A third party traffic expert has found that a traffic study for the proposed Bel Air Costco underestimated the number of annual trips to the site by more than 1.3 million, or thousands per day.

Lawrence Green, a professional traffic engineer, conducted the study, funded by an attorney representing the family that owns Klein’s ShopRite — a grocery store located less than a mile from the proposed Costco development.

Green’s study found that traffic to the site was underestimated in data that the Harford County government is using to arrange traffic improvements near the site.

Costco has proposed construction of a 152,000 square-foot store with 821 parking spots and a 24-pump gas station at the corner of Plumtree and Emmorton roads. Costco is a membership-only warehouse club that sells groceries and home goods. The proposed Costco is surrounded by numerous commercial lots. The plan’s Traffic Impact Study shows two fast-food restaurants ranging from 2,000 to 4,000 square feet, two 14,500 square-foot high-turnover sit-down restaurants and a 5,106 square-foot car wash occupying the lots.

Since the plans were announced last year, residents have voiced concerns about potential traffic congestion and traffic safety issues.

According to Harford County code, traffic impact studies are based on data from the Institute of Transportation Engineers Generation Manual, a nationally accepted, industry standard document. The institute has numerous classifications for different stores with Costco falling under the classification of “discount clubs.”

Green said ITE has been collecting traffic data on discount clubs since the 1980s and that he felt the projected trip generation numbers outlined in the county’s study were “pretty low.”

“My intuition was that the rates were pretty low, so I did an internet [search] and found a firm that has done a lot of traffic work for Costco,” Green said.

That firm is Kittelson and Associates, which has completed over 15 traffic studies for Costco stores identical to the square footage and number of fuel pumps proposed for the store in Bel Air, Green said. Traffic Concepts Inc. completed the traffic study for the Bel Air Costco.

Comparing Kittelson and Associates’ report to the report Harford County is using for the proposed development, Green found that all of the traffic data points Harford County is using are significantly lower than the data generated by Costco’s reports.

The data is as follows for weekday trips:

  • ITE data weekday daily trips generated – 6,883 trips
  • Costco data weekday daily trips generated – 10,624 trips

Peak morning hour weekday trip:

  • ITE data weekday AM peak hour – 130 trips
  • Costco data weekday AM peak hour – 215 trips

Peak afternoon hour weekday trips:

  • ITE data weekday PM peak hour – 448 trips
  • Costco data weekday PM peak hour – 931 trips

Saturday trip generation:

  • ITE data Saturday daily trips generated – 8,713 trips
  • Costco data Saturday daily trips generated – 12,719 trips

Sunday trip generation:

  • ITE data Sunday daily trips generated – 5,458 trips
  • Costco data Sunday daily trips generated – 7,968 trips

Green raised concerns about the proposed traffic enhancements that the Traffic Impact Study proposed for nearby roadways. He said the proposed enhancements are based on the ITE data and are still on the “threshold of adequacy.”

“I looked at the traffic enhancements and they are proposing the best they can given the amount of right of way, but they are right on the threshold of adequacy so if you’re doubling the trips, it is going to blow the enhancements out of the water,” Green said. “What happens with traffic is once you reach the tipping point of adequacy, it decays exponentially.”

Green said the ITE advises traffic experts to use more accurate data if available, prompting him to contact Harford County with his findings.

“The ITE doesn’t say you have to use their data but a lot of times it is the best available, but studying 15 plus sites is way better than ITE,” Green said. “It’s not even close.”

He that “with a bit of certainty,” if the traffic analysis uses the more accurate rates, more road improvements will be needed — something he said he doesn’t think will be feasible given the amount of space the county and State Highway Administration has to work within the area.

“Costco is fully aware that they are way underestimating their trips,” Green said. “Once it’s built, they can cry to the state and the county telling them they need to help with traffic.”

The Director of Planning and Zoning for Harford County, Shane Grimm, responded to Green’s letter advising him of the report and said all traffic studies are done in accordance with the county code and traffic impact analysis guidelines.

Grimm emphasized that the ITE is “nationally accepted” and “utilizes information, data and statistics that are submitted to ITE for consideration.”

“I am not blaming Traffic Concepts for using the ITE report because they are going off of Harford County guidelines but since this other data is available, they really should be using it because it is much more accurate,” Green said. “They are sticking by their guns for the ITE data.”

As of February, the Costco developers have not resubmitted a revised Traffic Impact Study addressing potential concerns outlined by county and state entities.

County officials did not immediately respond to a request for comment.

Have a news tip? Contact Matt Hubbard at mhubbard@baltsun.com, 443-651-0101 or @mthubb on X.