MileCheckWe don't condone stealing mile markers. They're how crews, troopers and dispatch find you.
The short answer is the number. 420 is cannabis slang, and a sign that says 420 makes an easy souvenir. Highway departments get tired of replacing them.
Which DOTs swapped the number?
Colorado. Around 2013, the Colorado Department of Transportation put a sign reading 419.99 on I-70 where mile 420 had been. A spokeswoman told reporters it seemed to be working, but predicted the attention might get the new one taken too. NBC News
Idaho. In 2015, the Idaho Transportation Department replaced the mile 420 sign on US-95, just south of Coeur d'Alene, with one that reads 419.9. An ITD spokesman said it was the only 420 sign the department had changed, and that crews already spent more time mending signs than replacing them. Boise State Public Radio
Washington. At theft hot spots, the Washington State Department of Transportation has moved the marker back a tenth of a mile and relabeled it 419.9. Sometimes it leaves the spot blank, so drivers see 419 and then 421. A 2019 report counted about 8,245 mile marker signs on state highways, with almost 200 missing. The Inlander
One roundup of all three is at Equipment World. We did not find a newer report on whether the 419.9 signs are still standing.
Why do so few states have a mile 420?
Mile markers usually start over at zero at each state line. A route has to run more than 420 miles inside one state to reach the number. Most don't.
We checked the mile marker data built into MileCheck. About 14 states have a mile 420 on at least one road in that data. About 37 have none.
Two cases need an asterisk. California numbers its signs in postmiles that restart at each county line, so a bare "420" doesn't point to one place the way it does in Colorado. Texas uses reference markers, which are not true mile counts, so Texas shows up on many roads. A TxDOT reference marker 420 is not the same thing as being 420 miles along the route.
States with a mile 420 on a road
One main route per state is listed. Many states have several.
| State | Route with a mile 420 |
|---|---|
| Arizona | US-191, US-89, US-180, US-160, SR-61, SR-264 |
| Colorado | I-70 |
| Idaho | US-95 (the 419.9 sign), US-30 |
| Kansas | I-70 |
| Louisiana | LA-1 |
| Maine | US-1 |
| Montana | I-90, US-2 |
| Nebraska | I-80 |
| New Mexico | US-64, US-70 |
| South Dakota | US-14, US-18 |
| Tennessee | I-40 |
| Texas | I-10, I-20, I-35 and many others (reference markers) |
| Washington | SR 12, SR 20 |
| Wyoming | US-287 |
A few more roads are long enough to reach 420 even though our data skips that exact post. I-75 in Florida is about 471 miles long, and I-40 in North Carolina is about 420 miles long, ending near Wilmington. I-25 in New Mexico also runs to about mile 460 in our data. This table is a first pass and not a complete count.
Where to read more
Colorado's I-70 is the best known case. See the I-70 corridor and Colorado road conditions. Idaho is at Idaho road conditions. For how the numbers work, see how to find your mile marker and mile markers in Washington.
If you want a sign anyway
Some DOTs auction retired signs. Wyoming sold 21 retired "Welcome to Wyoming" signs in 2025 through its surplus site, according to Cowboy State Daily. We did not find a state that sells retired mile markers, so check with your DOT before you bid on anything.
We don't condone stealing mile markers. They're how crews, troopers and dispatch find you.
If you want your own mile marker without the sign, MileCheck shows your nearest one on your phone, down to a tenth of a mile.