Why no official "Alternate" Interstate highway designation?

[Pink Jazz]

Considering that both the Interstate and U.S. route systems have business routes, how come the Interstate Highway System doesn't have an official "Alternate" designation like the U.S. route system?

Perhaps if there were such a designation, just as Business Interstates are signed with green shields, Alternate Interstates could be signed with either brown shields, or all red shields.

[roadfro]

The Interstates are supposed to be the best and quickest route between points, which defeats the purpose of an alternate route...

[kj3400]

The Interstates are supposed to be the best and quickest route between points, which defeats the purpose of an alternate route...

But what happens when there is an accident/natural disaster/insert calamity here, and the interstate is closed?

[briantroutman]

But what happens when there is an accident/natural disaster/insert calamity here, and the interstate is closed?

Some states have permanent detour signs posted as a bypass of likely trouble areas, and the signs are folded or otherwise hidden when not needed. During a weather event or other emergency, the signs are exposed, giving motorists an easy-to-follow detour around the blockage.

In my view, the problem with "alternate"  (of any kind, including US or state routes) is that "ALT"  is a vague descriptor. Motorists would probably assume the alternate route is not the preferred route, but even if it's not preferred, is it a reasonable substitute, or is it a stopgap that's really intended for emergency use only? Is it a way to avoid traffic backups on the congested main route, or is it a scenic option for Sunday sightseers?

At least banners like "truck" , "bypass" , and "business"  make it clear what purpose those routes serve in relation to the main road.

[kj3400]

But what happens when there is an accident/natural disaster/insert calamity here, and the interstate is closed?

Is it a way to avoid traffic backups on the congested main route, or is it a scenic option for Sunday sightseers?

Isn't there a 'scenic byway' banner for that latter option? If not, that would be a good idea.

[DandyDan]

And technically speaking, isn't I-670 in Kansas City also signed as Alternate I-70?  I seem to recall that being true once.  The one definitive thing I can say about that is that it is the shorter route.

[US71]

And technically speaking, isn't I-670 in Kansas City also signed as Alternate I-70?  I seem to recall that being true once.  The one definitive thing I can say about that is that it is the shorter route.

It still was back in June.

[Laura]

Yeah. In Ohio, there are Alt I-70 shields that I can only assume are detours from the interstate if it is backed up or closed.


iPhone

[dgolub]

There's a section of NY 25 in Jericho, New York, that has some Alternate I-495 signs on it.  Not an official designation, I suppose, but the signs are there.

[spooky]

Neither brown nor red is an appropriate color for an interstate shield.

[US81]

There's a section of NY 25 in Jericho, New York, that has some Alternate I-495 signs on it.  Not an official designation, I suppose, but the signs are there.

I think I remember having seen Alt I-45 signs south of Houston and possibly Alt I-37 signs around Corpus Christi, too. This would have been many years ago; I'm thinking they were supplemented and then supplanted by Hurricane Evacuation Route signs. Anyone else? or was it just a dream.....

[hubcity]

This is one thing they do well on Germany's Autobahn system. Between every interchange (wherever possible, and they do their best to make it possible) there is a set of local roads designated with permanent signage that provides an alternate route between the interchanges, in case something blocks the main highway.

Here's some more info: http://www.german-autobahn.eu/index.asp?page=construction

[bassoon1986]

Alternate I-10 shields are posted along US 190 in south Louisiana for relief from the I-10 Atchafalaya Basin Bridge. Some of the "Alternate" banners are blue to match the shield, but some are white. They each have "xx miles" beneath to show the distance back to I-10 which is very helpful. Also on I-49 between US 190 and I-10 the alternate I-10 is shown on a LGS

[Henry]

And technically speaking, isn't I-670 in Kansas City also signed as Alternate I-70?  I seem to recall that being true once.  The one definitive thing I can say about that is that it is the shorter route.

Yeah. In Ohio, there are Alt I-70 shields that I can only assume are detours from the interstate if it is backed up or closed.


iPhone

Well then, on that note, maybe the NJ Turnpike should be signed as ALT I-95 for those who wish to avoid Philadelphia.

[bing101]

Considering that both the Interstate and U.S. route systems have business routes, how come the Interstate Highway System doesn't have an official "Alternate" designation like the U.S. route system?

Perhaps if there were such a designation, just as Business Interstates are signed with green shields, Alternate Interstates could be signed with either brown shields, or all red shields.

In California if an interstate needs to be closed or renovated in Some cases it will say "Detour" in Orange and interstate shield is colored orange in some cases. Please check with your state.

[hbelkins]

In my view, the problem with "alternate"  (of any kind, including US or state routes) is that "ALT"  is a vague descriptor. Motorists would probably assume the alternate route is not the preferred route, but even if it's not preferred, is it a reasonable substitute, or is it a stopgap that's really intended for emergency use only? Is it a way to avoid traffic backups on the congested main route, or is it a scenic option for Sunday sightseers?

At least banners like "truck" , "bypass" , and "business"  make it clear what purpose those routes serve in relation to the main road.

And then you have the issues with whether a route is signed as Alternate XX or XXA. For US 41, the route is signed "Alternate US 41" in Kentucky but "US 41A" in Tennessee.

In at least one case the signed alternate route is the better route. Between Jonesville and Abingdon, Va., Alternate US 58 is mostly four-lane. Only a couple of short stretches are two-lane roads. "Regular" US 58 is two lanes except for its overlaps with US 23 and I-81.

[SD Mapman]

Don't forget Nebraska and its long "Alternate I-80" route.

[TheStranger]

In California if an interstate needs to be closed or renovated in Some cases it will say "Detour" in Orange and interstate shield is colored orange in some cases. Please check with your state.

There IS some informal Alternate interstate signage in the Los Angeles area, but for extremely short distances:

http://goo.gl/maps/ZaRdj

[NE2]

This is one thing they do well on Germany's Autobahn system. Between every interchange (wherever possible, and they do their best to make it possible) there is a set of local roads designated with permanent signage that provides an alternate route between the interchanges, in case something blocks the main highway.

Here's some more info: http://www.german-autobahn.eu/index.asp?page=construction

Pennsylvania does this with colored detours.

[US71]

This is one thing they do well on Germany's Autobahn system. Between every interchange (wherever possible, and they do their best to make it possible) there is a set of local roads designated with permanent signage that provides an alternate route between the interchanges, in case something blocks the main highway.

Here's some more info: http://www.german-autobahn.eu/index.asp?page=construction

Pennsylvania does this with colored detours.

Baton Rouge has an "Emergency" Alternate I-10 that follows US 190.

[english si]

This is one thing they do well on Germany's Autobahn system. Between every interchange (wherever possible, and they do their best to make it possible) there is a set of local roads designated with permanent signage that provides an alternate route between the interchanges, in case something blocks the main highway.

Here's some more info: http://www.german-autobahn.eu/index.asp?page=construction

Pennsylvania does this with colored detours.

As does Great Britain with its various shapes.

[1995hoo]

Regarding the general principle of "alternate" Interstate routes, I'd always assumed the numbering system for three-digit routes was intended to serve that function to some degree. If you're approaching Jacksonville and you see the sign for I-295, you know that's an "alternate" to taking I-95 through the city, for example.

Usually when states in which I drive need to post an alternate route for an Interstate, they use either temporary signs (such as those trailer-type message boards) or signs appropriate for the reason the road is closed (such as orange signs for construction). I remember for many years there were orange signs all over the place in the Bay Ridge section of Brooklyn reading "ALT ROUTE TO [I-278 shield] EAST," but I don't remember what project was underway that necessitated them. Probably something to do with the Belt Parkway between Exit 2 and the road's end at the Gowanus, given that Exit 2 for Fourth Avenue was posted with the "ALT ROUTE" banner (indeed it covered up the exit arrow, so a second one was installed further up the sign, and the latter was not removed when the orange banner came down, yielding a weird-looking BGS with two exit arrows). My grandparents lived in Bay Ridge, so I used to see those signs every time we visited.

Steve Anderson has a picture of the weird two-arrow sign. The original arrow is the one on the bottom; it was covered by the orange "ALT ROUTE" banner for what seemed like several years:

[PHLBOS]

Along I-84 Eastbound in Cheshire, CT near Exit 27 (I-691), there is an ALT I-84 trailblazer signs pointing to the I-691 routing.

[Rover_0]

You know, I've always thought of suffixed Interstates as "Alternate Interstates," in a sense. The best example I can think of is I-15E (now I-215) in California, as it returns to I-15. Of course, I-80N [now I-84 (W)] and I-15W [now I-86 (W)] may have qualified, but I can understand why they may not.

The thing is that 3dis and the occasional business loop freeway connecting to their associated 2di are what I would consider alternate Interstates. I wouldn't have minded if there were more suffixed Interstates (like I-15E)  or even lettered spurs/loops (I-95A, I-95B, etc.)* around today IMO.

*IIRC this was one of the earliest plans for 3dis and even the Interstate system (think I-A, I-B, etc.), correct?

[texaskdog]

I think it's funny like when you're driving in Wisconsin they have "alternate 94" which is just US highway 51 running alongside it.  But it worked out well since there was a traffic jam (51 is two lanes).