It transpired that maintenance work was being carried out on the bridge and that traffic travelling south would use one of the two tunnels which each have two lanes.
Crossing from one side of the road to the other only has a single lane. Hence, we had all been squeezed in to one lane to make the crossing and then immediately expanded to two to go through the tunnel. Why had they not created two lanes to cross to the other side meaning twice the traffic flow?
"Don't think of them as problems, think of them as opportunities."
"OK, I think I've hit an insurmountable opportunity!"