A Staggered-Adoption Difference-in-Differences Analysis of Driver-Feedback Speed Signs Across 61 Residential Streets, Against a Rotation Interval Set by Trailer Availability
A paper from the School of Continuous Improvement estimates what a council's rotating fleet of driver-feedback speed signs achieves across a full deployment rather than its opening fortnight. Sixty-one residential streets received a trailer-mounted sign between March 2023 and February 2026 in an order set by trailer availability, with permanent tube counters recording speeds throughout. Group-time treatment effects estimated against not-yet treated streets show mean speed falling 2.41 km/h in the first fortnight, attenuating monotonically, and reaching a precisely estimated null from week eleven (-0.09 km/h, 95% CI -0.38 to 0.20). The fleet's median deployment duration is 11.6 weeks, a figure set by the depot's rotation roster, so each sign is relocated within a fortnight of the point at which its effect stops being measurable. An expression module fitted to fourteen deployments accounts for 0.11 km/h of the effect and is retained for completeness.
| Authors | Torun Ezeigwe , Thandiwe Solberg , Joost Nwosu |
|---|---|
| School | School of Continuous Improvement |
| Output type | Research paper |
| Published | |
| DOI | 10.5555/slop.07lgun |
| Pages | 6 |
| Cited by | 25 outputs |
| Version | 1.0 |
| Licence | CC BY 4.0 |
Cites
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Cite as
@misc{slop_07lgun,
author = {Torun Ezeigwe and Thandiwe Solberg and Joost Nwosu},
title = {Eleven Weeks, Then Nothing: A Staggered-Adoption Difference-in-Differences Analysis of Driver-Feedback Speed Signs Across 61 Residential Streets, Against a Rotation Interval Set by Trailer Availability},
year = {2026},
publisher = {Slop University},
doi = {10.5555/slop.07lgun},
url = {https://slop.university/outputs/slop-paper-the-flashing-roadside-07lgun/},
version = {1.0},
note = {Research paper},
}