The Munds Park traffic interchange on I-17 has come a long way since we first checked in on construction...

That was back in May 2011 when work on the project had just gotten started. Since then, crews have reconstructed bridges and made other improvements to the site located about 20 miles south of Flagstaff.

We’ve been interested to watch the project progress and we think the video above gives a good look at how it has taken shape. But, as we viewed the video, we also started to notice how well it showcases many of the transportation concepts we’ve covered before here on the blog.

That’s when we had the idea to take note of all the previous blog topics that were being mentioned or shown. We thought it’d be fun to see if you can spot all these subjects as you’re watching the video:

• Work zones
• Winter shutdown
• Bridge demo
• Box girders
• Bridges
• Safety
• Bicycle/pedestrian issues
• Friction course
• Rubberized asphalt
• Aggregate
• Seeding
• Wattles

So, did we get them all? Did you notice any others? Let us know in the comments!

As you can see in the video above, girders are the concrete and steel beams that enable the bridge to support the roadway and the vehicles on top of it.

They’re vital to the design of a bridge, but not all girders are the same…

Just like each bridge in Arizona is individually designed to hold up in the conditions unique to its surroundings, girders differ in size, shape and type, depending on the situation in which they’re being used.

This is a topic that can get complex real fast, so we’re going to keep it simple today by just focusing on two types of concrete box girders: prestressed concrete box girders (these are featured in the above video) and post tension concrete box girders.

But first, we’re going to need to look inside the girder itself…

The girders we’re referring to are made up of very strong steel strands or rods that are surrounded by concrete. The difference between the two types of girders hinges on when the tensioning (or stretching) of the steel takes place – it’s either before or after the concrete is poured.

Tensioning, by the way, is done to give the concrete some additional strength. This explanation from the ADOT Construction Manual might help better explain the need for tensioning/stretching:

Concrete is strong in compression and weak in tension. Reinforcing steel is generally used to carry the tensile loads placed on a concrete structure … Reinforcing steel is used to help concrete carry compressive loads and shear stresses that develop when loads move through a structure.

If a girder is prestressed or pretensioned, the steel strands are stretched to a predetermined stress and then concrete is poured around the strands.

“Once the concrete has hardened and gained sufficient strength, the ends of the strands are cut. The strands inside the concrete try to relax and shorten. However, there is now concrete bonded to the strands. As the strand shorten, they push the concrete together and induces a compressive stress into the concrete,” according to the ADOT Construction Manual.

More from the manual regarding post-tensioning…

Post-tensioning involves running steel ducts through the concrete (girders). Special anchors are placed at each end of the (girder). Then concrete is poured around the ducts and the anchors. Steel strands are run through the ducts. Once the concrete is strong enough, the strands are pulled at one end while anchored at the other.

Pulling (or jacking) of the strands causes the ends of the concrete (girder) to push toward each other. This induces compressive stresses along the entire length of the concrete member. After jacking, grout is injected into the ducts then concrete is poured around the ends of the anchors. Once the grout gains strength, the strand is now bonded to the concrete member in a way similar to pretensioning.

When to use prestressed vs. post-tensioned girders

State Bridge Engineer Jean Nehme says that using prestressed box girders is sometimes more convenient because they’re constructed off the project site.

“Because you build them off-site, you cut down on the time of construction,” said Nehme, adding that using prestressed girders can cut down on the need for traffic closures.

But, whether the girder is prestressed or post-tensioned, Nehme says by tensioning the reinforcing in the concrete, engineers can design stronger bridges that span longer distances.

“It provides better durability in the long term,” he said.

By Ryan Harding
ADOT Office of Public Information

A different sight greeted the staff at the Grand Canyon National Park Airport on Dec. 3 when instead of tourist helicopters, two U.S. Marine Corps CH-46E Sea Knight helicopters landed to engage in their annual mission to deliver toys and food to members of the Havasupai Tribe who live at the bottom of the canyon.

This event, known as Operation Supai, has been conducted every year by Marine Medium Helicopter Squadron 764 (HMM-764) based out of Edwards Air Force Base in California.

The Grand Canyon airport, owned and operated by the Arizona Department of Transportation, provides support to this Marine squadron every year by providing jet fuel, a temporary base of operations and local ground transportation before and during the mission. In past years when snowy conditions threatened the success of the operation, ADOT staff would plow the landing pads and runway so the squadron could still deliver goods to the tribe.

“The support ADOT provides is invaluable,” said Major Charles Nunally, executive officer and helicopter pilot for the squadron. “Without the support of the airport, we wouldn’t be able to do this mission.”

HMM-764 partners with the local Marine Toys for Tots program based in Flagstaff and St. Mary’s Food Bank every year to bring 150 bags of toys to over 100 children and 100 boxes of food and turkeys to the small, remote tribe. Their CH-46 helicopters allow them to deliver the goods down into the Grand Canyon where the Havasupai live. The Grand Canyon airport serves as a staging area to load goods and personnel and refuel the helicopters.

“This is the biggest day of the year for the tribe,” said Rick Wiselus, a Toys for Tots volunteer and board member on the Marine Corps League Charities. “The smiles on the kids’ faces are heartwarming. The airport is wonderful to us every year. They pull together to help us.”

Operation Supai began in 1995 when the Northern Arizona Marine Corps League requested a squadron to deliver goods to the Havasupai. HMM-764 was selected for the mission, and they have delivered goods every year for 17 years to the tribe which consists of around 300 people.

The Havasupai Reservation is remotely located near the southwest corner of the Grand Canyon National Park outside of the main park area. They are largely dependent on tourism as their primary source of revenue. This annual Marine operation is something the Havasupai have come to depend on every year.

“We are honored to help the Marines with this operation every year,” said Mike Halpin, Grand Canyon airport manager, who also served in the Marines as captain of an air wing. “This is an important event for the Havasupai and we are glad to provide support in any way we can.”

As you can see in the video above, applying for and receiving a Class C permit from ADOT isn’t just a formality – it’s a critical step that helps ensure safety on the state’s roads.

These Class C permits (which are required for oversized/overweight loads that are either in excess of 250,000 pounds, measure more than 120 feet in length, 16 feet in height or 14 feet in width) are vital because when a transport hauler applies for one, it allows ADOT to analyze all the specs and make sure a load can safely make it along its route.

Making ADOT aware that such a heavy load is about to enter onto its highways, gives Class C Supervisor Chris Pippin and her team the chance to communicate with various ADOT district engineers to make sure current road conditions and construction projects are accounted for in the final route.

“I just want the people of Arizona to understand that what we do here at the state in issuing these Class C permits that we do everything we can to keep the motoring public very, very safe,” Pippin says in the video above.

State Bridge Engineer Jean Nehme underscores that point by commenting on what’s at stake when it comes to bridge safety.

“You need to make sure the bridge capacity can handle the additional load,” he says. “If you exceed those loads repeatedly, the pavement will have to be replaced sooner, the bridges may deteriorate, or you may have a failure. So, if you’re exceeding what’s permitted within the legal weight limit, then that’s why permitting is necessary.”

To learn more about oversized loads and Class C permits, check out our previous blog posts August 9, 2011 and August 22, 2011.

Public involvement truly helps shape ADOT projects … just ask residents living near the San Pedro River Bridge.

Their local bridge sits on SR 90 and is slated for replacement – construction has already begun, in fact.

But, way before work got started earlier this week those residents took part in several ADOT public meetings where they were given a couple of different construction schedule alternatives.

One option called for a full closure of SR 90 at the San Pedro River…

That choice would have allowed the bridge replacement to wrap up in a six-month time frame, but it would have meant very lengthy detours for residents. The option was eliminated after comments from residents indicated a preference for a longer project schedule that would be able to keep SR 90 open through the duration.

18-month construction schedule – no extended full closure
“We’ll have a six-month construction period, six months of shut down for the summer migratory bird season in the San Pedro riparian wilderness area, which is where the bridge project is, and then six more months to finish the bridge,” says ADOT Senior Community Relations Officer C.T. Revere.

What else do drivers need to know?
This bridge, constructed in 1955, will be replaced by a new structure featuring wider traffic lanes and shoulders that meet current standards and provide adequate space for vehicles – including emergency responders, bicycles and pedestrians.

Construction on the $7 million bridge replacement project started Oct. 1 and once work is complete (by spring 2014), drivers can expect:

• A new 44-foot wide bridge that replaces the existing 26-foot wide bridge.
•  Two 12-foot traffic lanes and 10-foot shoulders in both directions.
• Improved guardrails, and roadway and bridge approaches.
• A new bridge that’s six feet higher than the existing structure (this is to comply with 100-year floodplain requirements.

Drivers also should take note of this project’s impact on traffic…

• A temporary traffic signal will guide alternating traffic through a single shared lane during construction. Wait times are expected to be 5 to 8 minutes, with delays of up to 15 minutes possible. Motorists are advised to plan ahead and allow extra travel time.
• Some overnight closures of SR 90 will be required for the safety of the public. Those scheduled closures will be announced in advance.
• ADOT intends to have one lane open in each direction with no traffic signal during the season that construction work is shut down.

To say that ADOT crews were busy Tuesday would be a bit of an understatement.

Heavy overnight and morning rains across the state started the day off with extremely slow commutes throughout the metro areas … but nothing like the messes that would happen later in the day …

First off, an oil tanker overturned on State Route 87 about 30 miles south of Payson, pouring approximately 2,000 gallons of emulsified asphalt across travel lanes in both directions. As you can see in the video above and the slide show below, the ensuing cleanup efforts were, to quote our own PIO, “a big gooey mess.”

North- and southbound lanes were closed at about 11:30 a.m. as 50+ crew members from three agencies — ADOT, DPS and Arizona Department of Environmental Quality — and the private cleanup company hired by the responsible party (the company that owns the tanker and employs the driver) worked to clear the road and prevent the hazardous materials from spreading into nearby Slate Creek.

Southbound lanes were reopened within a few hours, but cleanup of the northbound lanes between the Saguaro Lake exit and SR 188 continued through the night. All lanes were reopened at about 3 a.m.

On a few positive notes, though … the driver sustained only minor injuries, there were no other vehicles involved in the crash and crews were able to stop the liquid before it reached the creek.

(And, as a side note … the “responsible party” is also responsible for paying for the cleanup efforts. But more about that in a future post dedicated to all-things ADOT HAZMAT related.)

View SR 87 oil tanker rollover photos on Flickr

Elsewhere in the state …

Heavy rains further north caused water to flow over a bluff above SR 264 just east of Tuba City in Navajo County washing out the roadway.

ADOT crews reopened the roadway last night and are still working to complete additional  permanent repairs. As you can see in the slideshow below, the damage was pretty extensive.

 … and people think it never rains in Arizona …

Construction had only recently started back when we first checked in on the SR 64 highway improvement project…

That was about a year ago. Since then, well, just take a look at the video above and see for yourself how much this project has transformed the area’s landscape!

Work is now complete and the town of Tusayan (pop. 560) has a wider roadway, two new roundabouts, new bus pull-outs, enhanced landscaping, and several new crosswalks.

The upgrades were necessary because this small town happens to sit along the route leading to the popular south entrance of the Grand Canyon National Park. That means that Tusayan sees a lot of traffic (pedestrian and vehicle), so the lack of crosswalks and traffic signals had caused some concern.

The improvements are a welcome sight, according to Tusayan Mayor Greg Bryan. He says now people have a place to properly cross the street.

“The safety factor coming through Tusayan has been vastly improved,” Bryan said.

Here we are, past the halfway point on the I-17/Cordes Junction interchange project and it’s clear that work is really moving along!

At least, it’s clear if you drive the area frequently, or if you watched this video back in February. Crews have been busy since then, as you can see above.

Project details

When construction is complete (by next summer), drivers will have a new, modern interchange designed to handle the area’s growing needs.

Some of the project’s new features include:

• New bridges on SR 69
• The removal of the outdated on- and off-ramps
• A new I-17 interchange constructed north of the existing interchange
• A new bridge built over I-17 to connect with SR 69 (note: the existing bridge is being rehabbed) 
• The construction of a new Arcosanti Road along with the realignment of Copper Star Road and Stagecoach Trail 
• Reconstruction of the I-17 bridges over Big Bug Creek 

“It will be nice. When this project is complete there will be more access in to and out of the communities and if you want to head west toward Prescott and the cities in that direction you’ll be able to do that with a little more ease,” says Resident Engineer Sam Patton in the video above.

Traffic Alerts

Because I-17 is such a major corridor, ADOT has taken a lot into consideration when determining the construction phasing.

There are a few restrictions in place this week (weather permitting) as crews work on new bridges …

Tonight (Aug. 28), drivers on southbound I-17 will be shifted onto the off and on ramps at Arcosanti bridge from 7 p.m. to 6 a.m. to allow crews to work on the new bridge over I-17.

On Thursday (Aug. 30), drivers can expect:

• Intermittent full closures of I-17 are expected for up to 15 minutes at a time between 11 p.m. and 3 a.m. for bridge work over I-17.
• The on-ramp from State Route 69 to northbound I-17 will be closed from 7 p.m. to 6 a.m. Traffic will be detoured three miles south on I-17 to Bloody Basin Road (Exit 259) and then directed to use I-17 northbound.
• Traffic will be narrowed to one lane in each direction and will be diverted to the southbound lanes through the work zone from 7 p.m. to 6 a.m. as crews work on the flyover bridge above I-17.

The work zone will be clearly marked by temporary barricades and signage. ADOT advises drivers to allow additional time to reach their destinations and to proceed through the work zone with caution, comply with the reduced speed limit and be alert for construction equipment and personnel.

By Kimberly Noetzel
ADOT Public Education Manager

The Phoenix-area's newest pedestrian bridge is in place over Interstate 17 just north of Happy Valley Road.

ADOT installed the 160-ton, 600-foot long bridge over two nights in June next to the Central Arizona Project (CAP) canal.

Working in partnership with the CAP, city of Phoenix and Federal Highway Administration, ADOT designed and built this bridge to provide long-term connectivity for the CAP's multi-use recreational trail. Because the city of Phoenix will maintain the bridge, ADOT designed it to require only minimal maintenance after installation.

When you drive under or walk over the bridge, you might wonder why a new structure looks so … weathered. The answer? Weathering steel. Crews used weathering steel which, by design, gives outdoor structures a rustic appearance. Better yet, it never needs to be painted, which significantly reduces maintenance costs.

Weathering steel has what’s known as a "sacrificial surface." This means it rusts only on the outside. The base metal (structural component) does not rust. If you hail from the eastern United States, you might know that some big, old steel bridges need to be replaced over time because they rust all the way through and weaken...

But, with weathering steel, the load-bearing capacity and long-term durability of a bridge or other structure are not compromised.

In the Metro-Phoenix climate, the weathering process usually takes about six months and a couple of good rains. But for this project, we’ll let you in on a little secret: to jump start the weathering process crews sandblasted the steel and hosed it down prior to installation, making our new bridge look older than it really is to complement the natural environment.

The bridge, which is accessible from the CAP trail, is now open.

According to one dictionary’s definition, engineering is “the art or science of making practical application of the knowledge of pure sciences, as physics or chemistry, as in the construction of engines, bridges, buildings, mines, ships and chemical plants.”

Sure, it’s an accurate description, but do you get any real sense of what an engineer does from reading that?

We didn’t think so.

To learn about engineering, it helps to hear firsthand from the men and women who work in the field.

Recently, a group of high school students from around the state got to do just that…

It was all part of ASU’s Summer Transportation Institute – a program designed to teach future engineers what it takes to make traffic flow in a safe and effective way.

The students traveled across Arizona during the three-week program and experienced everything from bridge-building basics to lessons in space travel and water transportation. They learned on-site at several locations, including the Hoover Dam and ADOT’s Deck Park Tunnel (see video above). At ADOT, the students also learned about engineering survey and photogrammetry, traffic engineering and equipment services.

It’s this direct approach to learning that instructor Dr. Jan Snyder says gets the kids engaged and fired up for a future career in engineering.

“You hear about STEM (Science, Technology, Engineering and Mathematics) … but until recently, the E in STEM was silent,” Dr. Snyder said. “It has become obvious to many of us that really, engineering provides an opportunity to bring the other three aspects of STEM together in a very interesting, enjoyable way.”

The students certainly seemed to agree…

Stefin Nelson, a junior at Kingman High School, said he’s always been interested in engineering and decided to apply for the institute after hearing about it from his biology teacher.

“I didn’t know there were so many different types of engineers,” Nelson said of what he’s learned from the experience.

Liliana Tapia, a senior at Kofa High School, is interested in civil and aeronautical engineering and, like Nelson and many of the other students, said she was surprised to see the numerous options available in engineering.

“It’s been a lot of fun,” Tapia said of the summer institute. “It’s cool to see how many jobs are created by this certain field.”

Aaron Witt, an Arcadia High School senior, already knows what he wants to do after college … he is looking toward a career in road building.

“I’ve really enjoyed it because we’ve gone through so many aspects of engineering. I want to get paid to play in the dirt and I wasn’t sure that was possible,” said Witt, adding that the summer transportation institute showed him it is possible.