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City engineer outlines alley traffic‑calming pilot after speed studies in two neighborhoods
Summary
Lewisville staff proposed a cautious pilot for vertical‑deflection devices in long, straight alleyways after speed studies showed 85th‑percentile speeds near 20 mph where the prima facie alley speed is 15 mph; staff emphasized high thresholds, resident petitions and coordination with emergency services.
City Engineer Brett Bourgeois told the Lewisville City Council on March 2 that staff is proposing a pilot program to test vertical‑deflection traffic‑calming devices in long, straight alleyways after multi‑day studies found speeds higher than expected.
Bourgeois said studies on two alleyways—Piedmont and Lake Crest—showed 85th‑percentile speeds around 20 miles per hour compared with the prima facie alley speed of 15 mph under state law, and recorded roughly 90 vehicles over multiple days on Piedmont (average daily trips 20–25) and about 440 vehicles on Lake Crest (average daily ~140). "We saw that the 85th percentile ... was 20 miles per hour, which is considerably higher than the 15 miles per hour," Bourgeois said during the workshop presentation.
Bourgeois described three elements of the proposed approach: strict data thresholds to trigger devices, resident consent, and a phased, reversible installation. Staff proposed thresholds that include a majority of drivers exceeding the prima facie speed (staff referenced a 50% threshold), a separate threshold tied to 85th‑percentile speeds around 20 mph, and an 80% petition of affected residents in favor of installation before the city proceeds. "We would like to see a petition by completed by the residents of 80% of the residents on the alleyway that are gonna be impacted agreeing to installing these devices," Bourgeois said.
On treatment and durability, Bourgeois said initial installations would favor bolt‑down speed cushions so the devices can be removed or adjusted; cast‑in‑place options would remain a later, more permanent choice if the pilot proves effective. He also said staff will consult the city’s trash contractor and the fire marshal on spacing and design, and will re‑measure speeds after three to six months of operation to determine whether the devices worked as intended. "If they don't like them, we're more than willing to take them out," he said.
A resident, Karl Krause, addressed the council during the public‑comment portion and urged action in his alley, saying the downhill grade there produces much higher speeds: "I've seen people probably going over 25 miles an hour," Krause said. Krause supported installing more signage and engineering fixes and confirmed he has been coordinating with staff on the issue.
Council members pressed staff on preventing drivers from accelerating between devices and on whether repeated installations could open a floodgate of requests citywide. Bourgeois said the pilot and high petition thresholds are designed to limit installations to a small number of unique alleyways that meet the technical criteria.
Next steps: staff will engage with residents and service providers to finalize design choices, collect petitions where residents express support, and return to council with implementation details and an analysis after the pilot monitoring period.
