3D road design: Cutting costs without cutting corners

Although the benefits of computer-assisted design (CAD) and 3D modelling are well-established, they are perhaps better known for making life easier for designers and contractors than for their potential to economise projects for their clients.

But, as design software becomes more powerful and intuitive, project managers are discovering its capacity to revolutionise design communication and construction efficiency can have major implications for a project’s time and costs.

Indiana-based engineering firm Beam, Longest & Neff (BLN) provided a perfect example of efficiency achieved through software on its recently completed redesign of a major interchange between Interstate 69 and State Road 61/56 in Pike County in Indiana, US. BLN proposed a cost-reducing redesign of a new interchange project that would replace its original diamond design with a new design that would have SR 61/56 pass over I-69 rather than underneath it.

The fact BLN came onboard in the later stages of the project’s design phase in order to cut costs meant that keeping to a strict schedule was an absolute priority.

Using software packages from Bentley, including MicroStation, GEOPAK and LEAP CONSPAN, the firm was able to complete the project in just 90 days, reducing the construction time by more than two months and saving $5.5m in construction costs. Just one change made by the company, for example, reduced the area requiring rammed aggregate piers by 99%.

For its work on the I-69 project, BLN won the award for Innovation in Roads at the 2011 Bentley ‘Be Inspired Awards’ in Amsterdam.

We talked to BLN project managers Vance Epple and Dan Gibson, along with INDOT’s I-69 operations director Elliott Sturgeon, about the project and the benefits CAD and 3D software brought to this major interchange redesign.

Chris Lo: You used Bentley software for the project – what was it about that software that suits a road resign project like this?

Dan Gibson: Well, it’s our primary CAD package now. The original designer of the project also used this software and it’s pretty seamless to bring stuff into it from other CAD packages.

The power of criteria writing is what interests us, then transitioning that into 3D models later. We don’t have to keep redesigning from the start, we just use stuff that we build. It’s a building block effect and it just speeds the process up.

CL: What role did design software play in saving time on the interchange?

Vance Epple: Once we got the original designer’s CAD files, we were able to utilise the actual alignments used for the original design, then we could take Dan’s preliminary profiles and attach those to the alignment files.

In just a matter of an hour or two, we had the original alignments in, we had Dan’s preliminary profiles, so we could start getting into the design.

We didn’t have to go back and manually input the information again. Dan had done all of this stuff with GEOPAK, so we were able to very quickly pull together original design information, supplement it with our redesign and very quickly start checking our profiles and making sure we were going to have our site distance and all the other elements that we need to check as designers.

CL: BLN’s redesign was proposed as a cost reduction initiative. How did software help minimise unnecessary expense?

VE: There were a lot of steps we had to go through to submit information to INDOT to show that our profiles and ditches and all the different design elements had to be reviewed.

We got expedited reviews by the INDOT reviewers to make sure they were comfortable with what we were providing. Once we got close to the end, we were able to take the cross-section information, create the 3D surfaces and provide those to the contractor.

The contractor was able to go in and take our finished surfaces, load that into their earthwork equipment and start doing their grading for the interchange. The redesign saved roughly $5.5m and I believe the contractor estimated that his construction time dropped by about two and a half months.

CL: How did the use of 3D modelling and CAD software change communication between BLN, the original design consultant and the construction contractor?

VE: It really helped. There was also bridge design going on at the same time – our bridge department had to design a new bridge.

They used a host of Bentley products too, software packages like RC-PIER and LEAP. They were able to work on their stuff and do their design and we had some of their files referenced into our files.

So whenever they made changes to the bridge, it was automatically updated in our files. We didn’t have to transfer files back and forth, when they updated their bridge information it automatically updated in our files. So it allowed us to work on guard-rails and drainage structures and all of our different elements, and have multiple people working at the same time.

DG: Without stepping too much on people’s toes.

VE: Yeah. We would design guard-rails on one file and drainage structures in another file, and the bridge has its own files. So we were able to have multiple people working at the same time without trying to figure out who was in what file.

We were able to have people working in different files and then reference everything into the plan-sheet. All the different pieces came together in the final product.

CL: Do you think creating a 3D model helps to better convey your designs to clients and stakeholders like INDOT?

DG: In terms of the 3D model, it really played the biggest role with the contractor. In the initial stages, we didn’t necessarily have the 3D model for INDOT, although that is something you could do in the future, especially if you have the public involved.

With the state of the economy these days, INDOT’s going to go at any opportunity to do more with less.

On this project, the 3D model was not really used as the selling tool until later on, it wasn’t really part of the initial decision to go ahead with the CRI, but afterwards it helped with the contractor.

CL: What would you like to see CAD and 3D modelling offer in the future to make road design or upgrade projects run even more smoothly?

DG: Besides a magical ‘design the road’ button, it should just become more robust, I think. Obviously, it takes a lot of time to do the 3D modelling.

We know that things are moving towards selling your designs to the public with public information displays, so it would really be nice if we could do 3D models with flythroughs and everything that you could sell the public on.

Instead of having to spend way too much time rendering, you could pull in existing video or pictures of the areas that merge with the model.

VE: As the software becomes more powerful, it’ll make it a lot easier for us to do this type of rendering and show some 3D models.

It’s been done for a long time, there are some pretty impressive displays that we’ve seen, but they’ve probably been rather labour-intensive. So some more automation would be good.

Elliott Sturgeon: I’d like to add something from the customer side. We’ve not seen a lot of 3D modelling on any of our jobs.

I know we had an intersection down in Evansville that we built according to 2D plans and when we got done the side slopes on a couple of driveways were almost unusable.

I think if we’d had 3D modelling on that, the problem would have been really evident – we ended up having to go back and re-do some of the pavements and some of the grades.

I’m not in the position to say we should be using 3D models, but I think it would be an excellent tool for the customer to see what they’re getting, to look at the critical points – the interchanges and bridge structures – to see how they fit together.