Why is average speed not just the average of each speed?

Average speed is total distance divided by total time, not the arithmetic mean of speeds. If you drive 60 miles at 30 mph (2 hours) and 60 miles at 60 mph (1 hour), your average speed is 120 miles / 3 hours = 40 mph, not 45 mph. You spend more time at the slower speed, so it has a greater effect.

How do average speed cameras work in the UK?

Average speed cameras (SPECS, VECTOR) use ANPR to record your number plate at two points and calculate the time taken. They divide the distance by your time to get your average speed. They operate 24/7 and cover distances from a few hundred metres to over 10 miles. They are common in roadworks and on the A9 in Scotland.

What is a good average speed for a UK road trip?

For UK road trips, expect averages of 40-55 mph on mixed routes. Pure motorway journeys might average 55-65 mph. Cross-country routes with towns and villages average 30-40 mph. Allow extra time for breaks, fuel stops, and traffic delays.

Can I use this to check average speed camera zones?

Yes, if you know the distance between average speed camera installations and the speed limit, you can calculate the minimum time needed to travel between them without exceeding the limit. However, always drive safely and within the speed limit rather than trying to calculate the minimum time.

What affects average speed on a journey?

Factors include road type, traffic density, time of day, weather conditions, roadworks, number of junctions and roundabouts, and speed limits. Urban sections dramatically lower your average even if you drive fast on open roads.

CarCalcs

Average Speed Calculator — Multiple Segments

Calculate your average speed from multiple journey segments with different speeds.

Segment 1 Distance

Segment 1 Speed

Segment 2 Distance

Segment 2 Speed

Segment 3 Distance

Segment 3 Speed

Segment 4 Distance (optional)

Segment 4 Speed (optional)

How We Calculate This

The Formula

Average Speed = Total Distance / Total Time

Where Total Time = Sum of (Distance / Speed) for each segment

Why Not Arithmetic Mean?

The harmonic mean (used when distances are equal) or the distance-weighted calculation (used here for different distances) gives the true average. Simply averaging the speeds gives an incorrect result because you spend different amounts of time at each speed.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Actual figures may vary based on driving conditions, vehicle specifications, and other factors.