Arizona Roads - Arizona Highways Map

History of Interstates and U.S. Highways in Arizona

Arizona's Interstates and U.S. Highway system is integral to the state's transportation and commerce, with a history that began in the 1920s with the creation of U.S. Routes 60, 70, and 80. These early highways connected the state to California, New Mexico, and other parts of the Southwest, providing vital trade routes. With the establishment of the Interstate Highway System in the 1950s, Arizona saw the construction of I-10, I-17, and I-40, which transformed the state's infrastructure and boosted its economy.

Today, Arizona's highways handle heavy traffic, particularly in urban areas like Phoenix and Tucson, where Interstates like I-10 can see traffic volumes of over 200,000 vehicles per day. Arizona's highways are also essential for moving goods, particularly along the I-10 corridor, which connects the state to major ports in California and Texas. The state's economy relies heavily on these highways for the transportation of goods, including agricultural products, electronics, and other manufactured goods.

Arizona is continually expanding its Interstate system to accommodate its growing population. Major projects include the widening of I-10 in Phoenix and Tucson, as well as the construction of the Loop 202 South Mountain Freeway in Phoenix, which will improve traffic flow in the metro area. Future projects include the proposed I-11, which would run from the Mexico border to Las Vegas, providing a critical new north-south route.

Why all the 1926 dates? The year 1926 was significant for the U.S. highway system because it marked the official establishment of the U.S. Numbered Highway System, also known as the U.S. Highway System. This system was created by the American Association of State Highway Officials (AASHO), now known as the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the federal government. Here’s why 1926 was pivotal:

1. Standardization of Routes: Prior to 1926, roads in the United States were a patchwork of local and state routes, often inconsistently marked and poorly maintained. The U.S. Highway System brought about a standardized network of numbered routes, designed to provide uniformity across state lines, making travel more predictable and navigable for drivers.
2. National Connectivity: The new system connected rural and urban areas across the country, linking small towns and cities with major economic hubs. This was essential for improving the transportation of goods and services, helping to bolster the national economy.
3. Designation of Major Routes: Iconic highways such as U.S. 1 (from Maine to Florida) and U.S. 66 (from Chicago to Los Angeles, later known as "Route 66") were part of this network. These routes became crucial arteries for cross-country travel, commerce, and later, American culture.
4. Foundation for the Interstate System: The 1926 U.S. Highway System laid the groundwork for the more advanced Interstate Highway System, which was developed decades later in the 1950s under President Eisenhower. Many U.S. Highways continue to serve alongside interstates, and some of the old U.S. highways are still in use today.

The year 1926 thus represents the beginning of a modern, structured approach to road travel in the United States, which revolutionized transportation and mobility across the country.

Building US-89 Through Glen Canyon: An Engineering Feat

Of all the federal highways crossing the Arizona–Utah border region, none was harder to build than U.S. 89 through Glen Canyon. The stretch running north from Flagstaff through Page, AZ and into southern Utah ranks among the most challenging road-construction projects in the American Southwest.

Canyon blasting was the defining challenge. Workers had to carve the roadbed directly through sheer sandstone canyon walls, requiring controlled dynamite blasts to open passage through terrain that offered no natural route. The geology of the Colorado Plateau — layered Navajo sandstone and Entrada formations — demanded precision work to avoid destabilizing the canyon walls themselves.

Extreme heat compounded every task. Summer temperatures in Glen Canyon routinely exceeded 110°F (43°C), making equipment failures common and limiting the hours during which crews could safely work. Paving operations in particular had to be timed around the brutal midday heat, which would cause asphalt to set too quickly or equipment to overheat.

Remote terrain created a logistical nightmare. The Glen Canyon region was accessible by almost nothing in the early construction era — no nearby towns, no established supply lines, no hospitals within reasonable reach. Every load of equipment, fuel, food, and materials had to be hauled in over rough desert tracks, sometimes for dozens of miles. Workers lived in remote camps for months at a time. The isolation meant that accidents — and there were many — often went without timely medical response.

The completion of the Glen Canyon Dam in 1966 and the rise of Lake Powell as a destination eventually made US-89 a critical corridor for tourism and commerce in the region, but the road itself stands as a testament to what it took to connect the canyon country of the Colorado Plateau to the rest of the nation.

US-89A and the Navajo Bridges at Marble Canyon

If US-89 through Glen Canyon was brutal to build, its alternate route — U.S. 89A — presented an equally daunting obstacle: crossing the Colorado River at Marble Canyon, where the gorge drops nearly 500 feet to the water below. This remote stretch of the Arizona Strip, wedged between the Grand Canyon to the south and the Utah border to the north, was one of the last roadless corners of the contiguous United States well into the 20th century.

The answer was the original Navajo Bridge, completed in 1929. At the time of its opening, it was the highest steel-arch bridge in the world, spanning 616 feet across Marble Canyon with a deck sitting 467 feet above the Colorado River. Building it required suspending workers and equipment over a sheer canyon void — with hand tools, primitive cranes, and no safety nets — in a location reachable only by rough wagon roads. Steel had to be hauled from the railhead at Flagstaff, over 80 miles away, across open desert and canyon rim terrain. The original bridge served as the sole vehicular crossing of the Colorado River between Moab, Utah and Needles, California — a stretch of over 600 miles.

By the 1990s, the old bridge was too narrow for modern traffic and showing its age. A new Navajo Bridge was constructed immediately alongside it, opening in 1995. The new span used the same steel-arch design but was built wider to accommodate two lanes of traffic. Rather than demolishing the original, ADOT and the National Park Service preserved the 1929 bridge as a pedestrian walkway — making Marble Canyon the only place in the world where you can walk across a historic bridge while watching traffic cross its modern twin just feet away.

Together, the two bridges are a vivid marker of how much — and how little — changed between the early construction era and today. The canyon walls, the wind, and the 467-foot drop to the Colorado are exactly the same. What changed is the equipment, the safety standards, and the century of engineering knowledge separating the two spans.

One of Arizona's Hardest Roads to Build: I-15 Through the Virgin River Gorge

The Virgin River Gorge section of I-15 is one of the most remarkable — and least-known — engineering stories in the entire Interstate Highway System. A tiny 29-mile dog-ear of Arizona that the state didn't even want to build, it became the most expensive rural Interstate highway ever constructed.

Why Arizona Didn't Want This Road

The politics here are as unusual as the geography. Despite objections from Arizona, which advocated placing the road two miles north of the gorge for cost reasons, the Federal Highway Administration insisted on routing I-15 along the Virgin River due to the scenic beauty of the canyon. Arizona was being forced to build one of the most expensive road projects in American history through terrain it considered unbuildable — for a stretch of highway that barely touched its own territory. The gorge cuts across just a 29-mile stretch of the Arizona Strip, a remote region north of the Grand Canyon that is entirely separated from the rest of Arizona. (AARoads)

When the Vietnam War caused federal highway funding to be cut in 1966, Arizona halted all work on I-15 through the gorge because the project had no real benefit to the state. Utah, which had already completed its connecting section of I-15 to the Arizona state line and desperately needed the link to California, advanced portions of its own federal highway funds to Arizona in April 1969 just to get the project finished. (AARoads)

What the Gorge Actually Looks Like

The Virgin River Gorge is a 15-mile-long canyon carved by the Virgin River through ancient rock layers over 500 million years old. Its walls rise up to 1,100 feet high, composed of layered limestones, sandstones, and sedimentary formations. The canyon floor drops an average of 70 feet per mile — ten times steeper than the Colorado River. (Grokipedia)

The canyon is so narrow and deep that the sun never hits some sections during winter months. Max Blazzard, the Arizona Highway Department's chief project supervisor, wrote at the very start of construction: "It's hard to visualize a divided highway in this area." Yet he led the team that built it anyway. (Arizona Department of Transportation)

Nine Years of Construction: What Workers Actually Faced

Construction began in earnest in 1966 and the last section didn't open until December 14, 1973 — nine years of work for 29 miles of road.

The geological surprises started immediately. During early building tests, a 50-foot-long pile was driven into what was thought to be bedrock — only to have sunk without a trace by the next morning. The riverbed was not rock; it was deep, shifting alluvial material that refused to anchor anything. The Virgin River was rechanneled twelve times during construction, moved out of the way to build, then moved again and again across the entire length of the gorge. (AARoads)

Rock blasting on the sheer canyon walls required engineers to rappel down 400-foot cliffs to place explosive charges. Bulldozers operated on ridges high above the canyon floor. Flash flooding was a constant mortal threat — a 10-foot wall of water surging down the canyon was not uncommon. Kiewit Construction anchored a metal barrel upstream: if it floated to a high-water mark it tripped a switch, and foremen in the lower gorge were notified by telephone that they had as little as 90 minutes to get men and equipment to high ground before floodwater surged through. (Arizona Department of Transportation)

Just getting equipment to the job site was its own ordeal. Kiewit pioneered a rough access road through the gorge that crossed the Virgin River 18 times. The company brought in 140 pieces of heavy earth-moving equipment, including 20 D8 Caterpillar bulldozers and 25 rock trucks with 50-ton capacity. Workers used 45 pickup trucks to move around the site, and the brakes had to be replaced on those trucks every six weeks from the constant strain of the terrain. The project superintendent later called it "the most challenging road project Kiewit ever had." (Arizona Department of Transportation)

The Price Tag That Broke All Records

When I-15 through the Virgin River Gorge opened in 1973, it cost more to build than any other rural highway on the Interstate system — $10 million per mile. The final 3.82-mile section of the Lower Gorge, where the canyon narrowed to as little as 150 feet wide, alone cost $13.8 million. This section held the title of most expensive Interstate highway ever constructed until the completion of the Big Dig in Boston. (Las Vegas Review-Journal)

Seven Bridges — and They Keep Needing to Be Rebuilt

Seven bridges carry I-15 over the Virgin River through the gorge, and maintaining them is an ongoing battle. The gorge is too narrow for detour routes, the canyon walls too steep for staging areas, and the river too environmentally sensitive to disturb. A recent bridge replacement faced exceptional challenges due to its location more than 80 feet above an active river, limited access, extreme weather, and a complete lack of viable traffic detour options. The solution used Arizona's longest single-span steel girders at 340 feet — a design that minimized river piers to reduce environmental disruption. Even rebuilding what already exists here requires inventing new approaches. (Engineering News-Record)

A Vital Road Nobody in Arizona Needed

Arizona's portion of I-15 is a 29-mile stretch with just three exits, none of which serve any major commerce. The state built the most expensive rural Interstate in American history for a road that primarily benefits California, Nevada, and Utah. The gorge belongs to Arizona, but the road through it is really everyone else's highway — a corridor that moves 1.4 million trucks per year between Las Vegas and Salt Lake City, threading through cliffs that were old before the dinosaurs. (Las Vegas Review-Journal)

Busiest and Longest Federal Interstates and U.S. Highways in Arizona

Arizona Designated Highways