The A20 connects Folkestone and Ashford. The "A" roads are national routes or what would be called state roads in the U.S., though the A20 is not one of the larger ones, having just two lanes. The route from Ashford to Folkestone is far from a straight line, as you can see on Riddley's map: the A20 meanders over hills and around farms—crossing and recrossing the straight 6-lane express monster of the M20.

One might ask why Riddley did not take the M20; there's no sign of the M roads on the map, and Riddley doesn't mention encountering any ruined overpasses. Either the M20 was built after 1980, or Hoban wished it out of existence for understandable aesthetic reasons. [EB]

(Probably a bit of both. The CBRD Motorway Database gives a timeline: the Ashford-Folkestone section was opened in 1981, but it would have been visibly under construction in 1980. [RG])