You may have noticed, but we like to show you photos of our ongoing construction projects. 

Partially it's because we get some great shots as asphalt goes down, girders go up, rocks go "boom" or signs go in. But it's also because it's not always easy to see progress being made as you are driving through a construction site to get home, to work or to wherever you might be heading.

That might be the case with the current phase of our project to replace the Interstate 17 bridge at Central Avenue. Some parts have been noticeable; anyone driving on the I-17 in central Phoenix will have noticed that since June the road has been narrowed to two lanes in each direction and traffic has been using only the northbound side of the old bridge. You may also have seen when demolition work on the southbound bridge was ongoing earlier this summer.

But the photos to the right show something that's a little more difficult to notice: Crews hard at work building the piers that will eventually support the new southbound bridge. While this new structure won't be finished until early next year, you can see that progress is definitely happening.

Once the new southbound bridge is finished, there will be more noticeable changes. Traffic will be switched to the recently finished structure, and then it's the northbound side's turn to be knocked down and built back up. The project is schedueld to be completed in fall 2021, so drivers should continue to expect delays in the area while I-17 is narrowed to two lanes in each direction. They should also consider using Interstate 10 if they are going beyond the downtown area. 

As part of the $13.5 million rebuild, we are improving upon the original bridge that has serviced drivers since 1962. The new bridge will raise the clearance on Central Avenue from 14 to 16 feet, which will also allow for the future extension of the Valley Metro light rail south of the downtown area. Plus, the structure will be wide enough to accommodate future work to add auxiliary, or merge, lanes along the right shoulder of I-17 in both directions between the on- and off-ramps at Seventh Street and Seventh Avenue.

We think you'll also notice – and appreciate – that.

It’s happening!

The new diverging diamond interchange (DDI) at Interstate 17 and Happy Valley Road is scheduled to open to motorists sometime in mid-October.

The innovative Arizona Department of Transportation interchange paves the way for a slew of benefits: Better traffic flow, fewer “conflict points” between traffic traveling in opposite directions and thus, improved safety.

ADOT has worked closely with the city of Phoenix and Maricopa Association of Governments (the Valley’s freeway planning agency) in designing and now building the state’s first major diverging diamond interchange. The DDI design has been growing in use across the country for its innovative features. 

As mentioned above, diverging diamonds provide safety benefits by reducing the number of conflict points at intersections within the interchange. Those are locations with opposing directions of traffic. A potential conflict exists every time a vehicle crosses or turns across the path of another direction of traffic.

For example, at the Happy Valley Road DDI, intersections and traffic signals will allow drivers to cross to the left side of the bridge over I-17 and thus have a direct turn onto the freeway on-ramp. They are able to make that left turn without facing traffic in the opposite direction.

Reducing such conflict points as well as overall traffic-signal movements also allows more traffic to move through the interchange in a shorter amount of time. That helps to limit wait times for drivers, especially during times of busier traffic.

While you may be unfamiliar with such an interchange, studies and observations in other states have shown motorists quickly get the hang of traveling in a DDI. The use of noticeable pavement markings also helps direct traffic. You can see how it all works in the video to the right..  

ADOT State Engineer Dallas Hammitt discussed the benefits of a DDI in a blog earlier this year about two smaller diverging diamonds (called “half DDIs”) now in use along the Loop 202 South Mountain Freeway.

“This type of interchange works by temporarily transitioning traffic to the left side of the road, allowing through-traffic and left-turning traffic to proceed through the interchange simultaneously, eliminating the need for a signalized left turn.”

Crash rates improved dramatically after a diverging diamond interchange was constructed in Springfield, Missouri, according to the Federal Highway Administration. The study compared crashes from the first year after construction to the five-year average before, and found the following:

• Left-turn crashes were totally eliminated.
• Right-angle crashes were reduced 72 percent.
• Rear-end crashes were reduced 29 percent.
• Total crashes were reduced 46 percent.

“Where they have been built,” the FHWA report said, “travelers save time, agencies saved money, and communities will benefit from safer facilities for many years.”

There's an idea out there called creative destruction. It basically says that tearing down the old is sometimes necessary to make way for the new. This has been applied to everything from economics to the arts, but we found it very fitting recently for our project on Interstate 17 over Central Avenue.

As you can see in these photos, crews spent a busy weekend recently tearing down the old southbound bridge. Now that the old bridge (built in 1962, by the way) is gone, we can go ahead and start building its replacement. Traffic was switched to using only the northbound bridge back in June. When the southbound bridge is finished early next year, traffic will be switched again to use that and the whole process of creative destruction will begin on the northbound side.

Drivers should continue to expect delays in the area while I-17 is narrowed to two lanes in each direction. They should also consider using Interstate 10 if they are going beyond the downtown area. 

But we aren't tearing down just to erect something similar in its place. The new bridge will raise the clearance on Central Avenue from 14 to 16 feet, which will also allow for the future extension of the Valley Metro light rail south of the downtown area. Plus, the structure will be wide enough to accommodate future work to add auxiliary, or merge, lanes along the right shoulder of I-17 in both directions between the on- and off-ramps at Seventh Street and Seventh Avenue.

Once the creative destruction is all over, we think you’ll like what we will have created.

The whole $13.5 million project is scheduled to wrap up in fall 2021. You can learn more on our website. 

The important ongoing project to reconstruct the Interstate 17 bridge over Central Avenue south of downtown Phoenix remains in an early stage. But before the work got started, our staff at ADOT knew the bridge work zone would present challenges for drivers who use the stretch of I-17 between the I-10 “Stack” and “Split” interchanges.

A decision was made to incorporate a “Smart Work Zone” safety innovation into the I-17 project at Central Avenue. As you can see in this ADOT video, the project team has followed through with the placement of portable message signs on trailers at nearby freeway locations to provide drivers with travel times for both I-10 and I-17 in the downtown area.

For example, one of our message signs along westbound I-10 near Phoenix Sky Harbor International Airport provides both I-10 and I-17 travel times. That allows drivers to compare the estimated travel time for using northbound I-17, which includes the work zone, or what to expect by staying on I-10 in the downtown area.

On average, the optional I-10 route that includes traveling through the Deck Park Tunnel is saving drivers five or more minutes of commute time, not to mention avoiding the frustration associated with slow moving traffic in a work zone. Even with lighter traffic conditions on freeways during the current health situation, there are times when slow downs and backups occur on I-17 in the area approaching the bridge work at Central Avenue.

The portable sign system uses traffic data to calculate the estimated travel times to predetermined destinations. This system is much like the one used to provide drivers with valuable travel times on ADOT’s permanent electronic message boards along Valley freeways.

As part of this pilot project, portable message boards also have been placed in areas along I-10 approaching interchanges connecting to the new Loop 202 South Mountain Freeway. Those signs also provide drivers with estimated travel times for using either Loop 202 or I-10 through the downtown Phoenix region.

ADOT has recently established several Smart Work Zone initiatives to help offset challenges associated with keeping traffic moving while construction is taking place. Those innovations include an I-15 queue warning system in the Virgin River Gorge, providing drivers with information to prepare for stop-and-go conditions ahead. Another example is the I-40 dynamic merge system east of Flagstaff that adjusts methods for merging depending on conditions near a bridge project at Meteor Crater.

Work to build a new, larger Interstate 17 bridge over Central Avenue south of downtown Phoenix is now underway as ADOT and partner agencies look ahead to improvements beyond the freeway itself. But the progress also means drivers should consider using alternate routes, including Interstate 10, while the bridge reconstruction requires I-17 lane closures.

The current I-17 bridge, dating back to 1962, provides clearance of just under 14 feet for vehicles passing underneath it along Central Avenue. ADOT’s $13.5 million project will provide a new structure with clearance of approximately 16 feet, which certainly helps with the movement of today’s larger commercial vehicles as well as the variety of construction equipment that is often hauled on trailers.

Meanwhile, the timing of the I-17 bridge reconstruction has been coordinated with the city of Phoenix and Valley Metro, since the modernized bridge will allow the future Central Avenue light rail line to extend south of the downtown area.

If you’re a driver who uses the stretch of I-17 between the I-10 “Split” interchange near Phoenix Sky Harbor International Airport and the I-10 “Stack” south of McDowell Road, you should plan ahead for lane restrictions now that a work zone is established in the area between Seventh Street and Seventh Avenue.

I-17 is now narrowed to two lanes in both directions approaching Central Avenue. By early June, additional work will be done to temporarily switch I-17 traffic to one side of the freeway so that the first half of the new bridge can be built. The freeway will operate with two lanes in each direction outside of times when closures or other restrictions are needed for work, mostly during overnight hours or on some weekends. That’s why it might be a good idea to use I-10 as a way to travel beyond the I-17 bridge construction zone.

The entire project is scheduled for completion in fall 2021. Additional information is available at azdot.gov/I17CentralBridge.

When finished, the new I-17 bridge will have been widened enough to accommodate a future project to add auxiliary, or merge, lanes along the right shoulder of I-17 in both directions between the on- and off-ramps at Seventh Street and Seventh Avenue.

It’s another step forward in what regional planners see as major improvements to help manage the traffic needs along one of the original backbone freeways in the Valley of the Sun.

It's a question that occasionally pops up on our social media feeds: Why is it called Interstate 17?

And it's not the "17" part they are asking about.

Rather, it's the fact that all 147 miles of highway runs between Phoenix and Flagstaff ... and that's it. How can it be called an "interstate" when it never reaches outside of Arizona? The same question can be asked about Interstate 19, which runs 102 kilometers (63 miles) between Tucson and the international border.

If we went solely off Webster's definition of "interstate," it admittedly doesn't make much sense. But when we talk about interstate in terms of highways, we have to turn to a different criteria. 

According to the Federal Highway Administration, the Federal-Aid Highway Act of 1956, which created the system, called for uniformity in construction standards. These standards were developed by the American Association of State Highway Officials (now the American Association of State Highway and Transportation Officials or AASHTO) and are the benchmark for any highway that wants to be an interstate. The metrics include having controlled access, design speeds of 50 to 70 MPH depending on terrain, a minimum of two travel lanes in each direction, 12-foot lane widths, a 10-foot right shoulder, and a 4-foot left shoulder.

And the criteria for adding another highway to the system is also straightforward: it must meet the interstate standards, be a logical addition or connection, and be coordinated among all jurisidictions it will pass through.

The Federal Highway Administration also has a fantastic page dedicated to debunking myths about the interstate system. There the agency specifically address highways that don't ever leave their state of origin.

"The key," according to the Federal Highway Administration is "each highway must meet Interstate standards, be a logical connection to the interstate system, connect to an existing route or be a congressionally designated future interstate corridor that eventually will connect on at least one end." 

This definition is why you'll see interstates that are beltways around large metropolitan areas or in places such as Hawaii, Alaska and Puerto Rico that cannot connect to other states. It's also why I-17 and I-19 both can be called interstates.

Though they don't go anywhere nearly as far as I-40 or I-15, both I-17 and I-19 have fascinating histories that can give additional insights into these intrastate interstates.

Anyone who’s driven on Interstate 17 near Sunset Point this time of year has witnessed the mystery of a scrub tree in the median suddenly decorated with holiday finery. 

Many refer to it as the Mystery Tree.

For more than 30 years, someone has secretly decorated it in the middle of the night. Like magic, the tree suddenly gleams with ornaments to the delight of those who pass.

How does this happen? Who decorates the tree? Why doesn’t anyone see them?

Perhaps no Arizonan has captured this mystery better than Dolan Ellis, Arizona’s official balladeer for more than 50 years. Ellis might look like a rough and tumble cowboy with his hat, boots and guitar, but this baritone sings from the bottom of his soul.

Ellis named the tree Scrubby and commemorates it in a song of the same name, which he performs in this video produced ADOT's video team.

The first verse:

Out in Arizona there’s a story to be told.
Of Scrubby, the little cedar tree that grows beside the road.
I-17 to Flagstaff, from the desert down below,
And a random act of kindness by some secret, caring soul.

It’s the idea that people care enough to bring joy to others that strikes a chord with Ellis, whose own generous spirit spreads across his face as he sings the song, sharing the joy still further.

It brings a smile to every face that passes by that sight.
Scrubby becomes a rock star, and for him this song I write.

The song is one of hundreds Ellis has written since crossing the Arizona state line with his pregnant wife in 1959. During his storied career he has performed before millions of people and won a Grammy Award while a member of the New Christy Minstrels.

He has sung songs for hundreds of thousands of Arizona schoolchildren and been inducted into the AZ Music and Entertainment Hall of Fame, among many other career highlights.

He has logged countless miles across Arizona in four-wheel drive vehicles and explored every nook and cranny of culture and climate, guitar always at the ready.

Many of his songs are about Arizona highways and the places and sights that have led him into direct contact with the state, its people and its culture. 

Sights like Scrubby.

Scrubby is a cedar tree and no one knew his name.
Till someone decorated him, and gave him pride and fame.

You can learn more about Ellis, his performance schedule, history and songs at DolanEllis.com. You can also learn about the Arizona Folklore Preserve in Ramsey Canyon in the Huachuca Mountains, which Ellis founded to preserve songs celebrating Arizona’s western heritage and culture, at ArizonaFolklore.com.   

Sept. 26 was a big day, both for us and for everyone who drives on Interstate 17 north of the Valley.

As we said in a news release, Governor Doug Ducey, accompanied by ADOT Director John Halikowski, the heads of the state Department of Public Safety and state Office of Tourism, and business leaders, elected officials and transportation stakeholders, announced more than $300 million in improvements coming to the highway between Anthem and the Sunset Point Rest Area. These include adding a third lane in both directions on the 15 miles between Anthem and Black Canyon City and 8 miles of flex lanes on the grade between Black Canyon City and Sunset Point. 

This announcement stemming from state, local and federal partnership, including $130 million proposed in Governor Ducey’s executive budget, came during an event in Anthem, just a stone's throw from where the freeway can see more 50,000 drivers on especially busy days such as the beginning and end of holiday weekends.

As you can see in the slideshow to the right, lingering storm clouds couldn't dampen our enthusiasm for this project, which is scheduled to start in 2021 and be completed in 2023.