{
  "version": "mileage-v1",
  "frozenAt": "2026-10-11",
  "regions": ["London", "South East", "South West"],
  "ruralContrast": "South West; a mixed region with substantial rural roads, not an exclusively rural sample",
  "years": [2021, 2022, 2023, 2024],
  "trainingYears": [2021, 2022, 2023],
  "assessmentYear": 2024,
  "geography": "ONS LSOA21 BFC V10 and UTLA23; static OS Open Roads April 2026",
  "scope": "All-motor vehicle miles travelled within each polygon on an access-screened mapped network; not resident, policyholder or vehicle-owner mileage",
  "network": {"excludeFictitious": true, "excludeFunction": ["Restricted Local Access Road"], "publicStatus": "proxy only; OS function does not prove legal public access", "boundaryRule": "exact line intersections; coincident boundary segments assigned once to lexicographically first LSOA"},
  "major": {"source": "DfT both-direction AADF and published link kilometres", "days": "365 or 366", "endpointSnapMetres": 100, "countPointRouteDistanceMetres": 75, "routeToPublishedLengthRatio": [0.8, 1.2], "minimumOwnAuthorityRouteShare": 0.99, "path": "shortest path on same-number OS major-road topology", "fallback": "same authority and road number length; otherwise same authority major-road class length; if unavailable withhold authority-year", "fallbackMaximumForQualityGate": 0.05},
  "minor": {"training": "Counted AADF only, matched to compatible mapped minor class within 50 m; repeated sites inversely weighted by number of training observations", "benchmark": "region x B/other minor x resident settlement mean, shrunk with 20 site-equivalents to class mean", "model": "PoissonRegressor alpha=1, log-density, resident urban fraction, endpoint degree, road class, function, region; standardisation fitted to training only", "forbiddenPredictors": ["frost", "collision counts", "claims", "outcomes"], "selection": "five 20 km geographic block folds on 2021-2023; mean deviance pooled across held-out predictions; benchmark wins if within 1% of model", "annualShares": "static shares from training; all annual growth carried by authority residual; no invented road-class growth factors", "reconciliation": "authority all-road miles minus complete DfT major-road miles; negative/missing residual withheld"},
  "validation": {"assessment": "2024 Counted AADF at sites absent from training is primary; repeated-site results separately reported", "supportedGroupMinimumSites": 30, "supportedGroupMinimum20kmBlocks": 3, "aggregateBiasTolerance": 0.10, "outOfFoldPredictionRequired": true, "allocationValidation": "Count-site prediction checks do not certify within-LSOA allocation; independent representative segment mileage remains unavailable"},
  "stress": {"weights": "minor weights x (1 + delta x (D-5.5)/4.5), renormalised inside each authority-year", "delta": [-0.2, -0.1, 0.1, 0.2], "missingDecile": "neutral weight", "major": "unchanged", "interpretation": "assumption scenarios, not statistical confidence intervals; realised total-mile change differs from input weight change"},
  "outcomes": {"numerator": "Frozen polygon-assigned definite-motor injury collisions counted once", "cohort": "positive mileage, frozen road-frost eligibility and authority rate eligibility across 2021-2024", "comparison": "M0 region + log resident density + resident urban fraction + major mileage share; M1 adds fixed national LSOA D1-D10; Poisson means with exposure offset, trained 2021-2023 and assessed 2024", "calendar": "no fitted year effects; retrospective annual exposure controls total traffic only", "inference": "exploratory conditional sensitivity; authority cluster bootstrap for paired deviance gains, no pricing validation", "majorSubset": "first road motorway/A road, matching number, within 30 m of accepted route; ambiguous count-section matches excluded"},
  "publication": {"rates": "conditional modelled rates only; validated LSOA frequency remains false", "oldPhases": "immutable; no changes to frozen inputs or phase 1-6 results", "independentReview": false}
}