Traffic Calming Study Report
Prepared during November, 2014 by Bob Edmiston
This study was conducted by Madison Park Community Council (MPCC) with traffic count data and barricades graciously provided by the Seattle Department of Transportation (SDOT) at no cost to the community. The study request to MPCC was initiated by Denny Blaine Neighbors for Safer Streets (DBNFSS).
This study examined the effectiveness of a recommended solution from a previous traffic study, commissioned in April, 2000 (Transpo 2001). The present study had several key findings:
Recommendation: While it may be possible to simplify the E Harrison St @ Lake Washington Blvd @ 37th Ave E intersection to make it intuitive and safe for all transportation modalities, the observational data from this study do not support a recommendation to permanently implement the experimental intervention without also addressing the usability issues found in the observational and survey data.
The Denny Blaine neighborhood is located in Seattle, WA and is bounded by the Madison Park and Washington Park neighborhoods on the north, Lake Washington on the east, Madrona neighborhood on the south, and Madison Valley on the west. The neighborhood primarily consists of single-family homes, with neighborhood schools and parks.
Figure 1. Historic Dorffel Drive in the Denny Blaine Neighborhood Context.
High traffic volumes and speeds have historically been a concern of Denny Blaine residents. Commuters and parents driving children to nearby schools heavily use local streets as cut-through routes. As a result, vehicles regularly use the residential streets in lieu of the designated arterials to travel in the north/ south direction through the neighborhood. Residents on the impacted narrow residential have long been concerned with the volume of traffic as well as the speed at which motor vehicles travel on their residential streets. (Transpo 2001 study)
Figure 2. Denny Blaine Arterial Street Network with Historic Dorffel Drive in Green
As of the last comprehensive professional traffic study, conducted by The Transpo Group Inc in 2000 (Transpo2001), motor vehicle volumes on Dorffel Drive exceeded 3,000 motor vehicles per day during weekdays. At that time, motor vehicle volumes were over twice the recommended limit (1,500 TDV) for a modern residential street, and six times what is recommended for a walking and biking route for children to get to school (500 TDV). Since Dorffel Drive is a narrower than standard (18 vs 25 ft pavement width) historic drive, the adverse impact caused by excessive traffic volumes and speeds on livability for residents who live and walk on Dorffel Drive is felt disproportionately.
The primary recommendation of the Transpo2001 study was to “Reconfigure 37th Avenue E @ Harrison Street @ Lake Washington Boulevard intersection.” Further explaining: “The intersection today invites southbound traffic on Lake Washington Boulevard to use 37th Avenue E, rather than continuing south on Lake Washington Boulevard. This option would reconstruct the southeast corner to create two separate intersections from the existing one large intersection. The intent behind this project is to discourage use of 37th Avenue E over Lake Washington Boulevard, and as a result reducing through traffic volumes on 37th Avenue E without prohibiting access for local traffic.”
The objective of this 2014 study was to empirically investigate the effectiveness of the least intrusive of the intersection redesign recommendations from the Transpo2001 study.
The current study evaluated this primary recommendation from the Transpo2001 study: “Upon proven success of a trial period, the neighborhood could construct the measures as permanent features.” On a 2014 site evaluation with representatives from the Seattle Department of Transportation (SDOT), a traffic engineer agreed that prior to committing to a particular permanent change, prudence warranted conducting a six week trial period. During this trial, both quantitative and qualitative data were collected in addition to soliciting qualitative feedback from the surrounding community.
The participants in this study were the people who already drive, walk or bike on Dorffel Drive. Since this was only a temporary intervention, a decision by SDOT was made to not send out notifications or conduct an involved public process. Such notifications are costly and warranted only when permanent major reconfigurations, or changes of roadway functions, are being proposed. This study did not meet the warrant for postcard notification. However, word was spread about the upcoming study electronically using social media, web sites, phone calls and neighbor to neighbor communication. Since there is no one way to reach all who use Dorffel Drive, many people were surprised by the overnight reconfiguration of the intersection.
The materials for the study consisted of
Figure 3. Orange Lines Indicate Barrier Placements.
Figure 4, Barricades In Place (after two in the distance had been stolen by vandals)
Figure 5. Seattle Department of Transportation automated traffic speed and volume counter.
Figure 6, Measured risk on 37th Ave E for people walking or biking as a function of motor vehicle driver behavior for the April 2014 baseline and the October 2014 trail conditions.
Figure 7, Effect of vehicle speed on pedestrian lethality (source: National Highway Traffic Safety Administration Literature Review on Vehicle Travel Speeds and Pedestrian Injuries, 1999) .
A long history of international transportation and public health research has established a direct relationship between the likelihood of survival of a pedestrian when they are hit by a motor vehicle and the speed of the vehicle. The lethality of the collision increases exponentially with the speed of the vehicle. In addition, the odds of a pedestrian getting hit by a car increases linearly with the number of opportunities to get hit. Both vehicular speed and vehicular volume are considered together when evaluating the relative safety of a roadway for people walking. In order to illustrate the combined influence of the linear effect of volume and the exponential effect of speed on lethality, a the log of traffic volume was used in Figure 6 above.
We hope that this innovative way of looking at traffic study data will hopefully give us a new instrument to re-examine publicly available, existing traffic study data, as well as a way to interpret future traffic study data from the perspective of the person walking.
The April baseline traffic study showed that
Driver speeding behavior was dramatically reduced during the October trial condition.
Top end speeding behavior (over 10 mph beyond the 25mph speed limit) dropped from 262 instances per week to one.
The April 2014 baseline automated traffic data from this study illustrated that the safety of 37th Ave E was severely compromised by both a high volume of illegal speeding behavior and by a surprisingly large amount of top-end speeding behavior (more than 10 mph over speed limit). The reason that top-end speeding behavior is worthy of study as a primary metric of safety is because a pedestrian hit by a top-end speeding driver (35+ mph in our context ) has an almost certain likelihood of being killed. The experimental intervention nearly completely eliminated the most lethal type of speeding behavior exhibited by drivers on 37th Ave E.
Figure 8, Total weekday traffic volume on 37th Ave E, just south of E Harrison St.
A total of 15,389 vehicles were counted on 37th Ave E over the seven day period between Sept 30, 2014 and Oct 6, 2014. During the October trial, the automated counter data showed 2,403 TDV (total daily volume) for motor vehicles on weekdays and 1,690 TDV average on weekend days.
The April 2014 count data is not directly comparable with the October 2014 count data because The Bush School was on spring break during the week that the April data was collected, but in full session when the October data was collected. Past research has shown that approximately 1/3 of neighborhood motor vehicle traffic consists of parents driving children to and from schools and afterschool activities. The April data showed 2,045 TDV for motor vehicles on weekdays, almost 400 cars per day less than during the trial, while The Bush School was in session. A total of 12,698 vehicles were counted over a seven day between April 1, 2014 and April 7, 2014, 2,691 less than during the intervention. However, the October data showed a 600 car per day reduction from the Transpo2001 study. Given that the Transpo2001 study was conducted 14 years prior, overall transportation behavior may be an alternative explanation for the reduction. Given the uncontrolled variables of school being in session and a 14 year lag since the Transpo study, comparing these three sets of numbers is methodologically problematic.
Extrapolated manual count data, collected by volunteers, showed that 285 people per day rode bicycles and 348 people walked through the E Harrison St @ 37th Ave E intersection on a daily basis. Most of the people observed walking school children and parents while most of the people riding bicycles appeared to be either commuting or exercising. Observations of children riding bicycles to school through this intersection were rare.
Four video measurements were taken: AM commute, AM school rush, Midday traffic and PM school rush. All of the video was manually logged and usability issues were identified through standard observational techniques.
The primary finding from the video analysis was that nearly all motor vehicle drivers negotiated the intersection slowly and carefully. However, not all went according to plan. The following usability issues obtained through review of the video recordings were confirmed by the comments obtained through the online survey data.
Figure 9. Confusion about which way to go around the E Harrison St median island.
Many southbound motor vehicle drivers from Lake Washington Blvd entering 37th Ave E experienced confusion regarding which route to take around the existing median island in E Harrison St at Lake Washington Blvd. During the course of the study, drivers were split between turning early and then making a quick left around the western terminus of the traffic island, and those taking the slower and more cautious route around the south side of the island before taking an immediate left. On occasion, cars were seen both directions at the same time. All of the observed drivers from either group negotiated the turn movement onto 37th Ave E at a very low rate of speed. The observed southbound ingress behavior to 37th Ave E was uniformly slow and courteous.
Figure 10. Tight squeeze as a result of two substandard turn radii in close proximity.
As a sub-issue of issue 1 above, some drivers who travelled around the eastern tip of the E Harrison St median island had difficulty staying in their lane due to the abnormally short turning radius. This problem was especially problematic for vehicles with long wheelbases. This put them in potential conflict with Northbound drivers exiting 37th Ave E who were forced to turn right around the tree, also with effectively zero turn radius. The close proximity of these two turning movements with substandard turn radii put traffic moving in opposing directions in close proximity. Since the speeds of both vehicles was very low in all cases, there was negligible risk for human safety, but property safety was a legitimate concern with this configuration. This close proximity of turning vehicles may have caused perceived danger in the minds of drivers, and therefore caused them to voluntarily choose to drive slowly and carefully through the intersection.
Figure 11. Low stop compliance locations.
With the new configuration, the two stop signs in the same traffic island combined to be ineffective. A large portion of drivers rolled through both stop signs. With the experimental configuration closing the in/out on the east side of the 37th Ave E median island, there was no legitimate reason to stop at the stop sign at it's current location. It was too far from Lake Washington Blvd to be effective. At a minimum, the stop sign location needs moving it’s current location in the traffic island to the corner with Lake Washington Blvd. Any redesign of this intersection will need to reconcile the location of the two stop signs.
Figure 12. Poor pedestrian accommodations and excessive unprotected crossing distances. Red: 135 foot exposed crossing distance. Orange: place where most pedestrians were observed crossing E Harrison St. Purple: path pedestrians were seen crossing the mouth of 37th Ave E during the intervention. Green: path students and parents took to cross Lake Washington Blvd.
Pedestrians along the western side of Lake Washington Blvd currently are exposed to 135 linear feet of walking in the roadway while exposed to fast moving traffic with numerous unpredictable turn movements. Therefore, it was not surprising to see that no pedestrians were observed walking directly from the NW corner of the intersection to the SE corner along Lake Washington Blvd. The few pedestrians and students that were observed riding bicycles had difficulty with the configuration. They all chose unmarked crossing points where the crossing distances were shorter and where they had to face fewer turn movements.
The large turn radius of the SE corner of the intersection of 37th Ave E at E Harrison St, enabled cars to turn onto southbound 37th Ave E from eastbound E Harrison St without having to slow down. Most pedestrians who crossed to LakeView Park showed signs of anxiety while crossing at this blind corner, where cars had no reason to slow down for the turn. This pedestrian safety issue existed before, but with the addition of the volume of traffic which used to go on the other side of the island, the issue became more problematic.
Figure 13. Preschool students from two schools and physical education students from The Bush School depend on daily safe crossings of Dorffel Drive to Lake View Park. Photo taken during the study.
Figure 14. A few weeks after the study ended, a car lost control and crashed, destroying the very same pedestrian sign seen behind the preschool teacher in Figure 13. Without the traffic calming configuration in place, residents have reported that the livability of Dorffel Drive has been degrading back toward baseline conditions as cars resume their top-end speeding behavior.
After school, the entire Bush lower school cross country running team crossed the entrance of 37th Ave E to access LakeView Park where they conducted their running practice. Approximately 40 children and adults were observed crossing to the park at this location. Adults stood in the roadway to ensure safe passage of the children.
In addition, a large group of preschool age children were observed walking cross 37th Ave E earlier in the afternoon, closer to the location where the automated speed data was recorded. The SDOT documented excessive top end speeding behavior represents a clear and present danger to both of these vulnerable roadway user populations (who were not included in the manual pedestrian count due to the mid-day timing).
The automated traffic study and the video observations showed two different results, likely due to the fact that the automated data was recorded mid-block whereas the video data was collected at the eastern terminus of E Harrison St.
From the video observations, much westbound traffic turning from northbound Lake Washington Blvd onto E Harrison St was observed moving through the intersection at what was perceived as a high rate of speed, but was unlikely over 25mph. The fact that these cars were crossing the end of 37th Ave E at perhaps 25mph, while people were slowly exiting 37th Ave E, may have caused a feeling of discomfort for some drivers. Eastbound E Harrison St traffic was slowing to the stop sign and was not therefore seen as moving unusually quickly.
The E Harrison St automated October, 2014 traffic count showed a different pattern of data, likely due to it’s mid-route location two blocks further west on E Harrison St. On E Harrison St, a higher percentage of drivers sped than on Dorffel Drive, but with a lower maximum rate of speed.
Eastbound E Harrison Street drivers speed more often, go faster when they do speed, and contribute three times as many top end trip speed measurements than westbound drivers.
Figure 15. Words people used to describe the role that Dorffel Drive serves in the lives of the people who use it on a regular basis.
Of the 158 responses collected from respondents who lived as far away as Rainier Beach, there was an interaction between household location and how people felt about it. Survey feedback from those who live on Dorffel Drive was positive, with most residents saying they loved it. Feedback from those who do not live on Dorffel Drive was mostly negative with most people saying they hated it, but not saying why or what specifically caused their feelings. Survey feedback did correlate with the usability problems identified through analysis of the traffic video recordings. We have no way of knowing if one caused the other.
Figure 16. Words that people used to describe their experience with using Dorffel Drive during the experimental condition.
Figure 17. Evidence of omnipresent night time vandalism behavior that plagued the study.
The trial configuration was vandalized seven times during the study. The barricades were repeatedly disassembled and strewn down the hillside and sometimes simply moved out of the way. Eventually, two entire barricades and supports were completely stolen from the location and never found. Each time the trail was vandalized, volunteers from the Denny Blaine Neighbors for Safer Streets (DBNFSS) organization retrieved the various components and reset the configuration to the best of their abilities, usually before the AM traffic rush. After barricades had been stolen and vandalized to the point where blocking the easternmost entrance to 37th Ave E was no longer possible, SDOT crews replaced the missing barricades and components.
The vandals were never caught, nor did they ever come forward and claim responsibility for their actions. The observed acts of vandalism appear to be one of the ways that the outrage about the experimental intervention was expressed.
The key takeaways from the study are:
In terms of impacting driver behavior, the primary goal of this study was to see if the trial intervention would have a positive influence on driver behavior. By positive, we mean influencing drivers to drive at a rate of speed that is both appropriate for a narrow residential school route and respectful of the residents who live along Dorffel Drive. The experimental configuration was successful at achieving the goal of safe and appropriate driver behavior on Dorffel Drive.
While the overall number of cars measured curing the automated studies between the baseline and trial conditions were nearly identical (8,576 vs 8,224), the trial caused the number of drivers who chose to speed to fall from 1,040 to 67. We can infer that the change in the configuration led directly to the nearly complete elimination of all speeding behavior on Dorffel Drive. In fact, the number of northbound speeders alone dropped from 906 to 42. The highest recorded driver speed between the April and October counts dropped by half from 77.7mph to 38.8mph.
Residents who live along the route have said that they experienced less traffic, and the traffic that behaved more respectfully to those walking and to drivers going in opposite directions. The fact that all of the cars are now driving at reasonable speeds may have led to the subjective perception of less traffic, even if roughly the same number of cars actually drove on Dorffel Drive.
The historical concerns of traffic volumes and speeds were validated by the April 2014 traffic counts and speed study. The results of the speed study in particular confirm that traffic calming measures are warranted along 37th Ave E and Dorffel Drive and a reconfiguration of the intersection that was the subject of this trial could contribute significantly to achieving the livability goals of the residents of Denny Blaine who live on Dorffel Drive and all who use it for walking or biking.
These calming improvements are necessary if Dorffel Drive is to achieve it’s potential as a safe-route-to-school that can serve Epiphany School, The Bush School and McGilvra Elementary School.
The experimental configuration should not be made permanent without reconsidering the design of the entire intersection. The unique way that the streets come together result in numerous complex interactions and turn movements. The quantitative and qualitative research data collected during this study can now be used to inform an open community redesign process, if the Denny Blaine community and city choose to move forward with improving this intersection or coming up with a solution to speeding that is effective, yet tolerable, to the surrounding community.
Figure 18. Potential intersection simplification design created by an volunteer architect who is a long time resident of Denny Blaine.
Madison Park Community Council
TinyURL for this report: http://tinyurl.com/lwkjaww
Full URL for this report: https://docs.google.com/document/d/1LdPjQDviTOoDkYOs6GAMwuGuOhu4-M6E_DBRujjJbn0/pub