A48 Traffic - SPEEDS!

This page details the results of speed surveys on the A48.  Details of the Capacity and possible Improvements to the A48 can be found via these links:

  • In 2011, 3,267 people were killed or seriously injured in crashes where speed was a factor 
  • The risk of death is approximately four times higher when a pedestrian is hit at 40mph than at 30mph
The volume and speeds of motorised traffic can be seen below.  The raw data shows vehicles travelling through St Nicholas at speeds in excess of 60mph, often at night, but also during the day, for example between 4 and 5pm.

Highways engineers look at the 85th percentile, which gives the speed that 85% of motorised traffic travels at to determine whether there is an issue with speed.  For the first site close to Dyffryn Lane, this is 32.7mph, and the second towards Trehill, 38.3mph.  At this time, unlike in Bonvilston (where speeds during the day have been recorded at around 70mph), speed of traffic in St Nicholas is not a concern to the highways engineers.

7-day two-way 85th percentile speed = 32.7 mph
7-day eastbound 85th percentile speed = 31.1 mph
7-day westbound 85the percentile speed = 33.8 mph

7-day two-way 85th percentile speed = 38.3 mph
7-day eastbound 85th percentile speed = 37.6 mph
7-day westbound 85th percentile speed = 38.9 mph

* Figures from February 2013, supplied by Vale of Glamorgan Council following a Freedom Of Information request.

Figures from the Vale of Glamorgan Council - Freedom of Information request.

Research has found there is a link between road width, sight lines and speed - DfT, Manual for Streets. 

Annex B
Visibility Standards
B.1  The visibility provided along a link will affect the speed at which drivers choose to travel. Therefore the prevailing traffic speed can be influenced by the design of the environment. 

The official view of the Vale of Glamorgan Council can be found in the following minutes:

The Vale of Glamorgan Council  

Scrutiny Committee (Economy and Environment): 1st November 2011


Report of the Director of Environment and Economic Regeneration


Traffic Issues A48 St. Nicholas to Bonvilston

St. Nicholas

Speed data through St. Nicholas does not indicate that there is a significant problem with both average and 85th percentile speeds below the Association of Chief Police Officers (ACPO) prosecution levels.  No further action proposed.