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Construction on Chandler Mill to pilot current and alternate plans can begin soon

Updated: Feb 21, 2023

Designers must demonstrate that speeders can be slowed for the route to be open to all cyclists, regardless of the plan.

As described in an earlier post, the current plan advanced by the Greenway team is at an impasse. On the one hand, property owners on 75% of the route continue to stand their ground because of concerns about the design. And the Kennett Township Board of Supervisors (KT-BoS) has ruled out seizing the land needed for the current plan, but may have to return grants if they do not start demonstrating progress to funders soon. On the other hand, the KT-BoS has so far refused to act on our alternate plan that offers potential solutions but that pivots on demonstrating strategies that can slow speeders. So what do you do?


It turns out that you can pilot key portions of the current and the alternate plans right now at virtually no additional cost regardless of which plan is ultimately chosen. By completing a pilot and surveying users, we can compare the current plan and our alternative before committing $5.5-6M in remaining construction costs on the former. Let’s break these options down.


Traffic speed is key to both plans

The multimodal grants received for the Greenway require that the design safely accommodates all cyclists and pedestrians, and this is typically accomplished by constructing a 10’ wide shared use path. Since there is only enough room for a 6-8’ wide path alongside Chandler Mill road, however, cyclists must share the road with cars. So the success of both plans ultimately depends on nudging traffic speed downwards.


Designers use Bicycle Level of Traffic Stress (LTS) guidelines to identify the kinds of roads that all cyclists can comfortably share with drivers. For a road like Chandler Mill, this requires (1) a maximum prevailing speed (e.g., the 85th percentile of drivers) under about 30 MPH, and (2) that there are no sections with limited sight distance (LSD) where the driver cannot see far enough around a curve or over a hill to stop safely for something in the roadway (for example, a car traveling at 35 mph needs about 205’ to stop safely).


In any case, it just makes sense to target speed. Speeding drivers were the number one concern of those currently walking and cycling on the roadway. Until the current plan demonstrates that it can address speed, it offers no meaningful improvements for cyclists despite the $7M total price tag. So right now, the current plan may leave Chandler Mill uncomfortable for all but 10% of cyclists. Given the scant protection offered by the 2’ planted buffer between the road and the sidepath under the current plan, we also believe that every user would be more comfortable if drivers - especially the fastest - could drive at least a bit slower. And we do not need many drivers to change their behavior - these high prevailing speeds might simply result from as few as 12 residents each completing one round trip each day driving 5 mph too fast.


The goal: Nudge speeders down by 5 mph.

The current and the alternate designs propose to calm traffic using similar techniques to address overall prevailing speed. The good news is that one of these - longer two-way one-lane Yield section - was already piloted successfully in November 2021, nudging prevailing speed down to 31 mph within the section. So the 300’ two-way one-lane section just south of Hillendale in the current plan offers traffic calming that can also become integrated into the alternate plan. Completing this section now makes sense: it can be built immediately because Kennett has already acquired the necessary easements (it is still waiting for some permits), and this is also the section of the roadway with the highest prevailing speeds.


So we recommend not only building this section right now, but also continuing the sidepath as described in the current plan for the remaining 700’ south on the land that Kennett controls. This will help users see whether the destruction of virtually every tree within 15-20 feet of the road required under the current plan is worth it. If this two-way one-lane yield section looks as good as the designers claim, this may be all that Kennett needs to convince the remaining landowners to cede the Right of Way (RoW) needed to complete the current plan. If not, then Kennett can avoid spending another $5.5-6M completing a path that many would find objectionable. Construction can begin as soon as permits are approved.


But Kennett does not need to even wait that long. It was also clear from the November 2021 pilot, however, that more would be needed: the two two-way one-lane Yield sections did not nudge speeders downwards along the rest of the roadway, because they sped back up in until the next section. And this is no surprise - it is generally understood that traffic calming measures often need to be placed about every 3-600’ to reliably decrease overall speeds.


That is why the current plan includes additional traffic calming measures - 6 sets of speed cushions, and 4 short “choker” sections where drivers take their turn, in addition to the two longer two-way one-lane yield sections (see below). The designers proposed to place these equidistant along the route between Hillendale and Round Hill Road - about 600’ apart. This means that a driver traveling at 30 mph would encounter speed cushions, a choker, or a two-way one-lane section every 13s during the 2m 30s it takes then to drive the 1.2 miles. As we describe next, the alternate plan also uses similar measures, but strategically places them to first address LSDs.

Addressing LSDs

The current and the alternate designs use different strategies to address the 3 LSD sections identified. The most recent version of the current plan proposes shaving embankments to improve sight distance on 2 of the 3 LSDs, and to construct a 600’ long 9' wide boardwalk to circumvent the 3rd LSD. The solutions included in the current plan are very expensive - we would expect the boardwalk itself could cost at least $6ooK.

As described in detail elsewhere, our alternate plan proposes to position speed cushions just as drivers enter the LSD from either direction (see figure to the right capturing the southern half of the route) The rationale is simple: speed cushions can be designed to reliably drop speed to 20 or 25 mph, and we expect that this would be sufficient to eliminate the LSDs (a car traveling at 25 mph only needs about 125’ to stop safely). This is potentially much more cost-effective than shaving embankments, and would significantly decrease the cost of a boardwalk because it could be narrowed from 6’ wide because it no longer need to accommodate cyclists.


It is also possible, however, that placement of speed cushions at the LSDs before and after each of the three LSDs may be sufficient to drop overall prevailing speed. A simple traffic study can confirm the impact. If not, engineers can begin to pilot other options between the LSDs (like short, one lane “chokers”). Regardless, typical drivers (who already average around 30 mph) would notice little difference in their total travel time, except that they would have to slow by about 5 mph around the LSDs.


Best of all, the effect of the strategy on speed at the LSDs and overall speed can be quickly assessed, at little additional cost. Speed cushions can be purchased that can be quickly installed and moved as needed, with the results verified with a simple traffic study. If needed, temporary “chokers” can be placed elsewhere along the route to verify that we can nudge speeds down further still. This allows users to begin to experience how the road feels when drivers are slowed.


If this strategy proves successful at addressing the LSDs AND prevailing speeds, the potential to save million of dollars and hundreds of trees using the alternate design becomes very real. Why? Because to make the roadway comfortable for remaining users on foot (or even those using a wheelchair), we just have to address super-elevations along some curves in the roadway... and much of this can be accomplished during the repaving already scheduled.


The opportunity to get feedback - especially from local users - is key

One advantage of this approach is that we already have a pool of users who can provide feedback - the 2-3 dozen who regularly walk or cycle on Chandler Mill, and others who regularly walk one of Kennett's many quiet roadways. These users are already familiar with the behavior of drivers on Kennett's roads, and would be well-placed to comment on any changes in driver's behavior potentially resulting from the pilot. And of course, we would be especially interested in the experience of those who might be interested in trying the roadway out for the first time - all they need to do to help their township make the right decision is to park at the bridge and take an hour long walk or 15-20 minute bike ride. Signs along Chandler Mill Road with a QR code linked to a short online survey are all that is needed!


We suspect that feedback from other groups will not only be unnecessary, it may not be that useful. For example, those who do not walk roads in Kennett have no point of comparison. And for those who do not regularly walk trails, any discomfort they report might simply be do to the effort required. Feedback from those walking or cycling on the route right now is likely all we really need.

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