No simple maths. If due to delays a lorry can only do 2 journeys in the time taken to do 3 journeys previously, to do the same number of journeys you need more lorries. The number of journeys across the water remains the same, hence no need for more ferries but an obvious need for more lorries.Flawed logic methinks, more lorries to join the ever increasing queues unless something is done to relieve the bottleneck