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Vehicle speeds on Welsh motorways

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  • Release date: 17 May 2017
  • 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.

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

Vehicle speeds on the M4 during the morning peak, for cars

Chart: Looking at the morning peak time (between 07:00-10:00), Bridgend westbound had the highest average speed at 73.9 mph. The lowest vehicle speed during the morning peak was in Neath Port Talbot westbound at 58.2 mph, although this would be influenced by the 50 mph speed limit within certain sections of the local authority

Vehicle speeds on the M4 during the evening peak, for cars

Chart: The highest vehicle speeds during the evening peak were travelling eastbound in Bridgend; at 74.2 mph. Monmouthshire westbound had the slowest observed vehicle speeds during the evening peak, at 36.9 mph, 36.0 mph below the vehicle speeds travelling eastbound. This is likely to be due to the impact of having to slow down at the toll.

Key points

  • The M4 and the M48 were at their slowest westbound at the evening peak and at their fastest eastbound during non peak times. The A48(M) was at its slowest eastbound during the evening peak and fastest during the non-peak times westbound. 
  • From April to June 2014 to April to June 2016, vehicle speeds have generally decreased across all three Welsh motorways, although this may be due to other extraneous factors such as sampling changes, weather or the number of road accidents.
  • For the A48(M) and the M4, vehicle speeds are slower in the morning peak during schooldays.
  • In general the M4 is at its fastest through Bridgend. 
  • The M4 is generally at its slowest westbound in the morning peak through Neath Port Talbot and in the evening peak both ways through Newport and westbound in Monmouthshire and Neath Port Talbot.


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