Something weird that I've noticed in Illinois

[Gnutella]

I just got back from a road trip to St. Louis, and I've noticed that many Interstates in Illinois either don't get resurfaced under the overpasses, or they use concrete under the overpasses that isn't laid very well compared to the asphalt. Has anybody else noticed this? I've noticed it in a couple of places in Missouri, but it's mostly an Illinois phenomenon.

[SSOWorld]

They've done this in Wisconsin (I-39 had them prominently in the past and other freeways may have or used to have these).  I have no idea what the reason for it is - but I think it has something to do with the height of the bridge above the road.

[JREwing78]

Yep. Cheaper to overlay the existing pavement, but they have to create enough clearance under bridges to accommodate heavy truck traffic. It's very common in Michigan, though frequently they will tear out the original roadbed right under the bridge in order to create the clearance needed.

You'll notice that the pavement dips approaching an underpass, and rises up again after you clear it.

[Revive 755]

I just got back from a road trip to St. Louis, and I've noticed that many Interstates in Illinois either don't get resurfaced under the overpasses, or they use concrete under the overpasses that isn't laid very well compared to the asphalt. Has anybody else noticed this? I've noticed it in a couple of places in Missouri, but it's mostly an Illinois phenomenon.

It's very common in Indiana as well.

[cl94]

Indiana and Illinois seem to do that quite a bit, Indiana more so than Illinois. Then again, the bridges in the aforementioned states tend to be lower than elsewhere.

[GaryV]

Often an overpass won't be repaved.  I'm guessing that's for weight.

[peterj920]

Often an overpass won't be repaved.  I'm guessing that's for weight.

Wisconsin repaves their overpasses quite frequently.  For a cheap fix, they will overlay with asphalt.  Once the asphalt on the deck wears out, then the bridge deck is replaced with new concrete.  The Leo Frigo Bridge was just recently asphalt overlaid, the Hoan Bridge, High Rise, and Wis 172 were recently redecked, but received an asphalt overlay prior to that.  When I traveled to Ontario, every overpass I crossed had an asphalt overlay, was interesting not seeing a single concrete deck from Windsor to Niagara Falls.  Ontario 407 is the only concrete surface I encountered in all of Ontario.  It may be because it's owned by a private company.  The bridge decks were the exception and every bridge deck had an asphalt overlay. 

[codyg1985]

By contrast, Alabama will jack up the bridge superstructure so that the additional pavement layer can be added.

[Gnutella]

The clearance aspect makes sense, though I would say that Illinois, Indiana and the other Midwestern states that do this probably ought to start replacing the overpasses eventually. Isn't 16'6" the new standard anyway? (The old standard was 14'0", right?)

[Big John]

http://safety.fhwa.dot.gov/geometric/pubs/mitigationstrategies/chapter3/3_verticalclearance.cfm

16' vertical clearance for interstates is the usual standard, but can be as low as 14' if there is another interstate in the area that meets the 16' standard.  http://safety.fhwa.dot.gov/geometric/pubs/mitigationstrategies/chapter3/3_verticalclearance.cfm

[Moose]

I seem to remember 5 or so years back, they undercut a lot of the underpasses to increase clearance. I know some of them have a noticeable dip to them.

[theline]

Along the older portion of the St. Joseph Valley Parkway near South Bend, constructed in the late '50s or early '60s, INDOT lowered the road under the SR-23 bridge recently to increase clearance to meet current standards. They chose to replace the Locust Road and Ireland Road bridges for the same reason. I'm not sure of the reason for the different approaches.

[Rick Powell]

http://safety.fhwa.dot.gov/geometric/pubs/mitigationstrategies/chapter3/3_verticalclearance.cfm

16' vertical clearance for interstates is the usual standard, but can be as low as 14' if there is another interstate in the area that meets the 16' standard.  http://safety.fhwa.dot.gov/geometric/pubs/mitigationstrategies/chapter3/3_verticalclearance.cfm

It depends on the Department of Defense STRAHNET clearances.  In the Chicago area, vertical clearances are allowed to be under 16 feet inside of the I-294 beltway.