From @zneedell

Basically if someone has a set of trips (e.g. home -> work -> eat -> work -> home) and no pre-determined modes, I think it would be great for us to totally clarify what mode options the agent has for each of their trips depending on what their first mode choice is. I think right now, if they choose CAR for their first trip they are locked in to CAR for every trip until they go back home, which I think is OK for now. But is that the case if they choose walk? E.g. they should be able to WALK to work and then take ride-hail home because they don't have a personal vehicle with them. I think it would be great to clarify what the logic currently is for these different combinations and then figure out if we want to make any changes. E.g. one nice change that we could make is if someone takes their car to work in the morning, they should still be able to choose walk for the work -> eat -> work trips (aka subtour) because they know they will return to where their car is parked before coming home. But that logic might be a little tricky to implement in all cases.

The current logic is

• When a person has chosen the Mode they stick with it until they get Home or a Replanning happens.
  So if a person has chosen Walk they use this mode until they get Home. But if a replanning happens the may choose Car at work and get Hobe by a personal car which is also not quite right.
  

OK thanks--so yeah, I think it's worth exploring whether we can make currentTourMode not automatically determine the mode of the rest of the trips until they get home, instead for it to just constrain the available alternatives. Here's an initial proposal:

• If the initial trip is CAR: all trips need to be by car. (we could make this more complex by saying they can choose other modes for a subtour as long as they return to the car's parked location before returning home, e.g. home->work->eat->work->home, but let's ignore that for now)
• If the initial trip is by a private BIKE: Same as car
• If the initial trip is walk-transit, walk, ridehail, or shared vehicle: They can choose any mode for subsequent trips (except for private car or bike, although we'd expect those not to show up as alternatives based on what is returned from the household vehicle manager.
• If the initial trip is drive-transit: like above, except the last trip returning home must be drive-transit

How does that sound to everyone (including @haitamlaarabi , @wrashid , @nikolayilyin , anyone else)?

One addition--I think we might want to change how currentTourMode is used. As I understand right now we're treating it like current trip mode (e.g. it's what the agent looks to to uniquely determine the mode of an upcoming trip), but really it's something that should be set for all trips on a tour when someone leaves for the tour, but rather than determining the mode for individual trips directly it should implement the logic above on constraining the modes.

Generally, I agree with what @zneedell says. But we need to remember that CAR (BIKE) tour includes shared cars (bikes). So I think that we can simplify these rules (but have the same result) by using currentTourPersonalVehicle field that is supposed to be used this way.
In this case, we could always choose any mode for subsequent trips (or take the mode that is defined by the plan) but if the currentTourPersonalVehicle is set then we need to use it.

@zneedell AFAIR you took over this task. If you didn't please reassign it to me.