Mass Ave / Central Sq in Cambridge
In March 2018, Ari posted updated thoughts on Mass Ave from the Charles River through Central Sq
Cambridge is planning to do a quick build reconfiguration from Memorial Drive to Sidney St at some point in the next few months.
Looking at Ari's visuals has helped me to better understand how that arrangement for Central Sq might work, and I'm thinking it's worth carefully considering at some variations.
Immediately west of Sidney St in the Lafayette Sq area, I think the Harvard bound bicycle lane would be better protected if it stays on the outside instead of moving to the center; the fire station driveway means that the center of Mass Ave can't be obstructed by a well protected center bicycle lane there. Additionally, Ari writes about a 75 second cycle time for the Sidney / Mass Ave light; I think it would be better to try to come up with a design where no light has a cycle time longer than 60 seconds at times when no bus or fire truck is around (I think it's probably OK if transit signal priority and emergency vehicle priority triggers longer cycles), and so putting the outside bicycle lane to center bicycle lane crossovers at relatively simple intersections instead of Sidney is probably desirable.
The arguments Ari's March 2018 blog post makes for the center bicycle lanes focus on the Red Line headhouses and bus to subway transfers; I think those arguments are pretty compelling for the Pearl St to [edit: Prospect] segment, and perhaps also a bit to the west of [edit: Prospect], but I haven't seen compelling evidence that those arguments in favor of a center bicycle track necessarily apply east of Pearl St.
Ari's blog post says that bicycle traffic calming in the vicinity of Pearl St is desirable. I'm wondering if having bicycles cross over between center and outside lanes at Pearl St with a traffic signal would be effective bicycle traffic calming. That light would presumably normally alternate between two phases, one to allow bicycles to proceed (and pedestrians to cross the automobile lanes) and the other to allow westbound automobiles to proceed along Mass Ave and to turn onto Pearl St (while pedestrians cross the bicycle lanes), and when a Boston bound bus is ready to go through the intersection, that could trigger a third phase to permit that movement.
Ari's blog post proposes that people wanting to catch the outbound 64 would not be able to catch it at the Mass Ave stop when it is extended to Kendall. If there's a center cycle track at Norfolk St in conjunction with a center of the road bus stop west of Pearl, that center cycle track would be in the way of rerouting 64 to take Norfolk St instead of Prospect from Broadway to Mass Ave; with outside bicycle lanes, the road would be straightforwardly compatible with that reroute to Norfolk St in one direction.
Ari writes about the center cycle track being an effective way to prevent right hook collisions. If we had outside bicycle lanes from Lafayette Sq to Pearl St and banned Boston bound automobiles on Mass Ave from Pleasant to Pearl, and kept one way streets as one ways in their current directions, the only place where automobiles could make right turns from Mass Ave between Lafayette Sq and Pearl St would be to Douglass St, and a dedicated right turn lane for automobiles like
this with a no right turn on red sign and a don't walk / red bicycle indication during green right arrow might work, although the parking lane on the Boston bound side there may be a bit too narrow and so some further refinement to that exact cross section is probably needed. (That automobile right turn lane would probably get a green only when a sensor would detect a vehicle present.)
For fire trucks, I think the center cycle track from Sidney to Pearl is undesirable if it forces them to commit early either to the left of cycle track bus lane which might give them priority unless they get stuck west of Pearl at the bus stops if buses are loading / unloading in both directions, or else commit to the right side of the cycle track and potentially get stuck in traffic; a design where they can freely move between the bus and general purpose lanes would probably be better for fire trucks.
West of Prospect, I think the argument for the center bicycle lane is mostly that the Mass Ave / Prospect light is at a busy intersection with lots of traffic proceeding along Prospect, and so it's desirable to make the west of Prospect configuration basically match the east of Prospect configuration so that everyone proceeding along Mass Ave at Prospect can share a single traffic signal phase and not conflict with each other. (Given the bus stop locations, I suspect that keeping the cyclists away from the Red Line headhouses west of Prospect may not be necessary, but minimizing the number of traffic light phases needed means there should probably be center bicycle lanes west of Prospect regardless.)
Keeping Harvard bound cyclists to the south of Harvard bound automobiles at Essex St and Temple St is probably the best way to prevent right hooks. (Temple St could also possibly be the outside to center bicycle lane crossover point, although I think Temple St as the crossover point probably doesn't reduce the number of phases the Pleasant St light would need vs having the crossover point at Pleasant St, and not needing a traffic signal at Temple St would be nice.)
I think protected outside bicycle lanes between Pleasant St and Inman St would probably be a better design that what Ari's blog post shows with the center bicycle lanes there.
After looking at Ari's visuals a lot and thinking about it a lot, I've found myself thinking that the Harvard bound center of the road bus stop doesn't seem ideal in terms of the Red Line to bus transfer path and the amount of waiting area that can be provided for bus passengers, and keeping the existing sidewalk bus stops and designing bus lanes to use them may be best.
I'm thinking that
east of Pearl St it might make sense to have outside bicycle lanes, and at the center of the road, have a parking / loading zone lane (which at the crosswalk would instead be an area for pedestrians to wait), a Harvard bound automobile lane, a lane shared between buses heading towards Prospect and automobiles turning left to Pearl, and then a lane for Boston bound buses.
Then
west of Pearl St, from north to south there'd be a parking / loading zone lane, an automobile lane, a bus lane, flex post space, the bidirectional cycle track, buffer space without flex posts, and the Boston bound bus lane.
Essex St would get a traffic signal that would stop the automobile lane when a bus is approaching, so that the bus could move over to the right lane through that intersection so that
west of Essex the order from north to south would be bus lane, automobile lane, left hand parking / loading zone lane, flex posts, center cycle track, buffer, Boston bound bus lane. (It would also be necessary to confirm that the bus could pull up to the curb after making that abrupt lane change.)
East of Prospect, Mass Ave narrows, so it probably would end up with just a right turn lane, a lane for automobiles and buses proceeding toward Harvard (which would also be used by buses turning left to Prospect), the bidirectional cycle track, and the Boston bound bus lane.
I think this would be more involved than the flex post protected pilot on Cambridge St between Inman Sq and Harvard Sq in that it would require some new traffic signals, but it might be possible to do this with just paint, flex posts, and traffic signal work.
(And the Boston bound buses would probably need to have the option to move into the center cycle track in this configuration if they need to get around a disabled bus, although if this is done I would like the drivers to be instructed that they are only allowed to do that at a walking speed if there is an actual broken bus, and if the bus in front of them is merely taking longer to load than their bus, they need to simply stay in the bus lane and wait for that bus in front of them to finish loading.)