Elevation difference between Interstate lanes

[mightyace]

In Distance between Interstate lanes, we talked about horizontal separation between interstate lanes.

How about situations where there is a significant elevation (vertical) difference between the lanes.

Now, small amount (less than 20 feet) happen often for many reasons including interchanges.

I'm interested in larger differences that aren't part of an interchange.

Many interstates in mountainous territory have such differences like I-80 in PA, I-81 in TN, VA or PA, I-70 in Glenwood Canyon, CO.

Another example, is the Ohio Turnpike climbing out of the Cuyahoga River Valley on the west side.  The WB lanes are significantly lower than the EB lanes.  It is great enough that when I-271 crosses the turnpike, it goes under EB 80 and over WB 80!

http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=boston+heights+oh&sll=37.0625,-95.677068&sspn=32.527387,79.013672&ie=UTF8&hq=&hnear=Boston+Heights,+Summit,+Ohio&ll=41.252774,-81.583786&spn=0.007534,0.01929&t=h&z=16&layer=c&cbll=41.252804,-81.584065&panoid=7LbIC7Vx2J7shcjOu5MbWw&cbp=12,252.83,,0,5

[Chris]

I-70 in western Colorado

[mightyace]

^^^
That's Glenwood Canyon that I was referring to.  Thanks for the picture.

I have some non-digital pictures of that highway taken from the railroad on the other side of the canyon when I rode the California Zephyr in 1998.

[Revive 755]

The two double deck sections on I-64 in St. Louis.  The eastern section with a smaller vertical distance (note that when this section was built, most of the parking lots below were part of the railyards to the south).
http://maps.google.com/maps?hl=en&ie=UTF8&ll=38.622566,-90.19939&spn=0,359.993134&t=k&z=18&layer=c&cbll=38.623386,-90.201527&panoid=HUPUDRwFzELEJX-tpX5OmA&cbp=12,99.24,,0,1.7

The western section with the larger vertical distance:
http://maps.google.com/maps?hl=en&ie=UTF8&ll=38.63169,-90.237279&spn=0,359.993134&t=k&z=18&layer=c&cbll=38.63192,-90.236993&panoid=ijE4p4gp_Qh0ASlugPTO2Q&cbp=12,118.04,,0,3.52

There's a section on I-55 near the I-270/255 interchange where the NB lanes run higher than the SB lanes.  I'm not sure why this section was built like this - all of the I-170 extension plans I've seen had the interchange at least 3/4 a mile or more north of here.
http://maps.google.com/maps?hl=en&ie=UTF8&ll=38.526883,-90.308647&spn=0,359.890137&z=14&layer=c&cbll=38.519661,-90.330911&panoid=4n1jkLVC4LtZ7qlbx5gEQg&cbp=12,216.74,,0,-0.98

I-44 has a couple sections where one side is higher.  Here's one near St. Robert:
http://maps.google.com/maps?hl=en&ie=UTF8&ll=37.802731,-92.188168&spn=0,359.780273&z=13&layer=c&cbll=37.81762,-92.188039&panoid=2IOv60sR51hLFJkbY7VDUg&cbp=12,70.49,,0,-0.48

Used to be a decent vertical separation on I-44 between the Lewis Road and Antire Road interchanges in St. Louis County, but it was wiped out when I-44 was six-laned through there, and I can't find that section on the old aerial photos.

I-229 has a brief section due to a double deck design along the Missouri River:
http://maps.google.com/maps?hl=en&ie=UTF8&ll=39.759142,-94.857084&spn=0,359.986267&z=17&layer=c&cbll=39.7593,-94.857131&panoid=3SzH9ME5bRupyD1P7mj89Q&cbp=12,167.54,,0,2.12

Somewhat decent sized separation between the lanes of I-40 west of Knoxville, TN:
http://maps.google.com/maps?hl=en&ie=UTF8&ll=35.889745,-84.680343&spn=0,359.945068&z=15&layer=c&cbll=35.885195,-84.688505&panoid=a7syNnxzjIQm-0t-ZsnzEg&cbp=12,7.1,,0,5.28

[Bickendan]

I-5 in downtown Seattle. The express lanes are double decked with the northbound lanes, with the southbound lanes between the two.

[mightyace]

I-80 West of Milesburg:  You can see the remnants of a crossover ramp here.

http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=milesburg&sll=41.061362,-77.393789&sspn=0.046208,0.144196&ie=UTF8&hq=&hnear=Milesburg,+Centre,+Pennsylvania&ll=40.982069,-77.802&spn=0.023132,0.055747&t=p&z=15&layer=c&cbll=40.982235,-77.802355&panoid=DfjoMmVyx__c5qOpoZS7aA&cbp=12,344.39,,0,10.68

[xonhulu]

Many interstates in mountainous territory have such differences like I-80 in PA, I-81 in TN, VA or PA, I-70 in Glenwood Canyon, CO.

Just throwing one out there, the two lanes of I-5 by Lake Shasta in California seem to be separated by an elevation difference of 380 ft, according to elevations given on Google Earth.  I won't be surprised if there are greater differences elsewhere.

This is a little hard to define, as how do you judge which points on each carriageway correspond?  I can get a 525-foot difference on I-84's Cabbage Hill grade if I pick the right points.

[mightyace]

Just throwing one out there, the two lanes of I-5 by Lake Shasta in California seem to be separated by an elevation difference of 380 ft, according to elevations given on Google Earth.  I won't be surprised if there are greater differences elsewhere.

This is a little hard to define, as how do you judge the points on each carriageway correspond?  I can get a 525-foot difference on I-84's Cabbage Hill grade if I pick the right points.

Well, a good approximation works for me as long as the two points are at approximately the same "mile marker."  This is true with horizontal separation as well.

But, you certainly beat any of my expectations.    I don't think any of the ones that I mentioned exceed 100 ft.

[TheStranger]

At Cajon Pass (which I traversed last Saturday), there's a difference of about 400 feet between northbound and southbound lanes on I-15:

http://maps.google.com/maps?f=q&source=s_q&hl=en&q=Cajon+Summit,+Wrightwood,+San+Bernardino,+California+92397&sll=37.0625,-95.677068&sspn=35.219929,54.84375&ie=UTF8&cd=1&geocode=FYYhDAId2uj_-A&split=0&hq=&hnear=Cajon+Summit,+Wrightwood,+San+Bernardino,+California+92397&ll=34.339928,-117.463374&spn=0.01793,0.026779&t=p&z=15

[xonhulu]

Well, a good approximation works for me as long as the two points are at approximately the same "mile marker."  This is true with horizontal separation as well.

But, you certainly beat any of my expectations.    I don't think any of the ones that I mentioned exceed 100 ft.

Now your response jogged my mind to another good question (which I probably should spin off into a new thread): how do mile markers correspond if the two carriageways go different distances?

So back to I-84, Cabbage Hill on Google Earth: using the Path function, I measured both the westbound (downhill) lanes and the eastbound (uphill) lanes between their splits.  The results: the WB lanes take about 6.4 miles going down, while the EB lanes take 7.1 miles going up.  Not surprising, as you'd prefer a slighter grade on the climbing lanes.  While this is not a huge difference, it begs the question: how are the mile markers measured through here when there's a .7 mile difference?  Do they pick one lane or the other, do they average them, or do they base it on some other imaginary "centerline" distance?  Anyone?

[Scott5114]

Now your response jogged my mind to another good question (which I probably should spin off into a new thread): how do mile markers correspond if the two carriageways go different distances?

That's probably where all the fun of milepost equations comes into play.

[andytom]

So back to I-84, Cabbage Hill on Google Earth: using the Path function, I measured both the westbound (downhill) lanes and the eastbound (uphill) lanes between their splits.  The results: the WB lanes take about 6.4 miles going down, while the EB lanes take 7.1 miles going up.  Not surprising, as you'd prefer a slighter grade on the climbing lanes.  While this is not a huge difference, it begs the question: how are the mile markers measured through here when there's a .7 mile difference?  Do they pick one lane or the other, do they average them, or do they base it on some other imaginary "centerline" distance?  Anyone?

ODOT keeps a road inventory on each roadway of a dual carriageway.  In this case, roadway 2 (presumably the WB one) has a gap equation (one for a shorter roadway) of .65 miles at the top of the hill, just east of exit 224, that roadway 1 doesn't have.

--Andy

[hbelkins]

There's a pretty significant elevation distance between the lanes of I-77 at Fancy Gap in Virginia.

Also a stretch of I-64 and I-77 in Charleston, WV.

[Alps]

Now your response jogged my mind to another good question (which I probably should spin off into a new thread): how do mile markers correspond if the two carriageways go different distances?

That's probably where all the fun of milepost equations comes into play.

Reminds me of a trip note I forgot.  Because I-40 was routed around I-240 in Memphis as a last-minute change, there are two sets of A/B mileposts.  For example, after 0.9 comes 1A.0 and after 1A.9 comes 1B.0, and only after 1B.9 do you get to 2.  That's a very rough and dirty way of equating mileposts.

[roadfro]

Now your response jogged my mind to another good question (which I probably should spin off into a new thread): how do mile markers correspond if the two carriageways go different distances?

So back to I-84, Cabbage Hill on Google Earth: using the Path function, I measured both the westbound (downhill) lanes and the eastbound (uphill) lanes between their splits.  The results: the WB lanes take about 6.4 miles going down, while the EB lanes take 7.1 miles going up.  Not surprising, as you'd prefer a slighter grade on the climbing lanes.  While this is not a huge difference, it begs the question: how are the mile markers measured through here when there's a .7 mile difference?  Do they pick one lane or the other, do they average them, or do they base it on some other imaginary "centerline" distance?  Anyone?

As far as FHWA is concerned, I believe official distance on Interstates is measured based on cumulative mileage on the eastbound or northbound carriageway, or  the direction of increasing mileposts.

For state bookkeeping, it depends on the agency.  Some agencies will use an imaginary "centerline" between the two sides, basing the mileposts in each direction on relative position of the centerline.  Other agencies will designate a primary direction that maintains the "official" mileage for the route, with the opposite direction containing secondary mileage--the secondary mileage may contain either a milepost gap or equation, or might have its own independent mileage record.  There may be other methods of mileposting such splits, but I believe these are the two most common.

[Duke87]

As far as FHWA is concerned, I believe official distance on Interstates is measured based on cumulative mileage on the eastbound or northbound carriageway, or  the direction of increasing mileposts.

That's definitely how New York does it.

[Mr_Northside]

I'll mention I-70 in PA just south of the Town Hill exit. (In between Breezewood & Maryland)

http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=milesburg&sll=41.061362,-77.393789&sspn=0.046208,0.144196&ie=UTF8&hq=&hnear=Milesburg,+Centre,+Pennsylvania&t=k&layer=c&cbll=39.878703,-78.24662&panoid=Mr3JkF8t7JO1c4InzhULeA&cbp=12,268.51,,0,-11.52&ll=39.881009,-78.244457&spn=0.005895,0.013733&z=17