(Nodes,Nodes,Household,Member of the household,Trip, Autos) expansion is how many trips this particular trip would represent in reality. In this dataset all of them represent 20. a(minutes) and b(minutes) are the bounds of the time window to do a trip, meaning the earliest departure time and the latest arrival time at the destination. This is based on the travel time. They can be realaxed. You can interpret a as desired departure time and b the desired arrival time at the destination. 