Impact on the Local Network

When a development is proposed, the impact on the local highway network must be considered. The number and type of junctions to be assessed will depend on the location of the site. If the site is within a dense urban area then there will be more junctions to assess compared to a site in a quiet rural location. If the development is small with only a minimal increase in vehicular or pedestrian activity then it may not be necessary to undertake detailed capacity assessments of nearby junctions.

Type and Size of Development

The nature and size of a development will further determine the scope of junctions to be assessed. Junctions are assessed not only for the impact of additional traffic but also the impact of additional pedestrian or cyclist movements.  For example a large factory development may lead to a substantial increase in both vehicular and pedestrian movements but often, due to the shift patterns used, the impact will not be at the same time as the traditional highway network peak, a retail development on the other hand will lead to an increase in both vehicular and pedestrian movements during the traditional highway network peak hours.

The potential generated traffic for a development can be calculated by various methods.  These include grossing up existing traffic generations for a site if the proposal is for an intensification of use, or by using TRICS, a database of almost 6,000 traffic counts from various sites over the whole of the United Kingdom. By selecting a number of parameters a trip rate is produced for the selected type of development which can then be used to calculate the anticipated trip generation based on the floor area of the proposed development. Further details regarding traffic generations can be found at

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Impact on the Local Highway Network, Number and Type of JunctionsDetailed Assessments of Nearby Junctions Scope of Junctions