- Intrinsic differences: Real technical differences between bus (including trolleybus) and rail (including, it appears, things like monorails and rubber-tire metros);
- Misidentified differences: Differences which are related to propulsion rather than guideway type, or differences which arise from how specific lines are implemented in specific systems
- Cultural feedback effects: Difference which arise from a result of cultural perception, law, or custom.
1) There seems to be a quantifiable and measurable preference for rail over bus, at least in much of the developed world.
2) This preference may or may not be rational, may or may not be alterable (to the extent that planners ought to try), and may be conflated with issues dependent on local circumstances or practice, or who knows what else. (True apples-to-apples comparisons are often hard to make).
Given all of that, what should we (transit advocates, planners, decision-makers, or anyone else who cares about this) do about it, whether in planning individual lines or entire systems? Specifically:
- When and where should planners and decision-makers include modal biases in their forecasts (i.e. "a light rail line will attract X passengers per day, a BRT line will attract Y") and how much weight should these things be given?
- To what extent should transit agencies, et al, attempt to change these views?
There's another school of thought that holds that such biases ought not be considered, especially if they are likely to be irrational (i.e a survey states that 20% more riders will ride on rail than on an equivalent bus line, and the stated reason for that preference is that busses are slow and full of drunks), and that only good "hard" reasons for one choice or another should be considered, such as cost or technical parameters, and that "illegitimate" reasons for a preference ought to be given no weight. (This view is especially common when the reasons involved can be demonstrably reduced to racism or other forms of prejudice, which good public policy ought to oppose).
Some go so far as to suggest that modal bias (unjustified by tangible differences) is a problem that transit agencies ought to try and solve.
But these questions are ultimately political ones--decision-makers need to take all relevant factors into account. I tend to favor providing as much quality data as possible to decision-makers, and letting them handle the politics. (Not that they will necessarily do a good job here, but that is their job...) And while many non-intrinsic differences may be irrelevant in the abstract, they are often quite relevant in the context of a particular agency or system--if rail solutions gets signal priority at grade crossings as a matter of law whereas bus does not, or if a particular agency is not willing to add a new type of rolling stock to a fleet as part of a system expansion, these are important factors to consider. If there are changes for the better in the wider environment (cultural, regulatory) that can be made, then plan for those; but transit systems have to exist in a particular place.
And difference which are specific to that place can frequently be just as important as those differences which are universal.