Careless Driving After a U-Turn and Accident

Hi. I was in an auto accident recently in new jersey. I needed to go to a post office on the other side of the road. There was a u-turn a little after the post office, almost diagonal from the entrance of the post office. I took the u-turn, waited, saw that there was no vehicle coming and crossed the two lane road to enter the post office. I was almost inside the post office when i got hit from behind by a car in the right lane. My car spun 180 degrees and my bumper was damaged. My car inner tire had already turned and the car outer tire was almost in the outer edge of the right lane. The road speedlimit was 50mph of the road I crossed. The police officer said that the other vehicle had right of way and so it was my fault. Also, as the u-turn was close to the post office entrance, I should not have taken it and it was careless driving. He said it doesnt matter if the other car was speeding in the right most lane. Is he right?

My contention is that there were no solid lines on the road and no signs prohibiting us from taking the u-turn and driving into the post office. In fact, we saw atleast 2-3 cars do the same that day. I had stopped and checked before crossing the road. I was in the right most lane and the car that hit me appears to have been speeding in the right most lane. So how is my driving careless? Is my argument acceptable? If the people in the other car are injured and if the court thinks i'm guilty of careless driving, can they sue me for personal injury? They were walking around and waiting for the police so there was no serious injury. But they did go to the ER.

Please let me know what you think.

The issue isn't that a U-turn is prohibited at that location. The issue is that due to the angle, you had to cut across multiple traffic lanes to turn into the driveway. That's not something that oncoming traffic is reasonably going to anticipate.

Where did the other vehicle come from?