How Much does it cost to replace an at-grade intersection with an overpass?

[kernals12]

I'm curious to know what part of it is the most expensive? Is it site preparation? Is it just the amount of concrete and steel needed?

[silverback1065]

Earthwork and the bridge quantities.

[kernals12]

Earthwork and the bridge quantities.

What's that?

[silverback1065]

Quantities are all things needed to build something. Think of it as the receipt when you design a project. You list all items needed to build something and how much of it you need. You use those quantities to estimate the cost of the project. In the case of your question it's the cost of all the dirt work and all the things needed to build a bridge that makes it expensive. Buying right of way (buying property) can also be very expensive.

[1995hoo]

I'd think there are lots of variables depending on location and project size that could mean the most expensive part will differ by project, sometimes quite significantly.

[silverback1065]

I'd think there are lots of variables depending on location and project size that could mean the most expensive part will differ by project, sometimes quite significantly.

Definitely true. Rural projects can be more expensive than you think simply because it costs a lot to haul materials out to the project

[kernals12]

Quantities are all things needed to build something. Think of it as the receipt when you design a project. You list all items needed to build something and how much of it you need. You use those quantities to estimate the cost of the project. In the case of your question it's the cost of all the dirt work and all the things needed to build a bridge that makes it expensive. Buying right of way (buying property) can also be very expensive.

Okay, what's so expensive about building a bridge?

[silverback1065]

Quantities are all things needed to build something. Think of it as the receipt when you design a project. You list all items needed to build something and how much of it you need. You use those quantities to estimate the cost of the project. In the case of your question it's the cost of all the dirt work and all the things needed to build a bridge that makes it expensive. Buying right of way (buying property) can also be very expensive.

Okay, what's so expensive about building a bridge?

Pile driving the supports, all the concrete, rebar, etc. I'm not a structural engineer but I do know all of that and more makes it pretty expensive.

[1995hoo]

Presumably it's not just building a bridge, either–if there's an existing intersection, most likely some level of access will be retained, and that's likely to require a wider right-of-way for the ramps, which in turn may require acquiring property (whether via eminent domain or some other means will vary). The cost of the property is a variable.

[kernals12]

Presumably it's not just building a bridge, either–if there's an existing intersection, most likely some level of access will be retained, and that's likely to require a wider right-of-way for the ramps, which in turn may require acquiring property (whether via eminent domain or some other means will vary). The cost of the property is a variable.

But what if the intersection currently has a bunch of left turn lanes taking up space?

[silverback1065]

Presumably it's not just building a bridge, either–if there's an existing intersection, most likely some level of access will be retained, and that's likely to require a wider right-of-way for the ramps, which in turn may require acquiring property (whether via eminent domain or some other means will vary). The cost of the property is a variable.

But what if the intersection currently has a bunch of left turn lanes taking up space?

What do you mean?

[1995hoo]

Presumably it's not just building a bridge, either–if there's an existing intersection, most likely some level of access will be retained, and that's likely to require a wider right-of-way for the ramps, which in turn may require acquiring property (whether via eminent domain or some other means will vary). The cost of the property is a variable.

But what if the intersection currently has a bunch of left turn lanes taking up space?

See boldfaced word.

[kernals12]

Presumably it's not just building a bridge, either–if there's an existing intersection, most likely some level of access will be retained, and that's likely to require a wider right-of-way for the ramps, which in turn may require acquiring property (whether via eminent domain or some other means will vary). The cost of the property is a variable.

But what if the intersection currently has a bunch of left turn lanes taking up space?

What do you mean?

With an overpass, the space taken up by the left turns can be repurposed.

[silverback1065]

Presumably it's not just building a bridge, either–if there's an existing intersection, most likely some level of access will be retained, and that's likely to require a wider right-of-way for the ramps, which in turn may require acquiring property (whether via eminent domain or some other means will vary). The cost of the property is a variable.

But what if the intersection currently has a bunch of left turn lanes taking up space?

What do you mean?

With an overpass, the space taken up by the left turns can be repurposed.

It depends on the geometry, it may not matter, it could be just enough room for the piers (the vertical structure in the middle of the bridge)

[kernals12]

Quantities are all things needed to build something. Think of it as the receipt when you design a project. You list all items needed to build something and how much of it you need. You use those quantities to estimate the cost of the project. In the case of your question it's the cost of all the dirt work and all the things needed to build a bridge that makes it expensive. Buying right of way (buying property) can also be very expensive.

Okay, what's so expensive about building a bridge?

Pile driving the supports, all the concrete, rebar, etc. I'm not a structural engineer but I do know all of that and more makes it pretty expensive.

Do you think that stronger lightweight materials in the future could make such bridges less expensive?

[Scott5114]

Not likely. Remember, bridges aren't the only things that use steel and concrete. They have to compete with other building projects for those resources, and generally that takes the form of the price going up.

Labor is a huge cost center, too. Engineers have specialized knowledge and are expensive to hire. Working on bridges is a dangerous job, so you can't pay peanuts and expect to have anyone show up and build (remember, you have to compete for them too–if you can score a safe indoor job remodeling an office building that pays the same as the bridge project, who wants to build a stinkin' bridge?) And, of course one of the biggest cost sinks is going through the environmental approval process, which involves lawyers. None of these labor costs is ever going to go down.

[silverback1065]

Not likely. Remember, bridges aren't the only things that use steel and concrete. They have to compete with other building projects for those resources, and generally that takes the form of the price going up.

Labor is a huge cost center, too. Engineers have specialized knowledge and are expensive to hire. Working on bridges is a dangerous job, so you can't pay peanuts and expect to have anyone show up and build (remember, you have to compete for them too–if you can score a safe indoor job remodeling an office building that pays the same as the bridge project, who wants to build a stinkin' bridge?) And, of course one of the biggest cost sinks is going through the environmental approval process, which involves lawyers. None of these labor costs is ever going to go down.

the environmental process can take multiple years depending on the size of a job.

[jeffandnicole]

You also have to consider whats nearby. Businesses located in the corners of the intersection will lose some or all of their access to the existing roadways.

NJ is a high priced construction state, but to use one project as an example, converting 70/73 from a circle to an overpass cost about $50 million.

[jeffandnicole]

A few examples in Delaware:

The cost of this project is about $69 million:

https://www.capegazette.com/article/overpass-proposed-routes-113-and-404/198308

And this one was about $40 million:

https://www.delawarepublic.org/post/new-route-1-overpass-little-heaven-open-next-week

[kphoger]

I'm curious to know what part of it is the most expensive? Is it site preparation? Is it just the amount of concrete and steel needed?

By the way, are you only talking about grade separation, or are you talking about an interchange?  That is to say, an overpass does not imply access from one road to another.  Adding access ramps etc increases not only the amount of grading and concrete work, but also the amount of land acquisition.

[kernals12]

I'm curious to know what part of it is the most expensive? Is it site preparation? Is it just the amount of concrete and steel needed?

By the way, are you only talking about grade separation, or are you talking about an interchange? That is to say, an overpass does not imply access from one road to another.  Adding access ramps etc increases not only the amount of grading and concrete work, but also the amount of land acquisition.

I'm talking about a diamond interchange.

[lepidopteran]

If one of the roads is significantly below grade, that is one road "tunnels" under the other, you need a pumping system to prevent flooding.

And with the additional pavement required by the diamond interchange, many areas might require construction of an adjacent pond or some other form of stormwater mitigation. A good thing, IMHO.

[silverback1065]

If one of the roads is significantly below grade, that is one road "tunnels" under the other, you need a pumping system to prevent flooding.

And with the additional pavement required by the diamond interchange, many areas might require construction of an adjacent pond or some other form of stormwater mitigation. A good thing, IMHO.

This is something that is studied on every project and can increase the cost a lot! SR 37 in Fishers, IN had an over 1 million dollar cost increase due to drainage changes. Also a rule 5 permit is required and that is drainage related.

[kernals12]

If one of the roads is significantly below grade, that is one road "tunnels" under the other, you need a pumping system to prevent flooding.

And with the additional pavement required by the diamond interchange, many areas might require construction of an adjacent pond or some other form of stormwater mitigation. A good thing, IMHO.

This is something that is studied on every project and can increase the cost a lot! SR 37 in Fishers, IN had an over 1 million dollar cost increase due to drainage changes. Also a rule 5 permit is required and that is drainage related.

Most grade separation projects cost tens of millions so an extra 1 million for drainage isn't that big of a deal.

[silverback1065]

If one of the roads is significantly below grade, that is one road "tunnels" under the other, you need a pumping system to prevent flooding.

And with the additional pavement required by the diamond interchange, many areas might require construction of an adjacent pond or some other form of stormwater mitigation. A good thing, IMHO.

This is something that is studied on every project and can increase the cost a lot! SR 37 in Fishers, IN had an over 1 million dollar cost increase due to drainage changes. Also a rule 5 permit is required and that is drainage related.

Most grade separation projects cost tens of millions so an extra 1 million for drainage isn't that big of a deal.

It is when that increase happens after construction starts. [emoji15]