You might have some grounds to take action against the agent for failure to disclose if you could prove that they were intentionally withholding the DA from you, or ought to have known about it. If so, the fact that they remained silent when you asked the question may give rise to a negligence claim. The fact that they gave you other materials should help establish that they had, or at least assumed, a level of duty of care. This will be contrasted against you not seeking your own advice, however.
The long and short of it is, however, that it doesn't look like you're going to get out of the requirement to build the road.