I am writing a sentence and although what I am writing sounds right when spoken, it doesn't look right. Here's the sentence, in context:

We’re escaping just in time,” S.K. said with a smirk as if we were Bonnie and Clyde getting a five minute jump on police in hot pursuit. “This road’ll be a parking lot within minutes!”

I am assuming I can't put an apostrophe after road and add to l's and be grammatically correct, still that is the way people speak. Am I assuming correctly?
If one is being formal, one does not use contractions at all. One instead says "I shall", "he will", and so on.

But if you're being informal I'd say that'd be just fine.

Contractions are normally taking place for personal pronouns, aren't they ?

I'll, He'll, She'll, They'll ....... etc
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When you're writing with quotation from people, the rules often bend. This is so that real speech patterns can be faithfully reproduced for the reader. Often it is important to the writer that the reader get a certain feel about a character. In these cases, it's okay to "write like it's spoken". For an almost incomprehensible example, look at "Huckleberry Finn" by Mark Twain. The grammatically awful speech patterns of the characters are important to make the reader feel like he or she is in the deep south.

So your question is not about grammar really, but about writing style!

Short answer: I would say that "road'll" is perfectly fine in your case because you are quoting someone and it reflects their speech pattern.

As for narration, an anonymous narrator (a narrator whose identity you do not know), should never do this. Of course, if someone like Forrest Gump is narrating your story, that's different and the rules can be bent.
 rommie's reply was promoted to an answer.