Type your starting and ending postcodes. The router identifies the most likely motorway corridor (M1, M25, M6 etc.) and breaks it into 5–10 mile segments matched to National Highways count points.

For multi-motorway journeys (e.g. London to Manchester via M1 and M6), each motorway is analysed separately and combined into the route summary.

Pick "Now" for current conditions, or a specific time window (Morning peak, Evening peak, Off-peak). The comparator pulls historical typical speeds for that exact window so the comparison is fair — Tuesday 17:30 isn't compared to Sunday 04:00.

The summary shows: free-flow journey time (no traffic), typical journey time for your window, current journey time, and the delay vs typical (positive = worse than usual, negative = better).

A delay > 25% of typical is the threshold where the tool starts recommending alternatives. Below that, sticking to the motorway is usually fastest despite the congestion.

The Segment Analysis chart shows current speed vs free-flow speed for each ~5-mile segment. Red bars = severe congestion (<40% free-flow). Amber = moderate (40–70%). Green = free-flowing (>70%).

Look for clusters: 3+ consecutive red bars usually mean an incident or bottleneck — a tactical exit at junction X to rejoin at junction Y can shortcut the worst section.

The Alternative Route panel shows the best B-road or parallel-motorway detour, estimated time and distance, and the time delta vs your motorway route. Detours over 30 minutes are usually worse than waiting unless an incident is verified.

Listen to local radio (BBC local, traffic bulletins) before committing — verified incidents change the calculation; speculative congestion may clear by the time you reach it.

The tool issues a single recommendation: Leave now (delay manageable), Wait 30/60 mins (peak about to subside), Take alternative route (M-route severely degraded), or Postpone (multi-hour delay forecast).

Recommendations are advisory; weigh against your appointment urgency and tolerance for B-road driving.

WebTRIS (Web Traffic Information System) is National Highways' platform exposing data from over 17,000 inductive-loop count points buried in motorway lanes. Each count point reports vehicle counts, average speed, and headway (time between vehicles) at 1-minute intervals.

Speeds are measured directly via dual-loop speed traps in the carriageway, accurate to ±2 mph in normal conditions but degrade in stop-go traffic where vehicles cross loops slowly. The data is aggregated to 15-minute averages for public consumption.

Coverage gaps exist on slip roads and in roadworks zones — temporary contraflow systems often have no live data, leading to "blind spots" in the comparator. We flag segments with stale data in the chart.

Roughly 14% of UK motorway miles are now "smart" — using variable speed limits and (in some sections) dynamic hard-shoulder running. The two main types: Controlled motorway (variable limits, hard shoulder kept) and All-lane running (hard shoulder permanently a live lane).

Average-speed enforcement on smart sections smooths flow and reduces total delay versus dynamic-shoulder sections, but the loss of refuge area increased breakdowns-in-live-lane risk. The 2023 government pause on new all-lane-running schemes was a response to safety reviews.

For travel planning: smart motorways generally have more predictable speeds but lower peak speeds. Variance matters more than mean for journey planning — avoiding red-X lanes (closed lanes) is critical to legal compliance.

Should you detour? Calculate: (extra miles × per-mile fuel cost) + (extra time × your hourly value of time) vs (delay time × your hourly value of time + delay miles × idle fuel cost).

Per-mile fuel cost for petrol: ~14p (40mpg, 145p/litre). For EV: ~6p (4 mi/kWh, 25p/kWh home charge). Hourly time value: typically £15–£40 for personal travel, £30–£80 business travel.

Worked example: 25-min motorway delay vs 12-mile detour adding 18 minutes. Petrol car at £20/h time: motorway = 25/60 × £20 + 25/60 × £1 idle = £8.75. Detour = 18/60 × £20 + 12 × 14p = £7.68. Detour wins — but only if you trust the 18-minute estimate, which on B-roads carries large variance.

The comparator builds "typical" baselines from DfT road traffic counts and rolling 30-day averages on each segment for matching day-of-week and time-of-day. This isolates incident-driven anomalies from normal congestion.

A segment showing 35mph when typical for Tuesday 17:30 is 28mph isn't actually congested — it's slightly faster than usual. A segment showing 22mph when typical is 55mph IS the incident you want to avoid.

Public holidays, school holidays and major events (football, festivals) skew the baseline. We exclude bank holidays from typical calculations but mid-term half-term effects can still cause apparent "delays" that are actually just normal half-term traffic.

For appointments where lateness has high cost (flights, interviews, surgery), optimise for journey-time reliability, not minimum expected time. The 90th-percentile journey time is the meaningful metric — "I want a 90% chance of arriving on time."

On the M25 anticlockwise during Friday evening, the median journey from J16 to J10 might be 38 minutes, but the 90th percentile can be 70 minutes — almost double. Off-peak (10:00–15:00) has tighter dispersion, often 25–32 minute spread.

Strategy: for flight pickups, arrive 90 minutes early and absorb the cost, vs targeting median arrival and risking a missed flight. The tool surfaces journey-time variance bands when historical data supports it.