Yes, it is possible. The road follows the river just like the lower river, close at times, more distant at others. Also, like the lower, there are places to park here and there where there is room to pull over on the side of the road but long stretches where the shoulder is too narrow. You will need to explore both the road for available parking, and then the suitable trails for finding the river. The middle river (between the crossing and Tamahi) has long stretches where private property makes river access more difficult, but there are lots of places to park and walk in, or you can drive up to Tamahi and take the backroad back down the other side. The upper river (above Tamahi) has more stretches close to the road but they are usually heavily fished, but you can hike in to the harder to reach runs where you might only have to share with one or two others.