Urban offramps built with curves to stop enemy troops?

[bugo]

http://www.okhistory.org/audio/okjourneys050810.mp3

This audio file claims that on urban highways, offramps leading into town were built with curves to slow down invading enemy troops, and onramps leading out of town were built straight to make evacuation easier.  This is the first I've ever heard of this.  Is this true or just legend?

[jwolfer]

http://www.okhistory.org/audio/okjourneys050810.mp3

This audio file claims that on urban highways, offramps leading into town were built with curves to slow down invading enemy troops, and onramps leading out of town were built straight to make evacuation easier.  This is the first I've ever heard of this.  Is this true or just legend?

I dont thing invading armies follow the rules of the road too well.  But I can see the reasoning.  The justification for the Interstate Highways was for defense

[realjd]

I'm calling BS. I'd file that away with the "legend" about 1 mile every 10 being straight for airplane emergency landings.

[triplemultiplex]

Sounds like an urban legend to me; and not a very good one at that.  At least the one about incorporating straight stretches into interstates that could be re-purposed as runways has the advantage of there actually being lots of straight stretches of interstate highway.  This one is unsupported by the existence of these types of ramps with any sort of consistency to support such an outlandish idea.

Even if it was the case, I can think of a bunch of other reasons why it would be.
For example, one might make the off ramps curvier so traffic is encouraged to slow down before joining surface streets while straighter on ramps would help traffic get up to freeway speed faster and make for less disruptive merging.

[J N Winkler]

Even if it was the case, I can think of a bunch of other reasons why it would be.

For example, one might make the off ramps curvier so traffic is encouraged to slow down before joining surface streets while straighter on ramps would help traffic get up to freeway speed faster and make for less disruptive merging.

I don't buy "encourage traffic to slow down" as a design criterion for off-ramps.  It certainly comes into play in designing traffic calming, but in the context of freeway design it is so easily countered by the suggestion "curves increase the likelihood of run-off-the-road accidents" that I think the vast majority of freeway designers would have steered clear of it.  It is not for nothing that relatively tight scissors ramps on early freeways now have Moskowitz signs in many states (the warrant for these, at least in California, is at least one death attributed to excess speed on the curve).

Instead, to the extent that there is any actual difference in design between off-ramps and on-ramps, I think ROW considerations plus the requirement that the ramp design speed be a minimum percentage of the mainline design speed are the ruling constraints.  It makes more sense to provide additional relatively straight length on on-ramps because cars typically need more length to accelerate over a given speed band (say 20 to 60 MPH) than to brake over the same band.

[agentsteel53]

Moskowitz signs

what is this? 

[NE2]

This legend dates back at least to Asimov's The Caves of Steel (1953), where the (moving sidewalk) expressway exit to Spacetown twisted and turned to prevent mobs from forming.

[J N Winkler]

A Moskowitz sign (named after Karl Moskowitz, who did the early research into its effectiveness) is an 8' x 8' oversized sign warning of a sharp curve or signal ahead condition.  In California these signs can be formatted either as diamonds or squares but the latter is more usual.

Example:

Royal Oaks Dr./Exposition Blvd. exit on North Sacramento Freeway (opened 1947)

[Alps]

If either a) Anyone but you and the Moskowitz family calls them Moskowitz signs, or b) that sign is within 12 inches of 8 feet height or width, I will donate my left patella to charity and use the proceeds to buy a brick at Camden Yards in your honor.

[agentsteel53]

that does not look 8x8 to me.  6x6?

[J N Winkler]

If either a) Anyone but you and the Moskowitz family calls them Moskowitz signs, or b) that sign is within 12 inches of 8 feet height or width, I will donate my left patella to charity and use the proceeds to buy a brick at Camden Yards in your honor.

Keep your left knee--the design life of artificial replacements maxes out at about ten years.

They were called "Moskowitz signs" in a letter from Caltrans to the Oregon Highway Department (which was interested in the concept) that I found years ago in the signs and signals file at the Caltrans library.  Moskowitz (with Theodore Forbes) also co-authored the mixed-case sign lettering study.

that does not look 8x8 to me.  6x6?

It does look kind of small.  I would rather have posted a photo which I used to have on my Fotopic site, showing a square-format 30-MPH double-turn sign which I think is actually 8' x 8' in size, on SR 28 with Lake Tahoe in the background.  Unfortunately, Fotopic went bust a couple of years ago and I don't have this picture ready to hand on any of my local HDs.

[agentsteel53]

It makes more sense to provide additional relatively straight length on on-ramps because cars typically need more length to accelerate over a given speed band (say 20 to 60 MPH) than to brake over the same band.

explain, then, the predilection for building interchanges at the bottoms of valleys.

the most dangerous interchange I can think of in southern California is Mira Mesa Blvd at 805, because it has 3 lanes of 20mph hairpin cloverleaf drop to 1 with about 100 feet of acceleration room ... at the beginning of a 5.5% uphill incline - with mainline traffic, having come down the hill, doing 80-85mph.

I drive that ramp every day as part of the commute.  statistically speaking, if I am to get into a severe accident, it will happen there.

[elsmere241]

Along those lines . . .

I'm too lazy to run upstairs and check the details, but in Roads to Quoz William Least Heat-Moon tells of a road in rural north Florida that seemed to go nowhere (he may have even called it "The road to nowhere") but was in the perfect position to be used as a runway for small airplanes.  (Specifically, the local drug dealers.)

[blawp]

It makes more sense to provide additional relatively straight length on on-ramps because cars typically need more length to accelerate over a given speed band (say 20 to 60 MPH) than to brake over the same band.

explain, then, the predilection for building interchanges at the bottoms of valleys.

the most dangerous interchange I can think of in southern California is Mira Mesa Blvd at 805, because it has 3 lanes of 20mph hairpin cloverleaf drop to 1 with about 100 feet of acceleration room ... at the beginning of a 5.5% uphill incline - with mainline traffic, having come down the hill, doing 80-85mph.

I drive that ramp every day as part of the commute.  statistically speaking, if I am to get into a severe accident, it will happen there.

Looking at the Sat. View there is still plenty of width on that infamous despite the lane drop. It's also an onramp with traffic moving pretty carefully. Moorpark Rd and 101 is similar to this. 3 lanes to 1.

[J N Winkler]

explain, then, the predilection for building interchanges at the bottoms of valleys.

I don't think such a predilection in fact exists, at least as a matter of design policy.  In some areas with topographical variation (such as southern California), it may be a natural result of the roads which preceded freeway development tending to hug valley floors.  In flat country minor roads tend to be carried over the freeway because they are subject to more relaxed standards for forward sight distance and therefore can achieve the desired change in profile with less earth movement.

the most dangerous interchange I can think of in southern California is Mira Mesa Blvd at 805, because it has 3 lanes of 20mph hairpin cloverleaf drop to 1 with about 100 feet of acceleration room ... at the beginning of a 5.5% uphill incline - with mainline traffic, having come down the hill, doing 80-85mph.

I drive that ramp every day as part of the commute.  statistically speaking, if I am to get into a severe accident, it will happen there.

I don't think it is that bad.  Yes, three lanes merge into one, but the capacity of an individual lane on a low-speed loop ramp is much less than the capacity of one lane on a freeway, and this ramp becomes a gained lane on the freeway mainline.

The operational characteristics, as you describe them, are not dissimilar to a ramp I use fairly frequently:

Zoo Blvd. on-ramp at I-235

Two ramp lanes become one upstream of the merge nose, which tends to reduce the headway between vehicles, and then all ramp traffic must merge because the ramp lane does not become a gained lane on the mainline.  Visibility is poor for judging a merge and the merging area is so short that a single pair of cars engaged in an overtaking maneuver can "lock out" a car wishing to merge.  It is not uncommon for cars either to stop at the bottom of the ramp or to finish merging maneuvers from the shoulder.

[kphoger]

The operational characteristics, as you describe them, are not dissimilar to a ramp I use fairly frequently:

Zoo Blvd. on-ramp at I-235

Two ramp lanes become one upstream of the merge nose, which tends to reduce the headway between vehicles, and then all ramp traffic must merge because the ramp lane does not become a gained lane on the mainline.  Visibility is poor for judging a merge and the merging area is so short that a single pair of cars engaged in an overtaking maneuver can "lock out" a car wishing to merge.  It is not uncommon for cars either to stop at the bottom of the ramp or to finish merging maneuvers from the shoulder.

I agree that the Zoo Blvd interchange is inadequate in the ways you describe.  Most of the problem there would be alleviated by extending the acceleration lane so that entering traffic can reach highway speed.  I find short acceleration lanes to be a chronic problem in this area; for example, try accelerating from eastbound Pawnee onto northbound I-135 in time to merge (I realize that bridges are involved, so improving it would be an undertaking):  http://goo.gl/maps/bacI

Back to the original topic...  Seriously, how much would that slow down invading troops?  A few seconds, perhaps?  With a huge invasion causing a tailback (????), maybe a minute?

[jwolfer]

.....
For example, one might make the off ramps curvier so traffic is encouraged to slow down before joining surface streets while straighter on ramps would help traffic get up to freeway speed faster and make for less disruptive merging.

I used to think this way..  Going west out of Jacksonville on I-10 many exits are this way. You have to slow down to exit, but the entrance ramp is pretty curvy, so note easy to get up to highway speeds.  This stretch of road is one of the older sections of rural interstate in Florida.

[bugo]

I figured the story was bullshit, now I'm convinced.  How do historical societies get things wrong so often?

[Mr_Northside]

"Sir - What do you think our chances of victory really are?"

"Based on Intelligence reports, not very good.  They have a TON of curvy ramps."

"Shit."

[D-Dey65]

I figured the story was bullshit, now I'm convinced.  How do historical societies get things wrong so often?

I suppose the same way they incorrectly claim that Thomas Jefferson said "Dissent is the highest form of Patriotism," and Benjamin Franklin said "Don't trust the Jews." The two ramps that JN Winkler showed us don't exactly convince me that slowing down enemy troops is what the designers had in mind.

[Hot Rod Hootenanny]

I figured the story was bullshit, now I'm convinced.  How do historical societies get things wrong so often?

Because they are manned by volunteers and not professionals. (So says he who works at a local historical society)