If you are going to enter Zion through the tunnel your senior pass does not cover the additional cost for this.
If you are in a MH or driving a dual wheel truck or just pulling a trailer they stop the traffic from both lanes and ask you to drive down the middle of the road through the tunnel.
It would be better to enter from the west side.
Its not only the tunnel but the sharp winding curves from the tunnel to the bottom of the canyon.
Hope this helps.
A couple of Mules
with a Covered Wagon