# Three-period ITS method QA

Generated: 2026-06-11T00:03:39

## Sample
- Paired roads (HC full/bounded/spatial + both events): 791
- Roads with valid 3-period panel: 662
- Skipped at panel build / minimum-count filters: 129
- included: 662
- no usable/common crash match: 127
- no crashes in the complete-month study window: 2
- corridor: 26
- local_street: 636

## Pooled results (ADT offset + COVID covariate sensitivity)

| Road class | Response | Reduction IRR (95% CI) | Reduction p | Reversal IRR (95% CI) | Reversal p | N obs |
|---|---|---|---|---|---|---|
| corridor | total | 0.920 (0.788-1.076) | 0.298 | 1.160 (0.951-1.417) | 0.144 | 129 |
| corridor | injury | 1.122 (0.849-1.483) | 0.419 | 1.214 (0.836-1.762) | 0.308 | 129 |
| local_street | total | 0.921 (0.769-1.103) | 0.370 | 0.000 (0.000-485165195.410) | 0.999 | 131 |
| local_street | injury | 1.318 (0.939-1.850) | 0.110 | 0.000 (0.000-485165195.410) | 0.999 | 131 |

## Sensitivity analyses (3-period)

| Road class | Response | Sample | Reduction IRR | Reversal IRR |
|---|---|---|---|---|
| corridor | total | adt_covid | 0.920 | 1.160 |
| corridor | total | exclude_covid_months | 0.816 | 1.182 |
| corridor | total | uncontrolled | 1.102 | 1.077 |
| corridor | injury | adt_covid | 1.122 | 1.214 |
| corridor | injury | exclude_covid_months | 1.133 | 1.433 |
| corridor | injury | uncontrolled | 1.304 | 1.123 |
| local_street | total | adt_covid | 0.921 | 0.000 |
| local_street | total | exclude_covid_months | 0.982 | 0.000 |
| local_street | total | uncontrolled | 0.953 | 0.000 |
| local_street | injury | adt_covid | 1.318 | 0.000 |
| local_street | injury | exclude_covid_months | 1.288 | 0.000 |
| local_street | injury | uncontrolled | 1.432 | 0.000 |

## 2-period pooled ITS (broader sample, one event per road)

| Road class | Event | Response | Sample | Level IRR (95% CI) | p | N obs | N roads |
|---|---|---|---|---|---|---|---|
| corridor | reduction | injury | adt_covid | 0.770 (0.655-0.905) | 0.002 | 19488 | 406 |
| corridor | reduction | injury | uncontrolled | 0.962 (0.820-1.129) | 0.637 | 19488 | 406 |
| corridor | reduction | total | adt_covid | 0.834 (0.757-0.917) | 0.000 | 26448 | 551 |
| corridor | reduction | total | uncontrolled | 1.065 (0.969-1.170) | 0.194 | 26448 | 551 |
| local_street | reduction | injury | adt_covid | 0.981 (0.710-1.357) | 0.908 | 17664 | 368 |
| local_street | reduction | injury | uncontrolled | 0.949 (0.687-1.311) | 0.752 | 17664 | 368 |
| local_street | reduction | total | adt_covid | 1.034 (0.874-1.223) | 0.699 | 40416 | 842 |
| local_street | reduction | total | uncontrolled | 1.018 (0.861-1.204) | 0.837 | 40416 | 842 |
| corridor | reversal | injury | adt_covid | fit failed | -- | 1488 | 31 |
| corridor | reversal | injury | uncontrolled | 1.008 (0.653-1.554) | 0.973 | 1488 | 31 |
| corridor | reversal | total | adt_covid | 0.989 (0.787-1.244) | 0.927 | 1488 | 31 |
| corridor | reversal | total | uncontrolled | 1.064 (0.846-1.337) | 0.596 | 1488 | 31 |
| local_street | reversal | injury | adt_covid | fit failed | -- | 29624 | 644 |
| local_street | reversal | injury | uncontrolled | 0.572 (0.318-1.031) | 0.063 | 9384 | 204 |
| local_street | reversal | total | adt_covid | 0.969 (0.716-1.312) | 0.839 | 19596 | 426 |
| local_street | reversal | total | uncontrolled | 0.989 (0.731-1.337) | 0.940 | 19596 | 426 |

Sparse supplementary fits that do not identify a covariance matrix are retained as explicit failed rows rather than omitted.