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Vehicle speeds on Welsh motorways

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  • Release date: 19 June 2018
  • Period covered: April to June 2016
This report provides information on vehicle speeds on Welsh motorways, that is the A48(M), M4 and the M48. This is the first statistical publication of motorway speeds in Wales.

Revision note

This experimental statistical article has been revised due to processing errors in calculating average speeds. The original version of the article was available between 17 May 2017 and 19 June 2018.

Since the original release we have continued to explore the quality of the Trafficmaster data, and we have updated the presentation of statistics in this article to match our current understanding.

Car speeds on the M4 during the morning peak

Chart showing average speeds for the stretches of M4 in each local authority in Wales during the morning peak. Neath Port Talbot and Newport are the only local authorities where the average speed is below 60 mph in both directions.

Car speeds on the M4 during the evening peak

Chart showing average speeds for the stretches of M4 in each local authority in Wales during the evening peak. The average speed in Monmouthshire, westbound was 33 mph. This was the slowest average speed for any time, direction or local authority.

The data for this report is taken from in-vehicle global positioning systems (GPS).

Key points

  • Average speeds for the M4 were consistently above 60mph across four out of nine local authorities.
  • Slower average speeds were recorded in Neath Port Talbot and Newport for all directions, during the morning and evening peaks.
  • The A48(M) often saw quarterly average speeds under 60 mph during peak times. The westbound A48(M) routinely saw average speeds under 50 mph during the morning peak.
  • Average speeds on the M48 were consistent in each direction during morning peak hours, but lower westbound for the rest of the day.
  • Analysis suggests a small increase in the average speed on the M4 over the period covered by the data.


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