50 States, 50 Ways to Move, Stop 3 of 50
Remember Chapter 4 of my Research on Transport series, where the Greek stadion measured 192 metres in one city and 177 in another? Humans have always struggled to agree on a ruler.
Arizona is where America once tried to change its own. In 1975, Congress passed the Metric Conversion Act, and one of the first decisions of the new Metric Board was to turn a nearly finished Arizona highway into a pilot project. The highway was Interstate 19, and its signs have shown distances in kilometers ever since.
The Road Network
These figures are from the Federal Highway Administration (FHWA), Highway Statistics 2023.
- 75,224 miles of public roads: 43,603 rural and 31,621 urban.
- 1,164 miles of Interstate: 914 rural and 250 urban.
- Those Interstates are only about 1.5% of Arizona’s road miles, but they carry about 22% of all driving.
- The state highway agency owns 6,853 miles, about 9% of road miles, and those roads carry about 49% of daily vehicle travel.
The Travel
In 2023, vehicles in Arizona traveled 75.3 billion miles. That is a little more than Alabama’s 72.3 billion, on about three-quarters of Alabama’s road miles. About 76% of the driving happens in urban areas (FHWA, Highway Statistics 2023, Table VM-2). Arizona’s roads are fewer, but they are busy.
The Commute
In 2024, 67.5% of Arizona workers drove to work alone, against 69.2% for the US. Arizona ranks twelfth lowest in the country (US Census Bureau, American Community Survey 1-year data, 2024). Alaska was at 66.8% and Alabama at 80.8%.
Safety
Arizona recorded 1,304 traffic deaths in 2023, down slightly from 1,320 in 2022. Of the 2023 deaths, 429 (33%) involved an alcohol-impaired driver (NHTSA). The Arizona Department of Transportation (ADOT) also reports 258 motorcyclist deaths in 2023, the highest figure in at least 20 years.
The Bridges
Arizona has 8,590 bridges in the National Bridge Inventory (FHWA, 2026 release):
- Good: 5,378
- Fair: 3,120
- Poor: 92, or about 1.1%
That is one of the lowest shares of poor bridges in the country, compared with 3.3% for Alabama and 7.6% for Alaska.
Rails and Light Rail
Two Amtrak long-distance trains cross Arizona. The Southwest Chief, running between Chicago and Los Angeles, crosses the north every day, stopping at Winslow, Flagstaff and Kingman. The Sunset Limited, between New Orleans and Los Angeles, crosses the south three days a week, stopping at Tucson.
In the Phoenix area, Valley Metro Rail opened a 20-mile starter line on December 27, 2008, linking Phoenix, Tempe and Mesa. It has grown to about 35 miles and carried around 11 million riders in 2025.
The Highway That Speaks Kilometers
Interstate 19 runs 63 miles from Tucson to Nogales, just short of the Mexican border. That is 102 kilometers, and the signs say so. Distances to exits are in meters, and distances to towns are in kilometers. Only the speed limit signs stayed in miles per hour. ADOT calls it the only highway in the United States fully marked in kilometers.
The idea of changing back has come up, and the people who use the road have pushed back each time. A highway the country meant to be an experiment became a local landmark.
The Highway Animals Can Cross
Arizona’s cleverest trick is helping wildlife travel safely. On State Route 260 east of Payson, ADOT and the Arizona Game and Fish Department built underpasses and bridges for elk and linked them with fencing that guides animals to the crossings. Elk-vehicle collisions dropped 98% over six years, according to ADOT. More than 15,000 crossings by 16 species were recorded at six underpasses over seven years.
Near Hoover Dam on US 93, three overpasses built for desert bighorn sheep opened in 2011, and more than 4,300 sheep crossed them in the first two years. The Alabama way was to reverse a highway for people. Arizona’s is to build a road for animals.
Next stop: Arkansas, the Natural State.
Sources: FHWA Highway Statistics 2023 (Tables HM-20, HM-81 and VM-2); NHTSA, Overview of Motor Vehicle Traffic Crashes in 2023 (Table 9); Arizona Department of Transportation, 2023 Motor Vehicle Crash Facts and published articles on I-19 and wildlife crossings; U.S. Census Bureau ACS 2024 via America’s Health Rankings; FHWA National Bridge Inventory 2026; Rail Passengers Association, Amtrak in Arizona fact sheet.