The width would be *5'. He said he wanted something 15' long, so I was thinking two @ 8' long. It's to start a road so the trucks can get off the road without sinking in the ground. Half the truck would be on pavement, and the other half on mats. This is one project use, then maybe for whatever on the farm if the need comes up. It would be pine cause that's what I have immediately. It also shaves a bit of weight for handling with a bobcat. I might be able to do red oak, but I'm not sure I have enough immediately available.
*After saying 5', I was thinking 4.5' might work out better. I could do 4 lengths @ 12" each, then a spacer in middle at 6", which would allow me to insert a bar at each end with a pocket for lifting with a sling.