By David Rookhuyzen / ADOT Communications

If you’ve driven Interstate 10 in Casa Grande recently, then you probably noticed work going on to expand the freeway to three lanes in each direction near Interstate 8. That includes expanding bridges carrying I-10 over Jimmie Kerr Boulevard and the Union Pacific Railroad tracks.

Next year cars will use the larger bridge on a wider I-10 without giving much thought to the engineering behind it. But for now they can see the new vertical supports known as piers capped by what are known as – wait for it – pier caps. Pier caps creating the horizontal section in the picture above will eventually support bridge girders.

Erin Kline, an engineer on the project, explained the role these vertical concrete beams will eventually play.

“Pier caps transfer the loads from the superstructure to the piers. They hold the bridge girders on bearing pads and disperse the loads from the bearings to the piers. Bridges with piers will all have pier caps to transfer the load from the superstructure. I would say majority of the bridges in Arizona are like this,” Kline said.

We’ll have more to say about the anatomy of this project moving forward. For now you can read more about the coming improvements at the project's website.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained...leave a comment here on the blog or over on our Facebook page!

By Tom Herrmann / ADOT Communications

From the time Interstate 10 arrived in Tucson in 1965, we've worked to make sure the freeway kept pace with Pima County’s growth.

Growth in southeast Pima County is translating into more vehicles on I-10. Since 2012, average daily traffic on I-10 at Kolb Road has increased by nearly 20 percent to almost 50,000 vehicles each day.

That’s the reason behind the work we’ll be doing for the next seven months where I-10 meets Rita, Wilmot and Kolb roads. We’re replacing stop signs at the end of each exit ramp with traffic signals that will move traffic more efficiently on and off the freeway and reduce delays when you’re trying to get home at the end of a workday. We’re also adding lanes on the eastbound exit and westbound on ramps at Rita Road.

That’s not all. Two years from now we will rebuild the traffic interchange at Houghton Road with a diverging diamond design. It’s safer and moves traffic more efficiently than traditional interchanges.

Right now we’re adding a new surface to the bridge at Wilmot Road to make it last for years to come, just as we did at Craycroft Road last year. We’re using a temporary bridge to maintain two lanes of traffic in each direction and avoid delays.

As this area of Pima County grows, we're right there with you.

By Tom Herrmann / ADOT Communications

If you stand at the east end of the Ina Road bridge over the Santa Cruz River in Marana, it looks like the bridge goes on forever.

That’s not quite true, but the bridge that should begin handling traffic by the end of the year is longer than most in Arizona. It’s 640 feet long – more than the length of two football fields – and longer than the longest home run in major league history (Babe Ruth hit one 575 feet back in 1921).

ADOT crews put girders in place for the new westbound bridge in mid-May. The structure is almost identical to one we built in 2017 that eventually will carry two lanes of eastbound traffic toward Interstate 10 about a half-mile away.

Here are more numbers when it comes to the Santa Cruz River bridges:

• With the help of a crane and some very strong ropes, we placed 54 girders to support the bridge.
• There are nine piers holding up those 54 girders.
• Six girders, running the same direction as the bridge, rest on each pier.
• Each girder weighs 45,000 pounds, or about 22.5 tons.
• Combined, that’s 2.43 million pounds – 1,215 tons – of girders ready to support the roadway that will cross the bridge.

The next big step: Pouring the deck and superstructure of the bridge later this year. That will involve pouring 946 cubic yards of cement. At 2 tons per cubic yard, we’ll be pouring, smoothing, curing and striping nearly 1,900 tons of concrete for this bridge alone.

Looking at the bridge from below reveals that the girders curve upward just a bit. That’s to allow each to drop down just a little when the deck is poured into place.

ADOT is overseeing a $128 million project creating a modern traffic interchange that includes a bridge carrying Ina Road traffic over Interstate 10. We're also widening the interstate and making Ina Road two lanes in each direction west of I-10. The project remains on track for completion in early 2019.

The town of Marana is contributing $7.9 million toward the cost of the Santa Cruz River bridges and the rest of the funding is from the Federal Highway Administration, the Pima Association of Governments and the Regional Transportation Authority.

By Laurie Merrill / ADOT Communications

This vintage photo shows construction of the final piece of Interstate 10 through a series of bridges near downtown Phoenix.

Snapped in 1989, the picture captures crews paving Central Avenue atop the Papago Freeway Tunnel, better known as the Deck Park Tunnel.

Today, the mighty half mile of I-10 carries hundreds of thousands of vehicles daily under Margaret T. Hance Park next to the Burton Barr Central Library.

Finished in 1990, it was celebrated as the last piece of freeway needed to complete the I-10 in its 2,500-mile entirety between Santa Monica, California, and Jacksonville, Florida.

The photographer who captured the paving also snapped a slice of Phoenix life. The picture, looking south near Portland Street, was taken in the same year that the elder George Bush was elected president, the Berlin Wall fell and NASA launched the Galileo spacecraft.

Residents arriving after this ADOT project may not recognize Central Avenue. There have been significant additions in the ensuing years, not the least of which is the Valley Metro light-rail line.

Many of today’s buildings, however, were present in 1989. Then as now, the Westward Ho building can be seen on the west side of Central – on the southern end of the picture – towering over its shorter neighbors.

The first building on the right, once the site of the Lexington Hotel, was built in the 1970s and now houses the artsy FOUND:RE Phoenix hotel at the corner of Central and Portland.

The tunnel has become such an integral part of Phoenix that it may surprise some to learn that it’s not really a tunnel. The freeway actually travels under 19 side-by-side bridges.

By Tom Herrmann / ADOT Communications

The last time you went to the gym, how much weight did you lift? More than 100 pounds? 200?

More than 75 tons, anyone?

Those building a new bridge connecting Interstate 10 and State Route 87 in Eloy didn’t really lift 20 tons, of course. But 30 feet above the ground today, as two cranes lifted huge girders into place, these professionals, securely perched atop bridge piers, made sure these 145-foot girders landed in just the right spot.

And they repeated the process over and over, as shown in the slideshow above.

Precision may be difficult with a heavy girder, but it’s essential. There needs to be the right number of girders across each pier to support the bridge deck and traffic over decades. And each girder must allow room for the one that will connect to the next pier.

Today marks six months since crews began clearing ground for new lanes of I-10 and the new interchange with SR 87. Placing girders on the bridge is another visible sign that work is continuing on schedule.

The project is creating six new lanes of I-10 that will connect with the existing freeway just west and a few miles east of SR 87. Traffic will be moved to the new pavement as soon as this fall, with the entire project scheduled for completion by fall 2019. After this project and another in Casa Grande are complete, I-10 will be three lanes in each direction all the way between Casa Grande and the east side of Tucson.