I support you staying off the heavily trafficked roads – cars are no fun.
Ride your rolling terrain for this session and choose the hilliest route you have available. Ride mostly on a 2:1, zone 2-3:zone 1 ratio. So if your climb is 5 mins in power L2-3, take 2.5 mins in L1 after. A 2 min hill in L2-3, take 1 min in power L1. You don't have to be exact as I'm sure every hill is not exactly symmetrical but that is roughly the sequence you are aiming for to pull off this session with the terrain you have available. A geared bike will make staying in the target zones more doable than a SS.
Lynda