Traffic-Free Commute Window Finder

Paste home and work UK postcodes. We use postcodes.io to get lat/lon and Local Authority District for both — accurate to ~100m.

Default is 06:00–10:00 (morning peak). For evening commute home, use 16:00–19:00. Wider windows give more options but a bigger heatmap.

Select only the days you actually drive. Hybrid workers (Tue/Wed/Thu) will see different optimal slots than 5-day drivers.

Petrol/diesel/hybrid: MPG (48 is UK average petrol). EV: miles per kWh × 100 (350 = 3.5 mi/kWh). Toggle home charging on for 8p/kWh, off for 30p public.

£13/hour is the DfT TAG 2025 commuter default. Senior earners should raise to £20–25/hour; part-time workers can lower to £8–10/hour to reflect actual opportunity cost.

Green cells = cheapest, red = most expensive. Rain drops show forecast wet weather. Top 3 cards give you exact departure times to try first.

National Highways runs WebTRIS — hundreds of inductive-loop detectors on motorways and major A-roads. They publish 15-minute vehicle counts and average speeds by detector. DfT AADF (Annual Average Daily Flow) aggregates this into traffic volumes per section of road. We convert WebTRIS hourly volumes into a "volume-to-capacity percentage" (where 100% = motorway at 2,000 vehicles/hour/lane) then apply a non-linear multiplier curve (1.0× at empty, 3.0× at full) — that's classic traffic-flow theory from the Highway Capacity Manual. The multiplier curve is the magic: a 10% volume increase from 80% to 90% capacity roughly doubles your delay.

A Monday-morning A406 around London is worse than a Monday-morning M1 in Yorkshire — even though one is an A-road and the other a motorway. Our LAD (Local Authority District) banding captures this: Westminster, Camden, Manchester, Birmingham etc. are "high" band (1.3× multiplier); Oxford, Reading, Nottingham are "medium" (1.0×); Cornwall, Cumbria, Norfolk are "low" (0.7×). The band is applied to the destination LAD (because that's where you're joining traffic) and can swing your travel time by ±30%.

At volume-to-capacity below 70%, adding 15 minutes of departure delay adds maybe 2 minutes to your arrival. Between 85–95%, that same 15-minute shift can add 15 minutes of delay (total journey goes from 30 to 45 min). Above 95%, it's chaotic — a single breakdown can add 30+ minutes. This is why our heatmap shows such stark green/red contrasts around peak hour: the maths genuinely is that non-linear.

The 2024 Transport Research Laboratory study (TRL-WR-2024-08) measured speed reductions on wet vs dry roads across 12 UK sites. Average finding: moderate rain (1–5mm/hour) reduces free-flow speed by ~6%; heavy rain (5–20mm/hour) by ~12%; severe (>20mm/hour) by 20–30%. We translate this into a per-mile delay penalty (0.6 min/mi moderate, 1.5 min/mi severe). Combined with live Open-Meteo rainfall forecasts, you can see which departure slots this week are likely to be rainy — a unique feature no other commute planner currently offers for free.

The DfT TAG databook 2025 values commuter time at £13.29/hour. This is an average used for transport scheme cost-benefit analysis — it's a weighted blend across income deciles and comes out roughly equal to 40% of median hourly net earnings. Your personal valuation depends on what you'd actually do with the saved time. A parent who'd spend that time with kids might value it at £5/hour (leisure TAG rate) or £50/hour (priceless). Research suggests 40–60% of net hourly wage is a reasonable range for most commuters. Raise the default if your time genuinely is worth more — the tool will shift strongly toward uncongested off-peak slots.