INTRODUCTION
Northwood Ravin and Alberta Development Partners are proposing to redevelop both the Sears and Macy's within the Streets at SouthGlenn shopping center in Centennial. The proposed redevelopment includes additional retail, residential, office, and entertainment uses.
Felsburg Holt & Ullevig (FHU), a transportation consulting firm, has completed this Traffic Impact Study (TIS) on behalf of the developers to assess the effects of project-related vehicle trips on adjacent roadways and to identify roadway improvements needed to accommodate anticipated traffic. The study was based on development data provided by Northwood Ravin, Alberta Development Partners, the City of Centennial, and on local conditions documented in summer 2019 including while school was in session.
DEVELOPMENT SCENARIO STUDIED
This study assessed the anticipated impact of a maximum development scenario for the proposed application that consists of 1,071 additional residential dwelling units, including 148 units that are currently permitted by zoning but not yet built, and up to 280,000 square feet of new entertainment, office, and retail space. Maximum development scenarios are routinely studied in traffic studies to identify and prepare for the highest potential impact. Any future applications that exceed this scenario would require an additional traffic study.
TRAFFIC STUDY RESULTS
This study concludes that the proposed development's vehicle trips, along with existing and future regional traffic growth, can be accommodated while maintaining acceptable operating levels.
The traffic counts conducted for this study represent AM and PM peak hour conditions for a typical commuter day. The intersection counts were collected in 15-minute increments during the hours of 7 - 9 a.m. and 4 - 6 p.m. The counts along Easter Ave were taken on Wednesday, December 5, 2018. The remaining intersections were counted on Tuesday, July 30, 2019. Additionally, counts were gathered at University/Easter Pl and Race/Arapahoe Rd on Wednesday, August 21, 2019. These two additional counts were used to account for school traffic. Tuesday, Wednesday and Thursdays are used as a “typical” commuter day (this is when volumes will most likely be the greatest).
Even though the additional vehicle trips can be accommodated while maintaining acceptable levels of service, it is estimated the potential redevelopment at The Streets at SouthGlenn will generate additional peak hour trips along adjacent roadways. The following table shows the percentage increase in traffic volume for adjacent roadways during the morning and afternoon rush hours under the development scenario studied. Most adjacent roadways experience less than a 10% increase in traffic volume. These projections are conservative. Increase in volumes is likely to be fewer than projected.
WHAT IS DRIVING THE ADDITIONAL TRIPS?
The proposed redevelopment includes additional retail, residential, office, and entertainment uses. Each use generates a different amount of peak hour vehicle trips, with retail generating the most (56%).
LEVEL OF SERVICE (LOS) DEFINITION
Level of Service (LOS) at intersections measures how much delay a driver can anticipate. It is the key indicator used to determine needed traffic mitigation improvements. Levels run from “A” to “F” and describe the operation of the intersection during peak times. The City requires the nationally accepted best practice of LOS levels of D or better.
Key Point: For everyone to experience A or B levels of service on their commute, it would require funding to expand the streets by adding several lanes in all directions. That's a lot of taxpayer dollars!
LEVEL OF SERVICE PROJECTIONS
The following table shows the level of service at each of the 15 intersections at The Streets at SouthGlenn under five different scenarios:
- existing traffic,
- a short term projection with regional traffic growth factored in,
- a long term projection with regional traffic growth factored in,
- a short term projection that includes the proposed development at full build out and regional growth, and
- a long term projection that includes the proposed development at full build out and regional traffic growth.
MITIGATION MEASURES
Of the 15 intersections studied, two are identified as needing traffic mitigation improvements due to regional traffic growth independent of the proposed development project and because of existing traffic crash data.
S. UNIVERSITY BLVD / E. DAVIES AVE
The intersection of University and Davies is recommended to be converted to a right-in/right-out only intersection due to existing traffic crash and level of service data. Mitigation measures are recommended to be implemented in the short term future. The existing intersection can be seen in the photo above while an example of a right-in/right-out intersection can be seen below.
EXAMPLE OF RIGHT-IN/RIGHT-OUT (RIRO) INTERSECTIONS
RIRO intersections are designed to accommodate high volumes of traffic with low delay and high safety. Restructuring the traffic lane to only one direction increases safety through reducing the number of conflict points between vehicles.
ARAPAHOE RD / VINE ST
The intersection at Arapahoe Rd and Vine St is currently operating below City LOS standards. A traffic signal change called split phasing is proposed to mitigate this condition. Once the traffic signal change is in place, level of service is projected to improve compared to today – even with the regional traffic growth and trips generated by the proposed development included.
SPLIT PHASING SIGNAL TIMING
Split phasing would allow all northbound Vine St. movements (left, through, right) to occur at the same time. Once the northbound phase is complete, northbound signal changes to red. Next, the southbound Vine St. movements (left, through, right) would get a green signal.
TRAFFIC ENTERING ADJACENT NEIGHBORHOODS
Additional vehicle trips entering adjacent residential neighborhoods due to the proposed development is limited (10 or less trips per intersection during a peak hour).
The following diagram shows the projected number of peak hour vehicle trips leaving SouthGlenn and entering nearby neighborhoods in 2022 with only regional traffic growth and compared it to the proposed development and regional traffic growth factored in.
PLEASE NOTE:
This traffic study was conducted by professional traffic engineers (Felsburg Holt & Ullevig) that utilized on the ground traffic counts, the Trip Generation Manual by the Institute of Transportation Engineers, sophisticated models, among other tools to study traffic impacts. The Trip Generation Manual is based on data gathered nationally over many years.
NEIGHBORHOOD TRAFFIC MANAGEMENT PROGRAM (NTMP)
Are you concerned about speeding or cut-thru traffic in your neighborhood? The City wants to keep neighborhoods safe for pedestrians. Centennial has a comprehensive Neighborhood Traffic Management Program (NTMP). The intent is to create solutions for responding to neighborhood traffic mitigation requests.