Curious Iowa: What goes into planning a road?

Road construction season is upon us. While lane and road closures can be a headache for drivers, they’re necessary to fix roads and build new ones.

But what work goes into planning a new road? That’s what one person wondered when they wrote to Curious Iowa, a series from The Gazette that answers questions about Iowa, its culture and the people who live here.

The Gazette spoke with Hiawatha-based engineering firm Hall & Hall Engineers to find out what goes into planning a road.

How are residential roads planned out?

Loren Hoffman, private development team leader at Hall & Hall Engineers, said the first step in planning a road is concept development. Since Hoffman’s team works on private development, we framed our conversation around the development of a residential street extension.

In the concept development stage, the client tells Hoffman’s team their goals for the project. A drone is flown over the site to collect aerial imagery and a site inventory is taken.

“A site inventory is where we evaluate the existing conditions, opportunities, and constraints of the site,” Hoffman said. This includes gathering information on zoning, topography, traffic volumes and existing utilities. Plus, any contour data and property line information that’s available online.

“It’s not quite to the tolerances that you would want for a final design, but certainly within tolerances for a preliminary, like a master plan,” Hoffman said of the online data.

A lot of mathematical calculations are required to engineer a road. Hall & Hall Engineers traffic engineer Matt Johnson gave the example of drainage. In an urban section, drainage goes through a system of gutters, intakes and storm sewers.

“And that’s where we get into a lot of the math and the calculations of the project,” Johnson said. “The analyzing the amount of rainfall that’s coming down on this area and how much is draining to the street so we know how big of intakes to have, how frequently to place them and the how big of pipes to carry away from them and where to go with those things.”

  Buy Photo

During the concept development phase, the major pavement construction details are considered, like the number and width of lanes needed. Then concept plans for the street network are laid out to most efficiently use the land. Model plans are drafted using CAD software.

Hoffman said two to three people, plus the client and city, are involved in the early stages of the process, which can take anywhere from “two weeks to three to four months.” When that’s finished, the project goes through the preliminary plat process and rezoning.

“You’ll need to rezone the property to whatever use from industrial to residential to commercial, whatever that might be. Along with that is a preliminary plat that shows kind of where the streets will be extended, how the lots will lay out on the site,” Hoffman said. “And that process, the rezoning and the preliminary plat process again happens in a series of meetings through the city that ultimately culminates with, often, public hearings and meetings at city council.”

That process can take three to four months. In the final design stage, it is determined what road or lane closures are needed to complete the project. These closures actually expedite the construction process. When a roadway is built in pieces, it becomes more difficult to make everything line up and match.

"If I was looking specifically at a residential street, a lot of times what we’ll do is … keep half of the road open so that they can still get into their driveways while they’re building the other half,“ Johnson said. ”But that really slows the contractor down because he has very limited access to the site to be able to do his work. So a lot of times, it’s actually faster and less of an inconvenience if we can just shut the whole roadway down for a shorter period of time … and it usually ends up with a better end product also.“

The final plans and a cost estimate are handed off to the client who will give the plans to someone else to do the construction work. For public improvement projects, a bidding process is required by state law. This is when bids are solicited from contractors and the city council or board of supervisors “awards” a contract based on bids.

In addition to the plans, the engineering firm also creates a list, Hoffman said, that includes things like scraping off the topsoil and stockpiling it to the side and bringing in gravel rock that goes underneath the paving. Contractors review that list and submit what it would cost to do each component of the project.

“And then we tally that all up and that’s their overall bid for the project,” Hoffman said.

All of the bids are sealed and reviewed at the same time. Then the bids and qualifications of the bidders are reviewed and a recommendation is made to the owner.

How does new development change road needs?

  Buy Photo

When a new industrial development sprouted on Commerce Park Drive in southwest Cedar Rapids, Hoffman’s team worked on building a new road to support the new buildings.

“And that drove additional demand on the access at Sixth Street where it comes off,” Johnson said. “And then I worked with the city on doing a new project to improve the access modifications.”

The original plan was to widen Sixth Street SW to provide a northbound left turn lane and a southbound right turn lane. At that time, a traffic study of the southwest side of Cedar Rapids — conducted by another engineering firm — concluded and it was decided that a roundabout was needed at that location.

“Due to the fact that additional lanes on this roundabout would not be needed for at least 10-20 years, the City decided to build this out as a single-lane roundabout that could be widened in the future,” Johnson said.

The roundabout was designed so that it could be widened without major changes to the existing single-lane roundabout. Plus, Johnson said preliminary plans for the future multilane roundabout were prepared so an adequate right of way “was secured from the surrounding properties that were currently developing.”

How are roads built to last?

  Buy Photo

Roads can be designed with life spans, although a 40-year design life is common. While repairs may be needed before that 40-year mark, the design life indicates when a street will need to be dug up and replaced.

“There’s certainly streets that are well over 40 years that haven’t been [repaired]. Because of funding, they typically do exceed the years.” Johnson said. “But that’s what we’re designing for initially.”

The road’s thickness varies by intended street use.

“So for instance, like an industrial street where you have heavy loaded semis," Johnson said. ”It’s going to have a much thicker pavement profile … and so the pavement thickness would be less with the residential subdivision, obviously.“

Have a question for Curious Iowa?

Tell us what to investigate next. Curious Iowa is a Gazette series that answers readers’ questions about our state, its people and the culture.

Comments: bailey.cichon@thegazette.com