Hi!
This might help.
27:14-26. Road closed temporarily; procedure
If the commissioner shall deem it necessary to close a road or section thereof being constructed, improved or repaired under this article, in order to permit a proper completion of the work, he shall execute, and file with the clerk of the board of chosen freeholders, a certificate stating the necessity for closing the road and describing the portion thereof to be closed. The board of chosen freeholders shall thereupon close it to public travel by erecting suitable obstructions and posting conspicuous notices to the effect that the road is closed. Not more than one mile of a road shall be closed at one time.
Or maybe this.
39:4-94.2. State, county or municipal highway, road or street closed with posted notice and barricade; violations; penalty
Whenever by order of the Commissioner of the Department of Transportation, a State highway, or by resolution of a county governing body, a county public road, or by appropriate action of the governing body of a municipality, a municipal street or road is declared closed to traffic for any lawful purpose, and a notice of the closing has been posted at the beginning and ending points of the closed section of the highway, road, or street, and a barricade erected at those points, any person who without the permission of the commissioner or governing body of the county, or municipality, as the case may be:
a. Mutilates or removes the notice, or damages, destroys or removes any warning sign or signal, or removes the barricade placed or posted by the commissioner or county or municipal governing body, at any point along the highway, road or street in connection with or relating to the closed portion thereof; or
b. Drives a vehicle over or upon the closed section of the highway, road or street which he knows or should have reason to know has been closed to traffic; or
c. Violates any rule or regulation for the use of the highway, road or street duly made by the commissioner or county or municipal governing body, as authorized by law, he shall be subject to a fine of not more than $100.00.
Check your ticket and see if one of these is what you supposedly violated. If so, you can ask where the barricades and notices were. Is the road still closed? Get pictures if it looks the same as it did. If you can, get some way of proving the date for the picture. If they had notices and barricades but there was still a space to get through that's different, but if all they had was a cop at the side of the road I'd say you have a pretty good chance.
I'd talk to a lawyer.