I will offer my thoughts, but I am not the best in spelling,punctuation and grammy. I would say to capitalize it as it is part of the name of the road. "Interstate 70 runs near my house, I travel on the interstate daily."
I agree with SeverinR. Capitalize the specific name (They followed Interstate 66 as it cut its path neatly through the mountains of Northern Virginia.), but lowercase the mentioning of an interstate (They took the interstate to the hospital.).
ditto both of those replies... lost guy... since you need so many questions answered, i'm wondering if you have a good punctuation guide and a strunk & white kept handy... if not, you should get them, as no serious writer would be without the 'tools of the trade'... you'll find my list of 'tools' in a sticky somewhere on the site, if you need recommendations... and a list of online references, as well... it would save you [and us] a lot of time and effort to keep them at your side...
In this case, the interstate is being referred to in dialog, so I guess i would have to say "Interstate Seventy-Six"? Sorry for the three threads. I have CMOS at home, but I can't always find precisely the subject in the index. For the colon question, some of the instructions (the capitalization after colons) are a little too confusing with the exceptions. For this one, I wasn't sure where to look at for interstates. And for the rambling one, I didn't think CMOS had a section that covered that and I just wanted to get some opinions. I'll go easy on you guys from now on.
Well, most numbers in dialogue are spelled out, but it is not required of all. To me, it's usually deciding whether the number is more important or if the way it's said is. So yes, "Interstate Seventy-Six" or "Interstate 76."
I totally agree with you on that logic. Sometimes the slowness of reading a long number doesn't justify how it's said, but I was told to spell numbers out. My understanding for numbers is that we should spell it out unless the number is too bulky to spell out--years, for instance--if it's a recognizable title--Fahrenheit 451, The Jackson 5, Rocky II, Kiss's Alive III, Boyz II Men, 1984 (although one of the accepted spellings is Nineteen Eighty-Four, which makes that example moot, anyway)--or if it's a combination--vitamin B12. But all other numbers should be spelled out, according to what I've learned. Wasn't sure if "Interstate Seventy-Six" constituted a title, but I figured I'd play it on the safe side.
i don't recommend relying on the CMS for writing fiction... this article pretty well spells out why: http://deannahoak.com/2011/03/29/cms-novels-and-formal-writing/
