SouthGlenn developers, Centennial traffic engineer respond to traffic concerns

Traffic study on effects of mall redevelopment plan in spotlight

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The proposal to redevelop The Streets at SouthGlenn came with a companion study on the impact the redevelopment would have on traffic at intersections around the outdoor mall — including on major streets such as Arapahoe Road and University Boulevard.

During public meetings in November and December about the now-approved redevelopment plan — which would replace the former Sears and Macy’s buildings with apartments and new businesses — several area residents raised complaints about how accurate they felt the traffic study was.

Perhaps the biggest concern among them: the idea that traffic related to the former Sears land at SouthGlenn was improperly processed, throwing off the estimate of how much traffic would be added by the redevelopment.

The proposed redevelopment as a whole is expected to generate about 6,100 new vehicle trips per day, according to the study.

The traffic study appears to reach that conclusion partly by subtracting roughly 3,100 daily vehicle trips based on the idea that the redevelopment will remove the existing Sears building, according to page 27 of the study.

But because Sears closed near the end of 2018, the traffic study’s counts of existing traffic — which were used to help estimate what future traffic after the redevelopment would look like — appear to have partly, if not mostly, already accounted for the loss of Sears-driven traffic at SouthGlenn.

The number of vehicle trips that the traffic study assumes would be removed by the demolishing of Sears was estimated using traffic generation rates from the Trip Generation Manual from the Institute of Transportation Engineers from 2017. That’s a manual that provides standard estimates of car trips based on a destination business’ square footage. Using rates from that manual, the traffic study also estimates that the new development on the Sears land would add roughly 6,700 daily trips. 

In other words, the traffic study assumes that demolishing the vacant Sears would remove nearly half as much traffic as the upcoming new residential and retail buildings could add — 3,100 trips removed compared to 6,700 trips added. 

The Centennial Citizen asked officials with the redevelopment project — from Alberta Development Partners, Northwood Investors, and engineering firm Felsburg, Holt and Ullevig, which wrote the traffic study — why the study assumed that the demolishing of the vacant Sears would reduce traffic by such a large number.

In a statement, the group responded: “A number of the traffic data collection efforts were conducted when the Sears building was hosting a retail tenant. Since the most conservative numbers from the multiple traffic counts taken were used in our analysis, the baseline data does not assume that the building is empty.”

Sears traffic impact unclear

Traffic counts along Easter Avenue were taken in December 2018 for an earlier evaluation of the Sears redevelopment plan, according to the study. Those 2018 counts included the intersections at York Street (the “Mall Driveway”), Gaylord Street and Vine Street.

Upon the inclusion of the plan for redevelopment of Macy’s within the project’s scope, counts were taken at the remaining intersections along Race Street, Arapahoe Road and University Boulevard. The second set of counts was completed in July 2019. Two supplemental counts were conducted once schools opened in August 2019. Additional “AM peak hour” counts were taken in February 2020, the study says.

The Citizen asked the group whether the December 2018 traffic counts along Easter Avenue were taken before the Sears permanently closed. The Citizen also asked whether the August 2019 traffic counts occurred when Spirit Halloween, or another Halloween-themed retailer, was doing business in the former Sears space. The group did not respond to those questions by press time Dec. 14.

According to Anna Bunce, the City of Centennial’s traffic engineer, analyzing the traffic study isn’t as simple as looking at when the Sears had closed. Traffic calculations follow a certain methodology, according to the city.

Since a change in land use — generally changing from retail to residential — is what was proposed, the original possible use has to be shown as a subtraction, or reduction, and the proposed use has to be shown as an addition, or increase, Bunce said.

“The net (increase) is the result of what the reference standard manual indicates could be anticipated, as a standard projection,” Bunce said.

Other than the “unit quantity” — which appeared to mean amount of space at the property — and other than the fact that the study reflects a change in land use, “nothing about these (data) tables is site specific or meant to represent the actual condition” at SouthGlenn, Bunce added.

The developers’ team didn’t identify when exactly Sears closed. However, it would be unclear how much Sears traffic would have contributed to the traffic counts even if the data had been collected before Sears closed, Bunce said.

“If actual … turning-movement count data collection had been conducted prior to the Sears closing, it is unclear as to how much the Sears would have been actively contributing to the background (existing traffic) condition within what timeframe prior to the store closing, given Sears’ financial picture for some time leading up to the closure,” Bunce said.

She added: “It is also unclear what contribution the Macy’s — or any other specific single use internal to the site — is actually making to any of that data.” 

In terms of percentage increases in new traffic, the study says effects of the redevelopment would be mostly small.

Along Arapahoe Road, Race Street, University Boulevard and Easter Avenue — which form SouthGlenn’s perimeter — most of the changes in traffic volume caused by the redevelopment in the morning and afternoon would be less than a 10% increase and “do not represent significant changes to traffic flow,” according to the study.

But traffic changes along Race Street would be “significant,” the study notes. The increase would range from 37% to 49% depending on the time of day and whether looking at short- or long-term effects.

“This reflects the fact that Race Street has the lowest levels of background (existing) traffic of the surrounding roadways, so volume changes are more pronounced,” the study says.

Another measurement, the “level of service” — a qualitative rating of how well intersections function — is also given in the traffic study. Levels of service include A, B, C, D, E and F. Level A represents generally free-flow traffic and minimal delays, and level F indicates congestion and long delays, according to a city presentation.

“We prefer to arrive at a level of service C, but D is acceptable,” Bunce said during a city Planning and Zoning Commission meeting on Nov. 9 that discussed the redevelopment plan.

Acceptable levels of service can be maintained at the area’s intersections in accordance with current City of Centennial standards, the study says, with “background improvements” — roadway changes recommended based on existing traffic problems — in place.

The study evaluated existing traffic conditions based on the SouthGlenn area’s current configuration, and “deficiencies were identified at several locations,” the study says. So the study recommends the following “background improvements”:

• The Arapahoe Road and Vine Street intersection operates below the accepted level of service “in the PM” under existing conditions. To improve the level of service, the implementation of “split phasing” signal timing to allow protected left turns from the northbound and southbound approaches on Vine Street is proposed.

• The Arapahoe Road and York Street intersection is currently being modified to a 3/4 movement intersection. With this change, acceptable operations will be achieved, the study says.

• Due to safety and operational concerns, it is recommended that the University Boulevard and Davies Avenue intersection be converted to a “right-in / right-out” intersection. This is expected to reduce the above-average number of approach turn crashes at the intersection and will improve level of service to an acceptable level, according to the study.

The study also evaluated total traffic based on the addition of the trips that would be generated by the proposed redevelopment, and “no additional mitigation needs were identified,” the study says.

Bunce’s understanding is that the developers’ traffic engineering consultant — Felsburg, Holt and Ullevig — also conducted what’s called a “sensitivity analysis.”

The company did that to determine whether “the additionally conservative approach of adding potential Sears-related traffic from the (study’s) trip-generation table back in to the short-term total would change the outcome of the analysis sufficiently to trigger any additional mitigations due to (level of service) impacts,” Bunce said.

“My further understanding is that the answer to the sensitivity analysis is that the overall outcome did not change as a result, and no additional mitigations were identified as required,” Bunce added.

The statement from the developers’ team said: “The key takeaway (is) that each intersection would still function at an acceptable level of service or better per the city-stated goals.”

Bunce added: “I recognize that some of this may seem odd to folks who aren’t in the (traffic engineering) practice, but I do not have any outstanding concerns regarding the (traffic study) and its conformance to and satisfaction of those items required by the city’s Roadway Design and Construction Standards.”

The traffic study and the city’s approval of the SouthGlenn plan might not be the end of the road for evaluating traffic related to SouthGlenn, according to Bunce.

Because city council approved the SouthGlenn redevelopment project, any future site plans — drawings of how a proposed development will look — will be reviewed by city staff as well as referred to the Colorado Department of Transportation, according to Bunce. 

“At that time, the submitted information will be subject to CDOT’s access permit review and other applicable criteria, and CDOT and the city will then also be able to further evaluate traffic conditions and determine what, if any, traffic or other mitigation might be appropriate,” Bunce said.

For a look at what the traffic study said about “cut-through” traffic in neighborhoods, see the Citizen’s previous story here.

The public can view the traffic study here.

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