Add BRT/bus priority flag to highway links, rather than relying on future bus coding for all TTF=2 coding?

[nmpeterson]

Currently, any bus routes that have bus priority along any portion (i.e. require TTF=2 in Emme) must have full coding in the bus_future_itin table. This is true even for existing bus-priority service (Pace's bus-on-shoulder routes, CTA's Jeffery Jump and Loop Link routes), where "future" routes are coded to replace the imported GTFS-derived routes.

Coding bus routes is extremely time consuming, error prone, and completely unresponsive to changes in existing routes that are being substituted out. It seems to me that a more elegant solution would be to assign bus priority to specific links in the network (both the base network and highway project coding), and assume that any buses using those links should have TTF=2 in Emme. Since some bus priority is time-specific (e.g. parking lanes becoming bus lanes during peak periods), it may make sense to code this using "TOD"/time-of-day strings like the future bus routes currently use to specify coding for specific model time periods (e.g. "234678" for AM and PM peak, plus shoulders).

This would make it significantly easier to code many BRT projects in the future, where existing routes become more efficient. Only new routes would need to be coded, and changes to existing service would all be handled by simple highway project coding.