Transportation for Life

Comments on DCR’s Proposed Arborway Improvements

Overall, the DCR’s proposed ideas for long-term improvements for Arborway, from Kelly Circle (at Jamaica Pond), through Murray Circle, to Forest Hills, are fantastic. Still, there are a lot of details that need attention, and some of the alternatives presented are not acceptable. So, here are my comments.

At Murray Circle (Arborway = N-S street, Centre = E-W street)

1. Both roundabout alternatives at Murray Circle are unsafe / unacceptable. This is because they involve unsignalized multilane exits, which are inherently unsafe to pedestrians and cyclists due to multiple threat (a car may stop in one lane, but not the other). Multiple threat is particularly bad at roundabout exits, where it’s impossible to predict until the last moment whether a circulating car is going to exit or not. Those crossings cannot be made safe with an RRFB (because RRFBs don’t effectively stop traffic, so a car in one lane may stop while a car in the other lane plows through) or with a HAWK beacon (which makes crossing safe for those who cross at the start of the HAWK cycle, but not for those who arrive late in the Walk interval or during the Flashing Don’t Walk interval, when cars have a flashing red and cars in one lane may remain stopped while cars in the other lanes go).

2. At Murray Circle, for the Centre/JP approach, it is clearly better to have a simple right turn lane (Alternative 4) than to have a slip lane for that movement (Alternative 3). However, this assumes that the “simple right turn lane” alternative will include a traffic signal for the right turn movement, with either all or most right turns running with the southbound left turn from Arborway onto Centre/JP, and few or no right turns running concurrently with the bike-ped crossing adjacent to the right turn lane. The right turn volume there (more than 250/h in the am peak) is too great to allow a typical concurrent crossing with a permitted right turn conflict.

3. At a signalized Murray intersection, crosswalks on three of the legs (all except across Centre St – JP) must run without right turn conflicts because of high right turn volumes. That will require adding a right turn lane on the Centre St (Faulkner) approach. That right turn can run at the same time as NBL; it is also possible to split the EBT phase so that part of it is concurrent with a parallel crossing, and the rest serves EBR (with EBR overlapping the full NBL phase and part of EBR).

4. At Murray Circle, for the slip lane from Arborway southbound onto Centre/Faulkner, the pedestrian crossing of that slip must be signalized with a very short cycle.

  • The crossing must be signalized because nothing other than a red light will stop the very heavy traffic in this slip lane. Because the pedestrian clearance time will be very short, a HAWK beacon would impede traffic just as much as a regular traffic signal, and be less effective at stopping cars.
  • The crossing must have a very short cycle because it is one stage in a two-stage crossing. Because the other stage is across Centre Street for some people and across Arborway for others, it is impossible to coordinate the two stages, and so the only way to avoid intolerably long delays at such a 2-stage crossing is for the slip lane’s signal cycle to be very short, so that nobody waits long to cross it. The pedestrian phase will need only 12 seconds (7 s for Walk, 2 s for Flashing Don’t Walk, and a 3 s pedestrian phase end buffer). Cars will have enough capacity if the cycle length is 30 or 35 s in the pm peak and 25 s at other times. The signal governing this crossing can operate independently of the signals at the main intersection; there is no need to coordinate them.
    • This precaution was not heeded in the Casey Arborway project, and as a result, where Arborway meets South Street, is that average pedestrian delay is 241 s crossing Arborway and 108 s crossing South Street (here’s the study that shows that). A generally accepted limit for tolerable average delay is 40 s.
  • The pedestrian phase for crossing the slip lane should be on recall because during hours of peak bike/ped use that lowers pedestrian / bike delay, and at other times it helps to slow down traffic. With a cycle length of 25 s (35 s in the p.m. peak), delay to autos will be short.

5. For the southbound approach to Murray Circle on Arborway, having two thru lanes (as in Alternative 4) is the only realistic solution given the high through volume in the pm peak; however, the approach geometry has to be revised so that both through lanes will actually be used as full lanes. In the current configuration, hardly any cars will use one of the lanes (and if they do, they’ll block the entrance to the right turn slip lane). In the plan my students made in 2008, we recognized this bottleneck, and allowed thru traffic from Parkman and Pond Street to use the SB carriage road to get to Center/Faulkner. All of the alternatives shown force carriage road traffic onto the main barrel in advance of the Murray intersection, which is commendable, but doing so may require adding a long right turn lane (a 5th lane) to the main barrel, with significant impacts on trees.

Main Barrel

6. The “shared street” alternative (Alternative 3) is unacceptable because the road configuration won’t keep all traffic except local from using the carriage roads. For example, traffic from Centre/JP will be tempted to skip the light at Arborway and use Prince / NB Carriage Road; and traffic from Parkman and Pond will be tempted to skip lights by using the SB carriage road. Cyclists dislike block paving. Cyclists need to be able travel both ways, and it isn’t clear that a shared street would allow contraflow travel. The transitions from where bikes are in a path to where they enter the street will be stressful because they require cyclists to look behind them (over the shoulder) for conflicting traffic. The only way a shared street alternative would work is if the traffic direction on the carriage roads is reversed from what it is today, with cars reversing direction to enter and exit the carriage road; that would keep all but immediate local traffic on the carriage roads.

7. Between Murray Circle and Eliot Street, a safe bicycling provision – a cycle track or shared use path – should be provided on both sides of Arborway. While this provision is currently part of only one of the alternatives, it can be added to the other alternatives.

  • West side (Pond side): This side will be the main through route for cycling, considering paths that continue to the north and to the south. To limit conflicts with pedestrians, the west side should have a bikes-only path. For pedestrians on this side, there will be a sidewalk; there could also be a footpath in the median, perhaps with a surface that is pervious to rain.
  • East side (city side): This side is vital for cycling between the Arborway Hillside neighborhood (Jamaica Street, little Arborway, etc.) and to JP Center; without it, people would have to cross Arborway twice, or use South Street, which has no bike lanes. It is also valuable for abutters on Arborway, who otherwise would have to ride on the sidewalk. Because of lower bike demand on this side, the provision on this side could be a shared use path.

8. The main barrel must have pedestrian crossings with reasonably close spacing. The first crossing south of Eliot must be no further than at Pond Street. In any alternative with greater spacing, a crosswalk at Pond can and should be added. Skipping a ped crossing at Prince Street is OK as long as there’s one at Pond.

9. Providing extra pavement on the carriage roads just for fire engines is a waste that should be avoided. Providing an asphalt-paved shoulder that isn’t meant for parking so that cars can pull into it when a fire engine wants to pass violates principles of minimizing pervious surface and traffic calming. Fire engines need to use the carriage road only for access to the small number of abutting homes (thus, very infrequent fire trucks); the carriage road will have little traffic; and it isn’t moving cars that block fire trucks, but stopped cars. The general solution to fire access is to avoid the need for cars and delivery vehicles to stop in the carriage road. This can be accomplished by providing occasional pullouts for a vehicle to pull into the tree lawn either between driveways (as they often do now) or by pulling onto a driveway that has broadened in the tree lawn area to create pullouts that can be used momentarily, but not for parking. Pullouts can be paved with grasscrete – that is, a concrete mesh with holes through which grass grows.

Kelly Circle

10. In Kelly Circle’s Alternative 4, the mini-roundabout is unsafe for bikes. What’s more, the bike-ped crossing at that mini-roundabout will interfere unacceptably with the nearby traffic signal. Plans show an unsignalized crossing across 3 lanes with heavy traffic volumes. That is unsafe and will be full of high-stress interactions all day long. That ped-bike crossing will also bring traffic to a standstill in the middle of the Arborway/Prince intersection whenever peds or bike cross while the northbound left turn phase is running. Traffic flow at that signalized intersection can only work well if pedestrians and bicyclists stop while that left turn is running – which demands a signal, as provided in the otherwise almost-identical Alternative 2.

11. Kelly Circle’s Alternative 1 (retaining the large circle) has an unrealistic lane reduction, and a stressful bike/ped crossing at the rotary exit onto Parkman.

  • Alternative A reduces the rotary to two lanes where the J-way enters, with the right lane forced to exit onto Parkman. That seems unrealistic, because nearly nobody from J-way is headed to Parkman Drive. There will be huge backups. If drivers on the J-way complied with lane restrictions, the J-way’s right lane would be nearly unused while the left lane would be backed up for a long distance, which is both unsafe and unsustainable. At the same time, a dedicated exit lane for Parkman Drive, as exists today and as proposed in Alternative A, remains essential for a safe crossing, so three lanes will be needed from J-Way to Parkman Drive.
  • Many cyclists report routine close calls at the rotary exit onto Parkman. It will be a challenge to make this crossing safe and low-stress. A bigger jughandle for the path would make it so that southbound bikes and cars exiting the rotary approach more at right angles to each other. A raised crossing at the crosswalks with a sharp, high ramp that really slows cars to 10 mph would help.

12. Kelly Circle’s Alternatives 3, with double intersections at Pond, is a promising idea, but it will need a much longer left turn lane. Consider adjustment to the connector road geometry and ped crossing, too. The proposed geometry makes travel from the Carriage Road southbound to A-way southbound tortuous, and likewise for A-way northbound to Carriage Rd northbound; however, these are heavy flow movements that should be facilitated. Consider reorienting the cross-road to facilitate those movements. Regarding a ped crossing of the main barrel, I imagine the phasing plan will be 1) NBL & NBT, 2) SBT, NBT, and bike path, 3) SBR, Pond, and possibly ped crossing across the south-side leg with permitted right turn conflict, and 4) Carriage Road, possibly with a ped crossing with permitted left turn conflict across the north-side leg of the main barrel. If you reorient the connector road, running peds during phase 4 looks promising, since few cars make the conflicting movement (reversing direction from Carriage Rd SB to A-way NB) and the geometry will force that turn to be slow.

13. Alternative 2 can be improved by realigning its main barrel intersection with Prince Street, adding a shared use path on the city side, and making the crossing at Pond Street more direct.

  • By realigning the main barrel intersection at Arborway with Prince Street (JP Center side), local access issues that plagued Alternative 2 can be resolved without the need of a mini-roundabout. With that realignment, drivers aiming for Prince St (JP Center-side) would be able to reach it from Parkman or Pond Street via the realigned intersection, and from J-way southbound, by going around Jamaica Pond using Perkins / Parkman.
  • While Alternative 2 has a shared use path on the city-side from Prince Street north, it lacks one in the main barrel; that could, and should, be added.
  • The pedestrian crossing (across the main barrel) at Pond Street should be more direct, not forcing pedestrians to walk 100 ft parallel to Arborway. At the same time, eliminating the pedestrian crossing at Prince Street (as in Alternative 4) seems necessary and inevitable, because turning flows there will be too large for a safe concurrent crossing. That should be acceptable as long as the Pond St crossing remains.
  • It is not obvious to me which is better, double intersections at Pond (used in Alternative 3) or at Parkman (Alternative 2). Both are worth exploring further.

From Murray Circle to Forest Hills

14. Upper Arborway needs advisory bike lanes, with centerline removal. This street, which is essentially Arborway’ service road along Arborway Hillside from Forest Hills to Murray Circle, is a bike route, and bikes in mixed traffic on a road with a double yellow centerline (the current condition) is high-stress when the traffic volume exceeds 1,500 per day, while with advisory lanes it can be low stress for volumes up to 3,000 or 4,000. For examples of advisory lanes, see advisorybikelanes.com.

15. Retaining parking for Arborway visitors seems like a no-brainer; a shared use path there will limit impervious surface. The parking there is well used on nice weekends, and retaining it fits with the DCR’s mission of promoting enjoyment of parks. Where the only pedestrian demand is people walking to/from their cars, providing a shared use path rather than separate bike / ped paths seems reasonable.

16. At Centre / Prince / Little Arborway, to facilitate pedestrians crossing Centre between little Arborway and Prince, add a crossing island in the middle of Centre Street’s east-side leg. That will work better than a raised intersection, and unlike a raised intersection, will not interfere with traffic flow/capacity at the Murray traffic signal. A crossing island there will make it hard for large vehicles to turn right from little Arborway onto Centre; that can be remedied by making the island so that large vehicles can overrun it, e.g., by using a 3-inch curb reveal.

At Forest Hills

17. Some of the traffic signals at Forest Hills force bikes and pedestrians to cross in multiple stages; they give atrociously bad service to pedestrians and bikes and need to be retimed. Average delay for one pedestrian crossing is more than 4 minutes! The signals need to be retimed so that pedestrians get good coordination from one stage to the next. I’ve written about this elsewhere.