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Comment by Sanddancer | Hacker News Reader

There's another rule this one doesn't touch. Route numbers that are divisible by 5 are considered major routes, and with a few exceptions go from one geographical extreme to the other -- Interstate 5 goes from Canada to Mexico, Interstate 80 goes from San Francisco to New York.

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> Route numbers that are divisible by 5 are considered major routes, and with a few exceptions go from one geographical extreme to the other

They tend to be major, but only 11 of 19 (11 of 17 that exist) go from one geo extreme to the other. Sorry highway numbers are a hobby of mine (yes I know strange hobby).

5 ^: Mexico to Canada

10 ^: Pacific to Atlantic

15 ^: Mexico to Canada

20: Mid-Texas to Mid-South Carolina

25: Southern Texas to Wyoming

30: Texas to Arkansas

35 ^: Mexico to almost Canada

40 ^: Eastern California, to Eastern North Carolina

45: Entirely in Texas

50: N/A

55 ^: Gulf of Mexico to Great Lakes

60: N/A

65 ^: Gulf of Mexico to Great Lakes

70: Utah to Maryland

75 ^: Southern Florida to northern Michigan

80 ^: San Francisco to New York

85: Mid-Alabama to Mid-Virginia

90 ^: Seattle to Boston (longest in the country)

95 ^: Maine to Florida

Why are 50 and 60 excluded? Wikipedia seems to think they exist, but it could be wrong.

They were skipped for unknown reasons. US Highway 50 and 60 exist though. Could possibly be why. An Interstate 50 and a US 50 in close proximity would be...confusing.

Us highways 50 and 60 exist and the location of Interstate 50 and 60 would be kinda close to where US-50 and 60 are, so they were probably skipped to avoid confusion.

When the Interstate Highway System was first created, AASHTO had a rule that no Interstate and US Route with the same numbers could coexist in a state. Since with both numbering schemes, 50 and 60 would fall in roughly the same part of the country, I-50 and I-60 had to be skipped so they wouldn't share any states with Route 50 and Route 60.

AASHTO has since relaxed that rule, and there are now a few exceptions to it, but it's too late to shoehorn in two major interstates.

AFAIK, the old US Highways were numbered opposite to the Interstate system, at least for round-numbered routes. US-10, 20, 30, etc., more or less proceeded north to south, Interstates are increasing south to north. The middle numbers like 50 would possibly overlap in both systems so designations like I-50 weren't used.

Indeed they are. Route 1 mostly runs along the east cost (key word is "mostly") often next to I-95, and Route 99 used to exist right next to where I-5 is now (it's since been turned into a gaggle of state highways in CA, OR, and WA), while Route 2 runs in the north and Route 90 largely runs next to (or is co-signed with) I-10.

Yup, in fact there are 99W and 99E more or less straddling I-5 and running in generally north-south alignment in the Portland metro area. In recent years I-5 has become increasingly congested, not just in "rush hour". Consequently 99E/W are also heavily used as commuters try to escape traffic. Hard to solve the problems created by our success.

You ever get a twitch in your eye when you see I-238?

Every time.

99 is a real tearjerker too

I-69 and its three branches (69W, 69C, 69E) in Texas always gets an emotional response from me.

At some point decades from now, it won't be quite as bad because all the different segments of I-69 will be united. We'll still have a weird three-way split in South Texas, but north of the split they'll form a single highway going all the way to the Canadian border instead of the current disjointed highway segments. And there are parts of the country where I-69 fits in between I-65 and I-75, so while the name is awkward in Texas, that's not the case in the Indiana and Michigan.

But this will take decades due to limited funding and a bunch of states that just don't care. I'll be lucky to see it in my lifetime, and if I do, I'll be an old lady.

What weirds me out in that area, by the way, is that I-2 even exists. I grew up understanding that I-4 was the lowest-numbered Interstate in the country (and my family went to Florida often enough when I was a kid that I was quite familiar with that road), and it still hasn't quite sunk in yet that it got dethroned.

I-99 is particularly aggravating because of how it came into existence. At least I-238 exists by necessity. I-99 has its number because a showboating Congressman snuck the number in as a rider on a bill because he thought "highest possible two-digit interstate" would get his state some more tourism.

As such, I-99 is the only interstate AASHTO is forbidden by law from renaming.

I-40 is an interesting case. It hits the ocean in Wilmington NC, but doesn't make it to the coast in California, ending in Barstow. The completionist in me says that it ought to continue through Palmdale to Ventura.

Until a few years ago, it wasn't contiguous. There was a gap in Memphis where the locals objected to its completion because the traffic noise would have disturbed the animals at the zoo. So the northern part of I-240 was signed to include I-40, finally linking the two halves together.

Caltrans has a long-term plan to get I-40 extended to Bakersfield. It's probably not going to ever quite hit the ocean because the Coast Range west of there is pretty rugged, and the traffic continuing through is pretty minimal.

I agree with you on that one. I debated whether to count it as going from one extreme to the other since it stops about 150 miles short of the ocean, but I figured since it gets you most of the way, might as well count it.

> There was a gap in Memphis where the locals objected to its completion because the traffic noise would have disturbed the animals at the zoo.

A bigger reason is that the road would have run straight through Overton Park and required that the entire park be destroyed. People like Overton Park, and the protests over that got the project cancelled. In fact, they actually built the road east of Overton Park, but they stopped there when the protests started. What was intended to be I-40 is now called Sam Cooper Blvd. If you look at Google Maps, you'll see that the gap between the end of I-40 on the west side and the beginning of Sam Cooper basically just consists of Overton Park and a few blocks in each direction.

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