{"nulls":"Empty CSV cells / JSON null mean unavailable, never zero. Zero assigned collisions is retained as a count; missing mileage remains null.","lsoa-frost-features.csv":{"grain":"one of 33,755 English LSOA2021 polygons","frostDays":"mean annual air-frost days in 1991–2020, canonically rounded to 6 decimal places","road":"mapped non-fictitious April 2026 OS road length, kilometres","area":"full-resolution clipped polygon area, square kilometres","coverage":"fraction of the relevant length or area intersecting valid climate cells","deciles":"D1 lowest; inverse empirical CDF; fixed England cutpoints separately by weighting; lower interval includes its upper cutoff; missing if coverage fails","variation":"grid counts, minima, maxima and weighted standard deviation describe the climate cells represented; they are not uncertainty intervals","authority":"original UTLA23 code; Barnsley/Sheffield original codes retained after the 2025 boundary change; region-only supplements do not create a current-authority exposure match"},"authority-year-panel.csv":{"grain":"153 inherited English highway authorities × 5 years","motorMiles":"matched annual all-motor vehicle miles; original source units are absolute miles","definiteMotorCollisions":"unique injury collisions containing a declared covered motor vehicle","definiteMotorRatePer100k":"100000 × eligible collision count / matching annual motor miles; null if any inherited quality check fails","rateEligible":"source numerator/denominator eligibility, independent of frost availability","screeningEligible":"rateEligible plus an exact-code usable authority frost feature","balancedScreeningCohort":"screeningEligible in all five years","roadFrostDays":"road-length aggregate of LSOA frost pieces at authority scale; not an LSOA effect estimate","lsoaRoadDecileNCount":"number of LSOAs in fixed national road-frost band N; not a mileage share"},"lsoa-year-inventory.csv.gz":{"grain":"33,755 LSOAs × 5 years","assignedMotorCollisions":"uniquely located primary motor collisions, not proof of complete local outcome coverage","nearBoundaryMotorCollisions":"assigned positions within 10 m of the LSOA boundary","unassignedMotorCollisionsInRecordedAuthority":"source-authority events without unique English LSOA location; cannot be allocated among LSOAs","authorityReportingFlags":"inherited authority reporting/geography reasons","motorMiles":"null for all rows: independent LSOA exposure has not passed","collisionRatePer100k":"null for all rows","frequencyEligible":"false for all rows"},"collision-assignments.csv.gz":{"grain":"one of 513,801 unique GB collision source identifiers","assignment":"assigned, missing_position, ambiguous_boundary or outside_english_polygons","lsoa":"unique LSOA21 full-polygon location, never driver/casualty residence","nearBoundary10m":"positional sensitivity flag for assigned points; not a claim of precise local location"},"weights.csv.gz":{"grain":"LSOA × frost-grid cell; UNOBSERVED sentinel retains uncovered weights","roadMetres":"uniquely allocated mapped network length","areaM2":"intersected polygon area","frostDays":"source cell annual climatological value; empty for UNOBSERVED"}}