Interesting...
Although some of its routing is curious.
Colchester to Ramsgate (both Roman towns - Camulodunum and Rutupiae) takes the Roman road (now the A12) into London, but for fastest route then takes a boat down the Thames and along the Kent coast to reaching Ramsgate, despite the well known Watling Street being available from London (A2).
Maybe they heard about the queues at the Blackwall tunnel!
Anyhoo...If the boat really was that much quicker than the roads, surely walking from Colchester to West Mersea or Clacton and just taking a boat straight down to Kent would be far quicker than walking into London and back out again?