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Highway Code guidance is a break of at least 15 minutes every 2 hours of driving. Average speeds already account for junctions and slower stretches; add contingency for motorway roadworks and rush hours.
What The Journey Time Calculator Works Out
- Driving time: distance divided by a realistic average speed. Even a clear motorway trip averages about 60 mph once junctions, services and the slower ends of the journey are included; mixed A-roads run nearer 40 to 50 and urban driving 20 to 25. A 120-mile motorway trip is therefore a 2-hour drive, not the 1 hour 43 that dividing by 70 suggests.
- Total journey time: driving time plus the Highway Code's recommended break of at least 15 minutes every 2 hours of driving. Tiredness causes up to a fifth of serious collisions, with the highest-risk windows in the early hours and mid-afternoon.
- If you leave at 9:00: the arrival time for a 9:00 departure, as a quick sanity check against the sat-nav's optimism.
- Departure time (advanced): enter your real departure hour and minutes to get the arrival time for that trip, with any extra stops (fuel, charging, pick-ups) added. Plan fuel or charging stops into the same breaks rather than as extra ones.
- Custom speed, break interval and length (advanced): override the dropdown speed and the 2-hour / 15-minute break pattern. A 50 mph average-speed roadworks section or a car full of children both justify different settings.
- Contingency for traffic (advanced): adds a percentage to the whole journey for predictable friction: urban rush hours (roughly 7:30 to 9:30 and 16:30 to 18:30), Friday afternoons on motorways and school holidays around the coast. 10% to 20% is typical; the worst-case card shows the later arrival.
- Fuel cost (advanced): distance divided by your MPG, converted through the UK gallon (4.546 litres) at the pump price you enter. At 40 mpg and current petrol prices that is about 19p a mile, so a 120-mile trip is roughly GBP 23.
- Latest departure to arrive by 9:00 (advanced): works backwards from a 9:00 arrival using the worst-case time, useful for meetings and early flights.
- Timeline table (advanced): the clock time and mileage of each planned break, so you can pick services in advance rather than stopping wherever the next sign says.
Source and further reading: GOV.UK: The Highway Code.