Driving up to Traverse City from where I live in Kalamazoo, (yes, it is really a city) I started wondering: What is the difference between an Interstate and a US Highway?
I believe interstates do not have red lights. Highways do.
Interstates have egree and entry only through ramps (Exit 7, 100B, etc.), whereas U.S. Highways have crossroads, as jacksen9 said.
Interstate Highways are part of the Interstate highway system, which started in the 1950s (note the signs naming them for Eisenhower). They are all limited access highways, often built specifically for that purpose (though the system sometimes includes state-built highways like the New York State Thruway or Massachusetts Turnpike).
US highways are older. They are often not limited access.
Hmm, the Highway I was on (US 131) had no traffic lights and had no roads crossing it at the same height. Is 131 just an anomoly in the world of highways?
The principal difference is which pot of money the state and Federal governments use to build the highway.
I don’t think any new US highways are being built, although there are new stretches of Interstates.
The Interstate highway system only dates back to 1956. The US Highway system started in the 1920s I believe.
A US Highway can be controlled access, with no other roads crossing at the same height, but it does not have to remain that way. The same goes for state highways. GA400 runs near my apartment. If I get on and drive north, it is controlled access for 30-40 miles. After that point, it becomes a regular road, with traffic lights and roads crossing it, but it’s still GA400.
An interstate is always controlled access (I believe). I’m under the impression that there are specific rules for when a highway may be designated an interstate. I’ll hunt a bit and see what I can find out.
Oh, wmulax93 , welcome to the board. 
Not at all. Any US highway can have stretches where there are no crossroads (as opposed to the exit ramps). But most importantly, the state highway is only known by its name in a particular state. For example, we have a Route 301 that goes along Maryland’s Eastern Shore. Now, this highway can cross into other states - Delaware, Pennsylvania - and will then be known under that state’s own numbering system, say Delaware Route 299 or something. Interstates, on the other hand, always go from state to state (ok, Hawaii’s highways are an exception), carrying the same designation throughout their run.
You’re attempting to impose rules that don’t exist. RealityChuck has the right statement - Interstate highways are part of the designated “Interstate Highway System”. US Highways can retain names across state boundaries, and can be limited access, and many of them will concide with parts of the Interstate system along various stretches. And while most Interstate highways cross state boundaries, there are some in places other than Hawaii that do not (and not just the 3 digit urban ones).
Examples: US 50 crosses Kansas, Colorado, Utah and Nevada. For a small part of CO and about half of UT it coincides with I-70. US 101 is limited access for a large part of its jaunt through CA, and is not an Interstate. I-17 stays entirely in Arizona.
dantheman, I think you’ve confused state highways with the US highway system, I think. US highways, like interstate highways, also maintain their designation for their entire routes. Find a road atlas and follow US 1 from where it starts (as far as I can tell) at the US/Canada border town of Frenchville, Maine, all the way down to Key West.
Oh, and the OP may want to check out this page. Scroll down a bit to “Interstate Highways.”
Addendum - do not confuse the “US Highway” designation, which crosses state lines with state route designations that can, once again coincide with US Highways. Rand McNally shows US 301, for instance, consistently numbered across Delaware, Maryland and Virginia. Since state routes in those states, as well as other US Highways coincide with it over various stretches, I will concede that the signage placed on it might wind up seemng, well, whimsical. Not having driven on it, I don’t know for sure.
This is one of my favorite subjects of all time.
1- and 2-digit numbered US Highways are generally done under a numbering system where the even highways run east-west in numerical order from north to south and the odd highways are run north-south in numerical order from east to west.
The 1- and 2-digit interstate highway system is also even east-west but runs numerically from south to north and odd numbers are also oriented north-sourth but in numerical order from west to east. There is a point in the country therefore where things get pretty confusing, just about in the middle.
All interstates are controlled access. US Highways can be either way and often switch back and forth from controlled-access to direct intersections.
Three digit highways on the interstates are uniformly related to the major interstate in the last two digits (i.e. 355 is related to 55). Generally an even first number corresponds to a bypass while an odd first number corresponds to a spur or trunk. This isn’t always the case anymore. I can think of one glaring exception in US 476 in PA is basically a spur highway from the PA Turnpike (I-76) to the poconos, though it also connects to a bypass around Philadelphia.
Speaking of exceptions, there is a drawbridge on I-75 north of Toledo in Michigan with a stoplight. It is the only stoplight I have ever seen on an interstate. Of course, not all interstates are freeways (in that some are tollways) so controlled stopping on an interstates happens otherwise. Other than that drawbridge and the tollbooths, I have never seen a mandated stop on an interstate (indeed it is illegal).
US Highways are a bit more creative in that they can be whatever they wish to be. Sometimes they make right turns at intersections. Many do not bypass towns but barrel on through them. In that way, they are often more intersting to take than the freeways. There are also a whole lot more of them and they more often fail to follow the patterns I outlined in the beginning of the post. Moreover, the three-digit US highways are not related to the last two digit highways in the least.
Contrary to the tone of dantheman’s post, US Highways maintain their numbering across state-lines. This is different from state-highways which change their numberings. However, there is more state control of the US-Highways than there is for the interstates, and more often than not the state and US-Highways end up under the same state DOT management. The federal subsidies are generally more for the limited access interstates that are freeways (though the lines get blurred more and more as time goes on).
A further note on signage… the US Highways and the Interstates each have their unique shields that you can see examples of them here. State highways are designed by the state. For example, they are a keystone in PA, the shape of Ohio in Ohio, etc.
I can’t resist: county highways are also designated by state mandate most often. In most states they all have a consistent shape that is different from the interstate, us highway, and state highway signs. They are often numbered by county with the peculiar exception of Wisconsin which uses letters to designate their county roads!
And that’s the story of highways.
JS Princeton - “I’ll take interstate / highway trivia for 200”
I remember reading that there is a stoplight on I-76 in Pennsylvania somewhere between Harrisburg and Pittsburgh. Does anyone care to refresh my memory?
In a thread a while back we discussed the fact that there are Interstate highways in Alaska, even though they are not marked as such and are generally two-lane roads. http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=103760
There’s also a stoplight on I-95 at a drawbridge near Washington, D.C.
There are no stoplights on 76 (PA Turnpike) between Harrisburg and Pittsburgh
Wow, what a great response. Thanks everyone for all of the help.