Quote:
Originally Posted by fusili
This is what I disagree with. Time and money are not the primary determinants of travel behavior. Activity pattern is. How a household delegates activities, distributes resources and establishes priorities is much more important than time or cost. The guy who drives to work every single day, spends crazy $$$$ on parking and spends more time in traffic than using transit can only be understood if we also understand he's got a kid that might get sick at school and needs a ride home at a moment's notice. Understanding how this pattern is created is fundamental. Someone will drive to an activity that transit is faster and cheaper to do, just because they don't do it very often and couldn't be bothered to look into transit availability.
|
Well very much yes and also sort of no. I alluded to this above where I stated that activity-based modelling is the next step. But it's essentially an extension of the formulaton of discrete choice modelling as it's still based on individual decision making and often with utility albeit with more data. I'm not very up on my activity-based modelling, and not to say it isn't useful, but I doubt it will be leaving the halls of academia anytime soon. You'll find that much of the same people that were behind trip-based discrete choice modelling are behind activity based modelling. Time and cost remain very much a factor depending on what is being modelled. That being said, activity based modelling, while perhaps being a better representation of why people make trips (given travel is (usually) a derived demand), also might not serve to answer questions that you want answered. They tend to address scheduling, activity locations, etc. So it might not be helpful in a mode choice context - which can be tied to activities.
Quote:
|
And people don't make quasi-cost/benefit analysis for every decision they make. They generally create a activity and travel pattern early on, and then exhibit incredible inertia once that pattern is established. Nobody seriously wakes up each morning and calculates the time and cost of driving vs taking the bus. They just take the bus because they made that decision awhile ago. Housing changes and major job changes will shake up an activity pattern, but once it is set, it is difficult to change.
|
Yes, there is no question that this exists. We can continue on the many other things that can deviate from the "expected" but inertia for example is an implicit representation of a preference. Again, this is accounted for in these precisely because they understand that there is uncertainty.
I'm going to use the quoted scenario to illustrate why in the end an aggregate of the above is still, let's call it, useful.
Quote:
|
frequency matters less to the girl who takes a streetcar to go get groceries, because she can control the time when she gets groceries, or can move the activity to a different day. She can work the activity schedule around the transit schedule.
|
A transit agency wouldn't plan a frequency around what one girl prefers or does not. It does so around what the masses prefer. If willingness to pay for 1 min less waiting time is high enough on aggregate, the agency can choose to cut headway by 2 minutes. Or in the opposite direction, if an agency chooses to raise fares, by how much would they have to improve level of service, or how many patrons could they expect to lose. Where do you think elasticities come from? Again, you don't plan infrastructure or services for the extremes.
I can more than easily go on with the mathematics of it and the formulation, values of time for certain things and whatnot, but forget all this modelling, whether trip-based or activity-based. Taken inertia as given, the decision has or had to be made at one time or another. You don't think time and cost were the two largest factors for individuals on aggregate? What about when conditions change? People don't make route choice decisions on the fly when they hear an accident is up ahead, hence, expecting their generalized costs of travel to go up? What about the implementation of the Stockholm congestion charge? Some people felt it not worth paying for, they switched modes. In the longer run, they might switch activity patterns too.
But this is true for all decisions. You don't go to the supermarket grabbing things willy-nilly with no regard for cost or opportunity cost. The rich might I guess - luckily discrete choice models exactly can take that into account.
For the record, I'm skeptical of essentially all models. That doesn't mean they are all wrong. Just none are right.
Prev
:
Linear Mode
