Gaithersburg staff propose tighter trip thresholds and delay-based congestion standard for traffic impact studies

Gaithersburg City public-works staff presented draft changes to the city's traffic impact study (TIS) standards at a July 13 mayor and council work session, proposing a modest change to the trip threshold and a shift from a critical-lane-volume test to delay-based congestion metrics.

Brian Fields, the city's director of public works, told the council the TIS is "an engineering report that analyzes how a new development will affect the surrounding transportation system" and that its aim is to identify capacity, safety or operational issues before construction. He said the city currently requires a TIS when a site generates a minimum of 30 peak-hour trips (combined ingress and egress), which is lower than common state and national comparators.

Doug Smith, the city traffic engineer, summarized the proposed technical changes: instead of the current 30 combined-trips threshold, the draft would require a study when a site generates 25 or more peak-hour trips entering OR 25 or more peak-hour trips exiting, a change intended to capture projects that concentrate trips in one direction (such as offices). Smith also recommended replacing the city's critical lane volume (CLV) pass/fail test (the city's existing CLV threshold is about 1,450) with Highway Capacity Manual delay analysis. Under the proposed standard the average delay per vehicle at a signalized intersection would need to be no more than 59 seconds, with individual movement delay capped at 80 seconds and stop-controlled movement at 35 seconds.

Nut graf: Staff said the changes reflect updates to national guidance and to the Institute of Transportation Engineers trip generation manual, which now differentiates trip generation by surrounding context (for example, "dense multiuse urban" vs. "general urban-suburban"). That context-based approach can reduce trip estimates for walkable, mixed-use neighborhoods; staff said the proposed standards will allow such reductions where criteria in the ITE manual are met, rather than applying a citywide average.

Councilmembers raised questions about how context would be selected and whether applicants could choose the classification that gives the more favorable (lower) trip count. Smith said applicants often select a more conservative option that shows higher volumes to avoid redoing studies, but he acknowledged discretion is used in scoping study areas and in downtown locations where staff wants to avoid pushing proposals toward road widening. Fields said the TIS process includes iterative reviews and scoping letters at the start of each study: "we work all of that out usually ahead of time," he said.

Residents and commissioners pressed staff on related issues. Resident Nick Glenn urged against a blanket designation of Old Town as "dense multiuse urban," saying prior use of that context lowered trip counts for a large apartment project and drew public pushback. Staff responded that the update makes the city's reliance on the ITE manual more explicit and that some recent projects (including Park and Brooks) will submit new TIS reports for review under the draft standards.

Council members also recommended adding clearer documentation to development packets that explains scoping and the iterative steps staff took to reach an approved TIS; one member suggested a short bullet list or staff memo summarizing the review chronology so the public can see how staff and applicants resolved outstanding issues.

In addition to the TIS technical changes, staff briefed the council on two traffic initiatives: early results from a 20-mile-per-hour neighborhood speed-limit pilot and new data purchases. Smith said follow-up studies of four pilot neighborhoods showed median and 85th-percentile speeds stayed largely unchanged, while 95th-percentile speeds fell by about 0.75 mph and maximum speeds dropped about 5 mph; staff proposed adding up to five similar zones, including parts of Kentlands and Lakelands. The city also bought two StreetLight Data packages: a 12-month connected-vehicle "near-miss" dataset (hard braking/acceleration) to identify safety hotspots, and origin-destination trip data to analyze cut-through routes and coordinate signals.

Quotes from the public illustrated local concerns. "I'm all for flexibility, but that that's certainly not something that should be approved," Nick Glenn said of a blanket Old Town dense designation. Joan Berkowitz of Park Avenue urged that "anything that can slow down the cars" on her block would be helpful and asked the council to consider Park Avenue for the 20 mph program.

Staff indicated they will revise the draft TIS standards based on council input and return a final proposal for council review and vote at a later meeting. The work session closed with the mayor announcing the next regular meeting on July 20.

Ending: No formal votes were taken at the July 13 work session; the presentation and discussion were staff briefings and public comment, and staff said they will bring revised standards back to the council for formal consideration.