tear up the asphalt. Also, the resulting damage to the plane would be so great that flying it again would be impossible.

Imagine having an unflightworthy B-52 stranded in the middle of a severely torn up I-95. It’d be a huge pain to move the damn thing, let alone repair it later.

Back off, man. I’m a scientist.


You’re absolutely right on the first point! I remember being surprised to find a U.S. 2 when visiting new England a few years ago.

I’m not sure what you meant by your second statement. U.S. 20 (coming out of New York) and U.S. 6, U.S. 322, and U.S. 422 (coming out of Pennsylvania) all run to or through Cleveland, but U.S. 2 does not. Between Michigan and New England and upstate New York is this not-very-small gap in the U.S. called Ontario (with a touch of Quebec). I’m pretty sure there are not any U.S. highways in those areas. Any road that does not loop south of Lake Erie has a gap in it.


I got a couple replies to putting the OP before hardcare highway fans. One of the responders is known to me from his earlier good answers. <hr> ‘Yes, it is now obsolete, but since the interstate system was originally intended for national defense one in five miles had to be straight.’

‘This is an obsolete rule, dropped several decades ago.’