AARoads Forum

Please login or register.

Login with username, password and session length
Advanced search  

News:

The AARoads Wiki is live! Come check it out!

Author Topic: Over to under  (Read 1201 times)

roadman65

  • *
  • Offline Offline

  • Posts: 15887
  • Location: Lakeland, Florida
  • Last Login: Today at 01:45:43 AM
Over to under
« on: April 18, 2022, 07:56:46 AM »

I was noticing that in Texas on two major interstate widening projects, that some overpasses between Beaumont and Winnie are being removed and replaced with underpasses. What difference does it make whether the crossroad passes over or under?

Then I saw on I-45 south of Webster and the mall along the south feeder road with a surviving Sears store still left, that two ramps in the median were being constructed until I saw the widths of them. I then quickly concluded that they were not HOT entrances and exits, but the freeway itself being raised to the height of the crossroad.  Of course it’s not a raised at grade, but the freeway and crossroad are being switched out.

Seems like TxDOT entered the Twilight Zone lately.  In addition NJDOT did a switch as well at the US 1 and 9 split in Woodbridge.  US 9 south used to cross over US 1 north and now the position changed since 2002 during a bridge replacement need ( as the US 9 overpass was built in the 1030s and outlived its service life).   Though I think that decision was made for convenience as more footwork and detours would have been needed to construct a parallel replacement, however what is TxDOT doing these things for?

https://goo.gl/maps/ZoCCvwWPhLFDtoAL8
This is one of them. The overpass in the caption is presently demolished and I-10 is being raised up over the meeting place of the two roads. The service roads, though, are not. So now we are going to have the Service road and Smith Road meet at grade which also was grade separated since the day I-1o got built.
« Last Edit: April 18, 2022, 08:10:52 AM by roadman65 »
Logged
Every day is a winding road, you just got to get used to it.

Sheryl Crowe

jdbx

  • *
  • Offline Offline

  • Posts: 258
  • Location: Pleasant Hill, CA
  • Last Login: March 18, 2024, 02:09:02 PM
Re: Over to under
« Reply #1 on: April 18, 2022, 02:20:06 PM »

I was noticing that in Texas on two major interstate widening projects, that some overpasses between Beaumont and Winnie are being removed and replaced with underpasses. What difference does it make whether the crossroad passes over or under?

Then I saw on I-45 south of Webster and the mall along the south feeder road with a surviving Sears store still left, that two ramps in the median were being constructed until I saw the widths of them. I then quickly concluded that they were not HOT entrances and exits, but the freeway itself being raised to the height of the crossroad.  Of course it’s not a raised at grade, but the freeway and crossroad are being switched out.

Seems like TxDOT entered the Twilight Zone lately.  In addition NJDOT did a switch as well at the US 1 and 9 split in Woodbridge.  US 9 south used to cross over US 1 north and now the position changed since 2002 during a bridge replacement need ( as the US 9 overpass was built in the 1030s and outlived its service life).   Though I think that decision was made for convenience as more footwork and detours would have been needed to construct a parallel replacement, however what is TxDOT doing these things for?

https://goo.gl/maps/ZoCCvwWPhLFDtoAL8
This is one of them. The overpass in the caption is presently demolished and I-10 is being raised up over the meeting place of the two roads. The service roads, though, are not. So now we are going to have the Service road and Smith Road meet at grade which also was grade separated since the day I-1o got built.

The only reason I can think of, without knowing any background, is that this is to get around the issue of low-clearance bridges.  In the street view you shared, that appeared to be a sub-standard clearance.  In my area, CalTrans has been doing a lot of work on I-80 recently to raise bridges to eliminate the sub-standard clearances.  In our case, they are simply raising the bridges (some cases by rebuilding, other cases by jacking the deck up and building taller support columns) but maybe Texas has a different strategy?
Logged

HighwayStar

  • *
  • Offline Offline

  • Posts: 1523
  • Location: Lilliput
  • Last Login: November 06, 2023, 10:56:26 AM
Re: Over to under
« Reply #2 on: April 18, 2022, 02:32:34 PM »

The freeway going over solves a few issues.

One is low clearance bridges, for mega loads etc. this is the superior option. And this is likely what they have in mind designing them as such.
Another is pedestrian facilities, if you put the local road over the top it needs sidewalks for pedestrians, the freeway does not need that.
Another benefit is the removal of a location where debris can fall onto (or be thrown onto) the freeway. 

One downside however is related to those instances where the overpass/underpass serves as an interchange as well. When the freeway is under, the off ramp goes uphill and the on ramp goes downhill, which is the ideal configuration for aiding vehicles in speeding up or slowing down.
When you make the freeway the top that is reversed.
Logged
There are those who travel, and those who travel well

kphoger

  • *
  • Offline Offline

  • Posts: 29128
  • My 2 Achilles' heels: sarcasm & snark

  • Location: Wichita, KS
  • Last Login: March 18, 2024, 09:31:10 PM
Re: Over to under
« Reply #3 on: April 18, 2022, 02:50:15 PM »

In the street view you shared, that appeared to be a sub-standard clearance.

15'7" specifically, on both frontage roads.
Logged
Keep right except to pass.  Yes.  You.
Visit scenic Orleans County, NY!
Male pronouns, please.

Quote from: Philip K. Dick
If you can control the meaning of words, you can control the people who must use them.

skluth

  • *
  • Offline Offline

  • Posts: 3250
  • Age: 67
  • Location: Palm Springs, CA
  • Last Login: February 20, 2024, 03:35:22 PM
Re: Over to under
« Reply #4 on: April 18, 2022, 03:48:53 PM »

A factor to change the configuration from over to under is what may be cheaper. I looked at some Google Earth historic imagery at the South Major Drive interchange to the east and it looks like the new configuration has significantly shrunk the interchange footprint as the EB frontage road no longer goes under South Major Drive which required a connector road . The old WB frontage road connected to South Major 600' north of the highway. There are still traces of the old footprint including that construction staging area SE of the interchange. I'm guessing the new interchange at Smith Road will be a similar configuration where the frontage roads will directly intersect Smith Road like at Major Drive. Along with reducing the interchange footprint, moving Smith Road under I-10 will mean two short I-10 bridges across Smith Road instead of one Smith Road bridge with a 230' span across I-10 and two frontage roads.
Logged

Big John

  • *
  • Offline Offline

  • Posts: 4535
  • Age: 56
  • Last Login: Today at 02:23:52 AM
Re: Over to under
« Reply #5 on: April 18, 2022, 04:34:44 PM »

The freeway going over solves a few issues.

One downside however is related to those instances where the overpass/underpass serves as an interchange as well. When the freeway is under, the off ramp goes uphill and the on ramp goes downhill, which is the ideal configuration for aiding vehicles in speeding up or slowing down.
When you make the freeway the top that is reversed.
WisDOT has a policy of preferring the cross road to go over the freeway at interchanges for this reason.
Logged

SEWIGuy

  • *
  • *
  • Offline Offline

  • Posts: 4070
  • Grid Anarchist

  • Last Login: March 18, 2024, 08:05:19 PM
Re: Over to under
« Reply #6 on: April 18, 2022, 04:43:41 PM »

The freeway going over solves a few issues.

One downside however is related to those instances where the overpass/underpass serves as an interchange as well. When the freeway is under, the off ramp goes uphill and the on ramp goes downhill, which is the ideal configuration for aiding vehicles in speeding up or slowing down.
When you make the freeway the top that is reversed.
WisDOT has a policy of preferring the cross road to go over the freeway at interchanges for this reason.


Is that still the case?  For instance, the majority of the new-ish interchanges (9 out of 12 if I have it right) on WI-26 between Janesville to north of Watertown have the highway running over the cross street.
Logged

Brian556

  • *
  • *
  • Offline Offline

  • Posts: 2419
  • Location: Lewisville, TX
  • Last Login: March 18, 2024, 11:18:44 PM
Re: Over to under
« Reply #7 on: April 18, 2022, 08:47:48 PM »

On I-35E between Dallas and Denton, when it was recently redone, FM 407 and Corinth Pkwy were changed from over to under. At FM 407, it made more sense for it to be on the lower level, because that would allow for a normal interchange vs the oddball design that was there before. At Corinth Pkwy, changing Corinth Pkwy to be on the lower level allowed the frontage roads to be straight instead of bowing out like they did before, and also avoided having a steep hill east of the crossing to get down to the level of the DCTA RR crossing. Historical Note: When I-35E was constructed, the MKT RR was still active, but Corinth Pkwy did not yet exist. The MKT was taken out of service in 1977, and pulled around 1992. Corith Pkwy was built in recent times, before the DCTA line was built on the former MKT grade. When the DCTA lien was constructed, a pedestrian tunnel for the rail trail on the former MKT grade was removed, and Corinth Pkwy was brought down to ground level to accommodate DCTA. This created a somewhat steep hill on Corinth Pkwy E of I-35E.
Logged

 


Opinions expressed here on belong solely to the poster and do not represent or reflect the opinions or beliefs of AARoads, its creators and/or associates.