By Kathy Cline / ADOT Communications

This bridge may look like a ruin in the middle of nowhere, but it's one of Arizona's earliest examples of vehicular bridge construction.

Canyon Diablo Bridge used to carry Route 66 over Canyon Diablo, about 30 miles east of Flagstaff (the ghost town of Two Guns is near its east end). According to the National Park Service, Arizona State engineer Lamar Cobb selected and surveyed the location; plans and specifications were purchased for $500 from the Topeka Bridge & Iron Co. Thomas Maddock of Williams, Arizona, built the bridge for $9,000.

Canyon Diablo Bridge opened to traffic in 1915. Designed to deal with occasionally violent floods through Diablo Canyon, its upstream wall was solid to protect the roadway, while the downstream wall had slots to allow water through.

At first, the bridge was part of the Santa Fe Highway (national name: Old Trails Road), which became part of U.S. Route 66 in 1926. This bridge fell out of use in the 1930s, when a new bridge was put up just to the north of this one. That bridge followed Interstate 40 at Two Guns.

The Canyon Diablo Bridge was added to the National Register of Historic Places in 1988.

Visiting this bridge is easy: Just take I-40 north to Exit 230 (Two Guns). You'll find the bridge along the historic Route 66, which goes through Two Guns.

By David Rookhuyzen / ADOT Communications

Travelers along State Route 89 south of Ash Fork will see the bridge over Meath Wash come down as crews begin the six-month process of a removing the old structure and replacing it with a cast-in-place, two-span bridge.

The original bridge dates back to 1932 and was widened in 1947.

The replacement bridge will look like the existing one with a few small differences, such as the spans being longer and the shoulders slightly wider. Crews will also reconstruct and re-stripe the approaches to the bridge to improve sight distance because of heavy traffic in the area from a cement plant.

A detour will direct traffic around the closed bridge. Motorists should expect delays in the area while the work progresses.

The bridge itself is expected to be closed for six months, though the overall project, which started at the end of January, is scheduled to last into October.

You can check out more information about the project, and subscribe for emailed updates, at its page on our website.

By Tom Herrmann / ADOT Communications

Driving along Interstate 10 as you passed Eloy in Pinal County, you may not have noticed the bridges that carried traffic over local roads. Six of them, three in each direction, allowed freeway traffic to flow without isolating the communities of Eloy and Picacho.

With new freeway lanes under construction as part of a 4-mile widening project, those six bridges built in the 1960s are no longer needed. The new freeway alignment and a new interchange at State Route 87 that reaches across I-10 will accommodate traffic on I-10 and in those communities.

And so, along with the old freeway lanes, those bridges are coming out. The westbound bridges at SR 87 and LaPalma and Phillips roads have already been taken down. The eastbound bridges will be removed as soon as eastbound traffic is switched to new lanes in January.

You can use the slider above to see the before and after (well, more like during) for one of these demolitions.

The concrete and asphalt from those bridges won't go to waste. We’re using everything freeway – 1 million square feet of asphalt, 30,000 feet of guardrail and 700,000 cubic yards of earth – to build the foundation of the new eastbound lanes. Some of the guardrail will be reused in other projects around Arizona.

By David Rookhuyzen / ADOT Communications

Today we're using a drone to provide a different perspective on work demolishing the old I-10 bridges over Jimmie Kerr Boulevard in Casa Grande, part of a project widening 4 miles of the interstate to three lanes in each direction.

In between the bridges that are on the way out, you can see new bridges over Jimmie Kerr Boulevard. On Jan. 9, we moved traffic to these bridges.

After the old bridges are removed, crews will add another lane and a full shoulder to each of the new structures.

The project is scheduled for completion in late summer at roughly the same time as another widening project just to the east between Eloy and Picacho.

By David Rookhuyzen / ADOT Communications

Today we are throwing back to this 1979 photo of construction work under Interstate 10 at the Salt River Bridge.

The photo didn't come with information on what is being done, but it's worth noting that seven floods swept through the Phoenix area between October 1977 and February 1980, including one in January 1979 that washed out many other Salt River crossings.

A flood in 1980, the year after this photo, closed every Salt River crossing except at Mill and Central avenues in Tempe and Phoenix, leading to a Maricopa County project deepening the Salt River channel and projects reinforcing all bridges.

The I-10 bridge pictured here was replaced in the mid-1980s with the bridge you will drive across today on the way to or from downtown Phoenix.

Recently, crews building the future Loop 202 South Mountain Freeway completed the decks of two half-mile bridges spanning the Salt River between Broadway Road and Southern Avenue.

In an area of the southwest Valley with few other all-weather crossings of the Salt River, the South Mountain Freeway will greatly improve mobility when water is flowing. And as this photo shows, that's always a possibility.

By Tom Herrmann / ADOT Communications

Every time you drive by an overpass, you see the cement-and-steel columns that support the roadway. There could be only a few on a small overpass, or more than a dozen in larger overpasses like the ones at two current projects on Interstate 10 in Pinal County. They usually hold the overpass 15-20 feet above what's below.

What you don’t see is just how low they go.

A typical bridge column drops down about 80 feet underground – about the height of an eight-story building.

Each pier includes a cylinder of rebar steel about 6-8 feet in diameter, woven into a lattice that creates hundreds of squares no more than 1 foot across. Each of those squares is tied together – by hand – to strengthen the concrete that is poured on top to create what's known as a caisson (this 2011 video shows the process).

Why so deep? Friction.

The bridge columns are in place not only to hold the overpass up but to keep it steady. It’s essential that each overpass be held firmly in place. The deep columns create friction with the surrounding ground, preventing the bridge from moving despite thousands of vehicles crossing a typical overpass every day, and weather bringing rain and crosswinds. Combine 10 or more columns and the friction is enough to hold a bridge steady for decades.

Overpasses like the ones being built today in places like Maricopa and Tucson are built to last 50 years or more. One way to make sure they serve that long is to give them a good foundation. By digging so deep, ADOT is doing just that.