Good article about the long road ahead for Christie, by Jeffrey Toobin.
"Ultimately, Fishman will probably give immunity to Kelly and Stepien, meaning that they will testify before a grand jury. At that point, they will be called before the legislative committee, because they won’t be able to take the Fifth anymore. By then, it will probably be summer at the earliest.
If there are indictments, they probably will not be issued until fall—and trials, if any, would be held in 2015.
In short (or rather, long), Chris Christie can look forward to many months of investigations. News leaks will abound.
Like most U.S. Attorney operations, Fishman’s investigation has been largely invisible to the public, but the legislators, especially the Democrats, live to embarrass the governor. And this is really the best-case scenario for Christie, one in which the investigators do not find anything that would seriously implicate him.
Events are now firmly out of his control. All Christie wants to do is put this whole matter behind him. It will be increasingly apparent that he has a long road ahead of him."
Bridgegate Will Be a Long Road for Chris Christie : The New Yorker
It also helps to explain about a little known term "act-of-production immunity" - which we will likely be hearing more about as the months drag on.