An index is a statistical measure of changes in a representative group of individual data points over a time period. The TII Traffic Indices represent a measure of global traffic demand over time for a particular grouping of traffic monitoring units (TMUs) on the National Roads Network.
TII Traffic Indices for all traffic and HGVs only are available nationally, by region, by road type, by TEN-T network status and for certain corridors of interest. This allows for broad estimates in traffic growth trends on a national or regional basis and on the basis of road type, route corridor and vehicle type.
The traffic indices are produced on a quarterly basis and annual growth rates can also be output. The base for the TII Traffic Indices is Q3 2013.