Why is double-decker construction frowned upon?

[noelbotevera]

Thread title says it all. I'm not sure why this practice is a little bit more common.

I thought about pros and cons about double-decker highways.

Pros:

• Cheaper to construct, as it requires placing a roadbed on top of something instead of having to clear land.
• Easier to construct, as more ROW is not required.
• More lanes can easily be added without using more ROW

Cons:

• Visual headache, unless any landscaping or artwork is installed
• Harder to construct interchanges (however, it could be like a local express system)
• Narrow shoulders, and little to no space for breakdowns

Thoughts?

[1995hoo]

Major expense of building the upper level and the ramps. Definitely not cheaper in most places regardless of ROW issues.

[Max Rockatansky]

Pretty hard to expand double decker freeways due to the way they are designed. 

[noelbotevera]

Major expense of building the upper level and the ramps. Definitely not cheaper in most places regardless of ROW issues.

Right, I forgot about ramp construction to the upper level.

Pretty hard to expand double decker freeways due to the way they are designed. 

Didn't this happen to I-10/I-35 in San Antonio? I believe it was expanded a couple years ago.

[cl94]

Major expense of building the upper level and the ramps. Definitely not cheaper in most places regardless of ROW issues.

This. It is typically done only in the case of long bridges/tunnels and extremely limited/expensive ROW. Of the non-bridges/tunnels that have two decks, the LIE just east of the BQE in Queens has C/D roads underneath to minimize the number of graves that needed to be moved when it was plowed through a cemetery. The mess on I-84/CT 8 in Waterbury is likely multiple levels due to terrain.

For bridges, the reason for adding a second deck instead of a wider bridge should be pretty self-explanatory: cheaper to double capacity by double-decking than by making it twice as wide.

Didn't this happen to I-10/I-35 in San Antonio? I believe it was expanded a couple years ago.

Different design. These are "terraced", in that one level is not directly above the other. Subtle difference, I know, but has a bit of impact. Typical double-deck freeway has travel lanes stacked, so supports have to go just outside the shoulders.

[Max Rockatansky]

Major expense of building the upper level and the ramps. Definitely not cheaper in most places regardless of ROW issues.

Right, I forgot about ramp construction to the upper level.

Pretty hard to expand double decker freeways due to the way they are designed. 

Didn't this happen to I-10/I-35 in San Antonio? I believe it was expanded a couple years ago.

Pretty sure you're right, doesn't mean it was cheap.    I was thinking more along the lines of the demise of the Embarcedero Freeway.

[jeffandnicole]

Overpass expenses are extremely high.  A simple overpass over a roadway can cost at least $5 million.  The PA Turnpike is reconstructing an overpass in Bensalem where the cheapest bid was $21 Million.  The overpass is only about 120 feet long. 

ROW generally is pretty cheap, especially in rural areas.  In areas where it's more expensive, the property owners that don't want to lose ROW for a widened highway also don't want a visually unpleasing double decker highway across the street from their front yard either.

Noise would be another issue, and in suburban/urban areas, sound walls would almost be a necessity, further increasing the cost.

[nexus73]

Two words come to my mind: Loma Prieta.

Rick

[noelbotevera]

Two words come to my mind: Loma Prieta.

Rick

.....ah.

[myosh_tino]

Two words come to my mind: Loma Prieta.

Rick

.....ah.

Double-deck freeways are definitely not recommended in earthquake country.

For those that don't know, the double-decked Cypress Structure (I-880) in Oakland collapsed when the Loma Prieta earthquake struck the San Francisco Bay Area in 1989 killing 42.

[jeffandnicole]

But...that was also using older construction techniques. We might as well ban any building over 1 story tall as well.

[hobsini2]

I got no problem double decking a freeway when the freeway has been expanded to its capacity. I seem to recall that Minnesota did an express lanes over 394 that is a toll road with access to only a few interchanges. Been so long since I was up there I have forgotten.

But doing a full blown double decking could work in congested areas. For example, I do think double decking the Eisenhower in Chicagoland from 1st Ave to Ashland Ave would ease the congestion on the west end. The bitch would be trying to figure out from Ashland east to the Circle.

[cl94]

I got no problem double decking a freeway when the freeway has been expanded to its capacity. I seem to recall that Minnesota did an express lanes over 394 that is a toll road with access to only a few interchanges. Been so long since I was up there I have forgotten.

But doing a full blown double decking could work in congested areas. For example, I do think double decking the Eisenhower in Chicagoland from 1st Ave to Ashland Ave would ease the congestion on the west end. The bitch would be trying to figure out from Ashland east to the Circle.

This. I think a double-decking would be great along I-190 north of the Peace Bridge in Buffalo to make it 6 lanes. For those unfamiliar, ROW constrains it to 4 lanes. Problem is fitting it around a couple of bridges.

[Revive 755]

Two cons I don't seen mentioned yet:

1) Icing on the upper roadway in winter:  I seem to recall that the double decked sections of US 40 in St. Louis usually started having accidents and/or slow downs in winter weather before any of the other interstates.

2) Maintenance:  Usually more with a bridge structure than a facility on ground or embankment, and becomes a much bigger headache when major repairs are needed.  There's a much greater chance that the whole facility may need to be closed for major repairs than with a side by side arrangement.  Missouri has had/is having this issue with the US 40 structures in St. Louis and the I-229 structure in St. Joseph.  The higher cost for repairs required for the structure on I-229 are likely to lead to its demise.

Two words come to my mind: Loma Prieta.

Seems like one only hears about the Embarcedero Freeway and the I-880 Cypress Structure from that earthquake - how did the double deck sections on US 101 and I-280 hold up?

Pretty hard to expand double decker freeways due to the way they are designed.

Missouri was (is?) going to add a third through lane on part of the double deck section of US 40 just west of the PSB, though it was going to be closer to a C-D lane in design than a through lane.
Google aerial of area

[DAL764]

Two words come to my mind: Loma Prieta.

Rick

.....ah.

Double-deck freeways are definitely not recommended in earthquake country.

Tell that to Japan. They have double-decker freeways all over the place in the large metropolitan areas, be it Tokyo, Osaka, or even Kobe, where the Great Hanshin Earthquake caused this to happen:
https://onionbaasan.files.wordpress.com/2012/01/01.jpg

Yet they still built more double-decker with newer, more stringent regulations.

[myosh_tino]

Two words come to my mind: Loma Prieta.

Seems like one only hears about the Embarcedero Freeway and the I-880 Cypress Structure from that earthquake - how did the double deck sections on US 101 and I-280 hold up?

The double-decked portion of US 101 was torn down around the same time as the Embarcadero Freeway.  The only double-decked structures left in the S.F. Bay Area are the I-280 extension between US 101 and Evans Ave and the Bay Bridge.

[TheStranger]

The double-decked portion of US 101 was torn down around the same time as the Embarcadero Freeway.

Something I've always wondered - was the Central Freeway north of Fell Street ever open after the 1989 earthquake (before its early-90s demolition)?

One of the decks from Van Ness Avenue west to Fell remained in operation until about 15 years ago, when that was demolished as part of the project to connect Octavia Boulevard with a new west end of the freeway.  Interestingly, the gentrification of Hayes Valley has made the remaining portion of the Central Freeway much more useful than before (as Octavia provides 4-5 access points to the restaurants and boutiques, where the old configuration only provided access points at Fell/Laguna).

The only double-decked structures left in the S.F. Bay Area are the I-280 extension between US 101 and Evans Ave and the Bay Bridge.

Isn't the Richmond Bridge double-deck too?

The Bay Bridge's double-deck portion has been a bit shorter now that the new east half of the bridge has been in operation a couple of years.

[Revive 755]

Isn't the Richmond Bridge double-deck too?

Yes

Another con:  Difficulty with first constructing the double deck arrangement if on an existing facility.  I recall an old newspaper article indicating a double deck arrangement for I-55 between the PSB and I-44 in St. Louis was not favored due to having to close I-55 for a year to build it.

[J N Winkler]

Seems like one only hears about the Embarcedero Freeway and the I-880 Cypress Structure from that earthquake - how did the double deck sections on US 101 and I-280 hold up?

US 101 and I-280 had relatively few problems because, rather unusually for freeway bridges in general (not just in California), they have steel piers for some structures.  But the Central Freeway in San Francisco (freeway US 101 segment that never quite made it to the Bay Bridge) has been removed and converted to a boulevard, just like the Embarcadero.  Anything not actually removed that has concrete piers has been retrofitted to death with pier jackets to resist torsion.

The two freeway bridges that actually had collapsed segments in Loma Prieta were the Cypress Viaduct and the Bay Bridge east span.  The latter killed far fewer people (just one person), but was considered highly worrisome because further shaking would have brought down the entire east span like a house of cards.

[TheStranger]

But the Central Freeway in San Francisco (freeway US 101 segment that never quite made it to the Bay Bridge) has been removed and converted to a boulevard, just like the Embarcadero.

Only the portion from Market Street north to Fell Street became part of the expanded Octavia Boulevard (formerly Octavia Street) in Hayes Valley.  (The portion from Fell Street to Golden Gate Avenue was completely removed in 1991 and some of the right of way remains, but not all; the old offramp at Fell and Laguna is now a community garden)

The Central Freeway from Market Street to Van Ness Avenue is actually relatively new construction from 2005, replacing the old double-deck arrangement with a single-deck, four-lane dual carriageway that now ends at Market.  This is signed as an offramp to Octavia Boulevard, though it continues to be the mainline lanes heading west past Mission/Van Ness.

East of Van Ness Avenue, the portion of Central Freeway on that stretch is the original, 1950s-construction viaduct and still carries US 101 as it has for decades.

---

The double-deck section of the 280 extension was actually closed until 1994-1995 (CSAA maps of the time noted the closure, as well as 480's closure/removal) but has since for the most part been continuously open to traffic.

[michravera]

Thread title says it all. I'm not sure why this practice is a little bit more common.

I thought about pros and cons about double-decker highways.

Pros:

• Cheaper to construct, as it requires placing a roadbed on top of something instead of having to clear land.
• Easier to construct, as more ROW is not required.
• More lanes can easily be added without using more ROW

Cons:

• Visual headache, unless any landscaping or artwork is installed
• Harder to construct interchanges (however, it could be like a local express system)
• Narrow shoulders, and little to no space for breakdowns

Thoughts?

It is hard to make them wide enough to matter for a sufficient route length with sufficient clearance with a sufficient load and seismically safe at the same time. Remove any one of these constraints and you probably have a solution that has been tried.

Where you don't have to worry about seismicity (13 or so states in the US haven't had 3.0 or stronger events since European settlement) but do have right of way considerations, go for it.

When you can, for instance, ban trucks, busses, and motorhomes, on the lower deck so that you can get away with low clearances, go for it.

When you can double deck for just a couple of hundred meters, go for it.

When you can ban trucks from the upper deck and make the required load less, go for it.

When you can build a one- or two-lane carriageway, go for it.

But what is the point of a road that can't handle trucks, is only a lane or two wide, is just a couple hundred meters long, or will likely be the only place where people die in a minor earthquake? In short, we have a solution for a somewhat limited problem set.

[Buffaboy]

I got no problem double decking a freeway when the freeway has been expanded to its capacity. I seem to recall that Minnesota did an express lanes over 394 that is a toll road with access to only a few interchanges. Been so long since I was up there I have forgotten.

But doing a full blown double decking could work in congested areas. For example, I do think double decking the Eisenhower in Chicagoland from 1st Ave to Ashland Ave would ease the congestion on the west end. The bitch would be trying to figure out from Ashland east to the Circle.

This. I think a double-decking would be great along I-190 north of the Peace Bridge in Buffalo to make it 6 lanes. For those unfamiliar, ROW constrains it to 4 lanes. Problem is fitting it around a couple of bridges.

Great minds think alike, this immediately came to mind when I opened the thread.

[paulthemapguy]

Two words come to my mind: Loma Prieta.

Rick

.....ah.

Double-deck freeways are definitely not recommended in earthquake country.

For those that don't know, the double-decked Cypress Structure (I-880) in Oakland collapsed when the Loma Prieta earthquake struck the San Francisco Bay Area in 1989 killing 42.

That Loma Prieta comment caught me off guard too lol.  Oy vey.
The Alaskan Way comes to mind, through downtown Seattle.  That's a double-decker.  Double-decker roadways can be constructed with earthquake considerations, but I bet they're more expensive due to those additional considerations.  With that said, the Alaskan Way is important enough to Seattle for them to spend $(Elephant shitload) on a new extension and underground tunnel.  My point is, this supports the claim that double-decker freeways only exist where the local agency is willing to spend a TON of money on it.  (They're a result of opulence, which, like earthquakes, seems to be a west-coast trend)

[roadman65]

In San Antonio they did not frown upon widening I-10 and I-35 by building over the existing freeway.

Back to the subject, my dad used to say if NJDOT built the cancelled I-278 over the former SIRT freight line between Cranford and Linden they would have never had to destroy the many homes in Linden and Roselle to have at least built the freeway to the Garden State Parkway at least.  NJDOT should have considered having that freeway built like that as connecting the GSP to the Goethals Bridge would be most feasible being the Parkway is one of NJ's main freeways and the bridge is a vital link to Staten Island and Brooklyn.