One of the reasons it might seem a bit dated is that he originlly wrote and published it in the late 70s. It was then re-released as an unabridged version in 1990, with a few changes by King - namely changing the dates from 80s to 90s, and adding in a few pop culture references.
How long did it take the guy right at the beginning to die (Campbell, was he called?)? It was a matter of hours, wasn't it? Most people would carry on driving if they had a cold, and with something that's as quick as Captain Trips, it would lead to them all dying in their cars. I suppose that the mass exodus would have caused traffic jams, too, which would have meant a lot of people would have been in their cars for much longer than usual, too.
I know what you mean! I've read it twice, and both times I've had a cold!! Scary stuff, ain't it?