I was on I-70 headed east towards Greenfield where I live. I frequently stargaze and look out into the sky on my drive home at night so I am quite accustom to what is normal and what is not, especially after my other black triangle encounter in Greenfield on April 6th, 2011. I saw a bright light off to the north east and initially thought it was a satellite. But I could see it moving past the stars at a quicker pace that made it definitely not be a satellite. It emitted a bright white/yellow light. I got closer to it, it was on my left above some field. As I got closer it stopped it's very slow hover and began to cruise west at slow pace. I was able to compare it's speeds to other cars headed west. They were traveling somewhere between 45 and 70 miles per hour depending on if they were speeding or not. The cars were beating this thing, it was obvious it was moving very slow. It looked to be about 8-12 stories high in the sky compared to the light posts along Interstate 70. It was silent, or at least I could not hear much at all traveling at interstate speed. As I became parallel to it there was no longer a bright light on the front of the ship. It had green and red lights on starboard and port side, and was a very flat object. It had blinking white lights on the bottom/side of the ship. If you read the other report for the event that happened on April 6th, 2011 then you can tell I am describing similar ships/planes. I was very interested as this is my second encounter with a very similar type of craft. I was not scared, just extremely interested. I lost sight of it as it headed west and I was headed east. My phone was dead unfortunately and was unable to get any media of it.