Skip to main content

Gera Road Risk Index (GRRI) — full methodology

Published 2026-06-20 · Data period: 2022–2023 · 363 local authorities

What the GRRI measures

The Gera Road Risk Index (GRRI) is a KSI-severity-weighted road-casualty rate per 1,000 licensed vehicles, computed per Great Britain local authority. It answers the question: given how many vehicles are registered here, how often do serious road casualties occur? A higher GRRI indicates a higher road-casualty burden relative to vehicle ownership — a signal that is directly relevant to motor and vehicle insurance risk.

Step-by-step computation

  1. 1

    Obtain vehicle counts (DfT VEH0105)

    Download DfT Vehicle Licensing Statistics 2023 (table VEH0105 — Licensed vehicles by body type, fuel type, keepership and local authority, Great Britain). Select the row where Body type = "Total", Fuel = "Total", Keepership = "Total" and period = Q4 2023 (end-December 2023). Units are thousands of vehicles.

  2. 2

    Obtain casualty counts (DfT STATS19)

    Download the DfT STATS19 collision-level CSV (last 5 years). Filter to collision_year ∈ {2022, 2023}. Aggregate by local_authority_ons_district, summingnumber_of_casualties separately for collision_severity = 1 (fatal), 2 (serious), and 3 (slight).

  3. 3

    Compute KSI-weighted rate

    For each local authority, compute the annual KSI-weighted rate:

    ksi_weighted_per_1000 =
  (3 × killed_2yr + 2 × serious_2yr + 1 × slight_2yr)
  / 2                                    ← annual average
  / vehicles_thousands_q4_2023           ← per thousand vehicles

    Fatalities are weighted 3×, serious injuries 2×, slight injuries 1×, reflecting the NHS and DfT “STATS19 severity” scale. Dividing by licensed vehicles (not population) normalises for vehicle ownership, not just area size. The 2-year average smooths year-to-year volatility.

  4. 4

    Assign GRRI band (1–10)

    Rank all 363 local authorities by ksi_weighted_per_1000 ascending. Assign GRRI band 1–10 by percentile decile:

    • GRRI 1 = bottom decile (safest ~10%; lowest KSI rate)
    • GRRI 5–6 = median band
    • GRRI 10 = top decile (highest risk ~10%; highest KSI rate)

    Each band covers approximately 36 of the 363 local authorities. The average KSI-weighted rate across all areas is 4.772 per 1,000 vehicles per year.

Key dataset figures (2022–2023)

Local authorities in dataset363
CoverageEngland, Wales, Scotland (Great Britain)
Vehicle dataDfT VEH0105 Q4 2023 (licensed, all types/fuels)
Casualty dataDfT STATS19 2022–2023 (2-year average)
GB average KSI-weighted rate4.772 per 1,000 vehicles per year
Highest GRRI areaCity of London (10/10)
Lowest GRRI area (safest)Stockport (1/10)

Interpretation caveats

  • City of London has the highest raw KSI-weighted rate (79.5 per 1,000 vehicles) because its licensed vehicle base is very small (3.1k) while pedestrian and cyclist casualties in the dense Square Mile are high. This is a well-documented statistical phenomenon for dense urban cores — the GRRI accurately reflects this structural difference.
  • The GRRI measures road-casualty burden relative to vehicle ownership. Areas with very low vehicle registrations but high through-traffic or pedestrian activity will score higher than their absolute casualty count alone would suggest.
  • The index uses licensed vehicles as the denominator, not road miles travelled. Insurance underwriters use additional factors including vehicle mileage, driver age, and NCB. The GRRI is an area-level risk context signal, not a premium predictor.
  • STATS19 figures reflect police-recorded collisions only; minor collisions not reported to police are excluded. Under-reporting is highest for slight injuries.

Licence and attribution

The underlying data (DfT VEH0105 and DfT STATS19) are published by the Department for Transport under the Open Government Licence v3.0. Contains public sector information licensed under the Open Government Licence v3.0. The Gera Road Risk Index formula, band assignment methodology, and derived per-authority index values are copyright GeraSure / Gera Services Ltd 2026. You may quote GRRI values with attribution: “Gera Road Risk Index, GeraSure, 2026 (source data: DfT VEH0105 + STATS19, OGL v3.0)”.

Get notified when GRRI updates

We refresh the GRRI annually when DfT publishes new STATS19 data. Join the waitlist to receive the updated index and any insurance-context reports derived from it.

Join the update waitlist

← View road risk by local authority