I've read/listened to the arguments against the short tunnel and feel clear it is a wrong course of action for the Stonehenge WHS given the damage it would cause. I cannot help but draw some comparisons with Avebury which has a busy road actually going through the stone circle itself - albeit not anything as busy as the A303. It would be unthinkable to divert or widen that road because of the damage it would cause. I hate to keep saying it but it is cars and the numbers of people using them that is the problem - a tunnel will not lessen the traffic or the traffic jams it will just take it out of view.
And then of course there is the cynical opinion that a tunnel would give EH/NT almost sole rights to the 'view of Stonehenge'.