Gera Traffic Pressure Index — Methodology
Full reproducible specification for the GTPI/10 index covering 153 English local authorities. Last updated using 2025 data.
1. Purpose
The Gera Traffic Pressure Index (GTPI/10) is a single per-local-authority score that combines three dimensions of road traffic stress from DfT open data: how fast traffic has grown over 10 years, how much of that traffic is heavy freight, and how intensively the road network is monitored (a proxy for road density).
It is designed to help renters and buyers compare areas on a metric that captures residential road environment quality more completely than raw vehicle counts alone. A high-AADF road in an area where traffic has declined and HGV share is lowis meaningfully different from the same AADF in a logistics corridor with growing freight volumes.
Important: GTPI is a location comparison tool, not a road-safety assessment. The underlying data is official DfT road traffic statistics (OGL v3.0); the composite formula is GeraRent's own and is not endorsed by the Department for Transport.
2. Data Sources
Source 1 — DfT AADF Count-Point Data (Primary)
File: dft_traffic_counts_aadf.zip → dft_traffic_counts_aadf.csv
URL: https://roadtraffic.dft.gov.uk/downloads
Content: ~600,000 rows. Each row = one count-point in one year (2000–2025). Key fields: count_point_id, year, local_authority_code, all_HGVs, all_motor_vehicles.
Coverage: 153 English local authorities with 2025 data.
Licence: Open Government Licence v3.0.
Source 2 — DfT Local Authority Road Traffic Estimates
File: local_authority_traffic.csv
Content: Per-LA per-year road network length (link_length_km), used to compute count-point density (count-points per 100km of road).
Licence: Open Government Licence v3.0.
Source 3 — DfT Count Point Locations
File: count_points.zip → count_points.csv
Content: Count point identifiers with region and LA assignment (region_name, region_ons_code). Used for region attribution.
Licence: Open Government Licence v3.0.
3. Formula
Step 1 — Per-LA AADF aggregation
Step 2 — 10-year growth trend
latest = most recent year (2024 or 2025); ref = 2014 (or nearest in 2012–2016). If |trend_pct| > 60%, the LA likely changed boundaries and the trend is artefactual — it is flagged as imputed and set to the national median trend score (5.46/10). This affects 6 of 153 LAs (new authorities created post-2014).
Empirical range: -34.7% to 40.2% across 153 LAs.
Step 3 — Count-point density
Higher density = more intensively monitored road network = more road capacity per area km = generally higher urbanisation. This acts as a proxy for road network intensity (urban vs rural character). Range: 2.4 to 70.2 per 100km.
Step 4 — Min-max normalisation
Each sub-score normalised independently across all 153 LAs. Higher sub-score = higher pressure in that dimension.
| Sub-score | Min (raw) | Max (raw) | Weight |
|---|---|---|---|
| trend_score (10-yr growth) | -34.7% | 40.2% | 40% |
| hgv_score (HGV share) | 1.4% | 13.1% | 35% |
| density_score (CP/100km) | 2.4 | 70.2 | 25% |
Step 5 — Composite GTPI
Weight rationale: traffic growth (40%) is the primary signal because it reflects whether an area's roads are under increasing stress. HGV share (35%) captures freight-driven amenity impact (noise, vibration, air quality). Count-point density (25%) provides an urbanisation proxy — it is the least directly interpretable dimension but helps distinguish genuine rural low-traffic from data-sparse areas.
4. GTPI Banding
| Band | GTPI range | Interpretation |
|---|---|---|
| Very Low | <2.5 | Islands, very rural, or declining-traffic areas. Minimal freight, low network density. |
| Low | 2.5–4.0 | Below national average pressure. Lower HGV share and/or slower AADF growth. |
| Moderate | 4.0–5.5 | National average range. Mixed urban/suburban character. |
| High | 5.5–7.0 | Above-average pressure. Notable freight corridors or strong growth. |
| Very High | ≥7.0 | Highest pressure. Intensive freight use, strong AADF growth. |
National average: 3.4/10. Empirical range across 153 English local authorities: 1.7 – 6.5.
5. Limitations and Honest Caveats
- Count points are not evenly distributed: DfT count points are placed on classified (A/B) roads; minor roads and residential streets are not captured. HGV share from count points reflects major-road freight, not total road network exposure.
- Boundary changes (6 LAs): Councils created after 2014 (e.g., Cumberland, Westmorland and Furness) cannot have valid 10-year trends. Their trend sub-score is imputed to the national median and flagged visually on every page. HGV share and density are still real.
- Old Cumbria excluded: E10000006 (pre-reorganisation Cumbria) is excluded — it was superseded in April 2023 by Cumberland and Westmorland and Furness. Its data would double-count the area.
- avg_aadf is an unweighted mean across count points: Count points vary in road importance (A-road vs B-road). A local authority with one heavily-trafficked motorway junction count and many minor B-road counts will have a lower avg_aadf than the junction alone suggests.
- Annual figures only: Peak-hour and day-of-week distributions are not captured. AADF is the annual 24-hour average across all days.
- Scotland and Wales excluded: This index covers English local authorities (ONS code prefix E*) only.
6. Data Licence and Reuse
Source data is published under the Open Government Licence v3.0 by the Department for Transport. The licence permits free reuse with attribution. The Gera Traffic Pressure Index — the composite formula and resulting scores — is GeraRent's own work and is not endorsed by DfT or any government body. We publish the full methodology here so the index is independently reproducible.
Attribution required: “DfT Road Traffic Statistics (AADF), 2025 / Gera Traffic Pressure Index, GeraRent (gerarent.com/traffic-pressure-index), Open Government Licence v3.0.”
Compare areas with real traffic pressure data
Use the Gera Traffic Pressure Index to find the quietest areas to rent in England.
See all 153 English local authorities →National average GTPI: 3.4/10. Data: DfT dft_traffic_counts_aadf.zip + local_authority_traffic.csv + count_points.zip,2025. Open Government Licence v3.0. Methodology published .