On February 7, 2015 approximately 11:17 AM heading North on I 95 in Maryland my son spotted a blimp looking grey object in the sky. I was driving about 75 MPH at that time. My son who was in the rear passenger seat noticed the object. My wife was in the front passenger seat and my other son was in the back seat behind me. We all saw the object which appeared out of the passenger's side just over the trees. At first it looked like a miniature floating blimp you would see over a business to attract customers however, this object followed along I 95 north for about 7 minutes keeping up with traffic then slowing down then moving fast again keeping up with us. There were no visible mooring lines that you see on a blimp and there was no cabin below this object that you normally see under a blimp. The object moved opposite a blimp would move (wings first instead of wings following the nose of the blimp). Also, we did not notice any windows or writing on the object. What really caught our attention was how this object accelerated and was keeping up with us then went slower and accelerated right back parallel with us. As we traveled along I 95 North, the object moved out of our sight. We were not sure where the object had gone as trees were in the way. My son took pictures and a video. I attached three pictures. Two pictures were at regular distance and one picture zoomed in. We also took video of the object at regular distance (I apologize the video is downloaded sideways). If anyone knows what the object may be, please let us know.