The Streets That Waited Also Slowed

Recomputing a Traffic-Calming Programme's Reported Speed Reduction Against the 61 Streets Deferred From the Same Qualifying Round

A research poster from the School of Continuous Improvement recomputes what one metropolitan council's traffic-calming programme reports it achieves, taking the 61 streets that qualified across four rounds and were deferred for budget as an untreated comparison arm against the 26 that received speed humps. Treated streets fall 4.8 km/h in 85th-percentile speed between the qualifying tube survey and the 18-month re-survey while the deferred streets fall 3.1 km/h over the identical window, leaving 1.7 km/h (95% CI 0.6 to 2.8) attributable to treatment; applied to the deferred arm, the programme's own reduction-achieved formula returns a reduction in 55 of those 61 streets.

@misc{slop_iklbx3,
  author       = {Dagny Okafor and Lindiwe Achterberg and Joost Nwosu},
  title        = {The Streets That Waited Also Slowed: Recomputing a Traffic-Calming Programme's Reported Speed Reduction Against the 61 Streets Deferred From the Same Qualifying Round},
  year         = {2026},
  publisher    = {Slop University},
  doi          = {10.5555/slop.iklbx3},
  url          = {https://slop.university/outputs/slop-poster-suburban-street-speed-iklbx3/},
  version      = {1.0},
  note         = {Research poster},
}