18th Avenue and 89th Street Intersection Control Study

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Consultation has concluded

This study is complete and recommendations have been implemented.

Background:

The local street intersection of 18th Avenue S and E 89th Street has been monitored for several years for safety based on resident concerns. This area is anticipated to be a part of the 2022 Pavement Management Program. This provides the opportunity to proactively address the intersection safety concern with a built solution that could be constructed as part of the PMP work in 2022. A device trial study was completed in Fall 2021 to determine a recommended treatment for the intersection to be installed with the 2023 construction.


Public Open House:

As part of the proactive traffic calming process for local roadways, Engineering hosted a neighborhood meeting in this area to work with the residents to identify all of the traffic safety issues and propose options to address the safety concerns. The Public Open House was hosted on Tuesday, September 14, 2021 at Cedarcrest Park between 4 and 6 p.m. Residents were invited (by direct mailing to approximately 200 addresses) to stop by between 4 and 6 pm to share with staff their observations and issues related to mobility and safety at this intersection. The City provided traffic data and treatment options being considered. The open house was attended by 10 residents.


Temporary Device Trial #1 - Curb Bump-outs and 2-way Stop Control

The first temporary device trial was installed the week of September 27, 2021, with traffic data collection happening before installation and while the device had been in place for a while.


Temporary Device Trial #2 - Traffic Circle Intersection Control

The second temporary device trial, a traffic circle, was installed November 1, 2021. While this device was in place, mobility through the intersection was confirmed with a school bus, snow plow, and fire vehicles.


Results and Recommendations:

The data collection efforts before and during the first temporary device trial showed little to no impact on speeds (slight increase in north-south average traffic speeds) with the curb bump outs and stop signs. It was determined that with the wide roadway, there was not enough vehicle deflection imposed on the drivers with the curb bump outs to have a significant impact on the vehicle speeds north-south through the intersection. There were positives observed with this design in that the bump outs ensured that the stop signs were open and apparent to the drivers (not obstructed by vegetation or parked vehicles).

The data collection efforts for the second temporary device trial showed a reduction in vehicle speeds through the intersection and self enforcing intersection control and crash reduction or elimination based on the geometric changes. The traffic circle would result in an increase in the amount of time that it takes for snow removal in the area.

Based on the results of the two device trials, staff recommended that the next step for crash mitigation for the intersection be to install stop control on the east and west approaches to the intersection. The curb bumps outs were not recommended for installation with the 2022 PMP overlay project dues to their limited impact on speeds relative to the construction cost for installation. The full traffic circle would address the safety concerns but will not be recommended as a first step in mitigation given the construction cost and maintenance impacts. The intersection will be monitored and if the crash problem persists or if vehicle speeds on 18th Avenue create a new safety concern with the stop signs in place, a future step for mitigation would likely be to recommend construction of a traffic circle.


Next Steps:

As a part of the 2022 PMP Overlay project that will take place in the summer/fall of 2022, stop signs will be installed on the east and west approaches to the intersection (on both of the legs of E 89th Street). Following this intersection control addition, the intersection will continue to be monitored for both crashes and speeds to determine the impacts of the intersection control and determine if any additional mitigation steps are needed.

This study is complete and recommendations have been implemented.

Background:

The local street intersection of 18th Avenue S and E 89th Street has been monitored for several years for safety based on resident concerns. This area is anticipated to be a part of the 2022 Pavement Management Program. This provides the opportunity to proactively address the intersection safety concern with a built solution that could be constructed as part of the PMP work in 2022. A device trial study was completed in Fall 2021 to determine a recommended treatment for the intersection to be installed with the 2023 construction.


Public Open House:

As part of the proactive traffic calming process for local roadways, Engineering hosted a neighborhood meeting in this area to work with the residents to identify all of the traffic safety issues and propose options to address the safety concerns. The Public Open House was hosted on Tuesday, September 14, 2021 at Cedarcrest Park between 4 and 6 p.m. Residents were invited (by direct mailing to approximately 200 addresses) to stop by between 4 and 6 pm to share with staff their observations and issues related to mobility and safety at this intersection. The City provided traffic data and treatment options being considered. The open house was attended by 10 residents.


Temporary Device Trial #1 - Curb Bump-outs and 2-way Stop Control

The first temporary device trial was installed the week of September 27, 2021, with traffic data collection happening before installation and while the device had been in place for a while.


Temporary Device Trial #2 - Traffic Circle Intersection Control

The second temporary device trial, a traffic circle, was installed November 1, 2021. While this device was in place, mobility through the intersection was confirmed with a school bus, snow plow, and fire vehicles.


Results and Recommendations:

The data collection efforts before and during the first temporary device trial showed little to no impact on speeds (slight increase in north-south average traffic speeds) with the curb bump outs and stop signs. It was determined that with the wide roadway, there was not enough vehicle deflection imposed on the drivers with the curb bump outs to have a significant impact on the vehicle speeds north-south through the intersection. There were positives observed with this design in that the bump outs ensured that the stop signs were open and apparent to the drivers (not obstructed by vegetation or parked vehicles).

The data collection efforts for the second temporary device trial showed a reduction in vehicle speeds through the intersection and self enforcing intersection control and crash reduction or elimination based on the geometric changes. The traffic circle would result in an increase in the amount of time that it takes for snow removal in the area.

Based on the results of the two device trials, staff recommended that the next step for crash mitigation for the intersection be to install stop control on the east and west approaches to the intersection. The curb bumps outs were not recommended for installation with the 2022 PMP overlay project dues to their limited impact on speeds relative to the construction cost for installation. The full traffic circle would address the safety concerns but will not be recommended as a first step in mitigation given the construction cost and maintenance impacts. The intersection will be monitored and if the crash problem persists or if vehicle speeds on 18th Avenue create a new safety concern with the stop signs in place, a future step for mitigation would likely be to recommend construction of a traffic circle.


Next Steps:

As a part of the 2022 PMP Overlay project that will take place in the summer/fall of 2022, stop signs will be installed on the east and west approaches to the intersection (on both of the legs of E 89th Street). Following this intersection control addition, the intersection will continue to be monitored for both crashes and speeds to determine the impacts of the intersection control and determine if any additional mitigation steps are needed.