Add a new subrule to the rule “Routes”, called “Jam”:-

A Jam Route has a Scouting Cost of 4. When a Driver drives a Jam Route, that Driver earns 2 Cash. Immediately after Driving a Jam Route, the traffic jam spreads - the Driver must change the first Route in his or her pool to a Jam Route.

Reword the final paragraph of the rule “Routes” to:-

Twice per day, but not more than twice in any 12-hour period, a Driver may either Drive or Avoid the first Route in their Routes pool. This moves the Route to the bottom of the list, makes it Inactive, and, if that Route was Active and the Driver did not Avoid it, causes them to get the effects, if any, described in the subrule corresponding to that Route.