The use of groups is common in undertaking the creation and update of estimates. There are three main aspects where groups are used:

• Identifying carriageway sections and links that are tied to seasonal correction profiles. These profiles are used to allow for the variation of count volumes through the year when trying to ascertain an overall AADT estimate.
• Grouping carriageway sections and links with similar growth characteristics to enable sections with a count history to be extrapolated to update estimates on sections lacking in sufficient count history.
• Grouping carriageway sections and links with similar traffic mix characteristics to enable sections with a count history to be extrapolated to update traffic mixes on sections lacking in sufficient count data.

For the purpose of these guidelines, we have simplified these into two identified groupings with a consistent terminology:

• Road Type – for use in grouping sections and links against seasonal profiles. This group can include a default grouping where no adjustment is made.
• Traffic Group – for use in grouping sections and links with similar growth and traffic mix patterns.

These groups are discussed in more detail in Section 5 (Step 3 around the setting up of groups.).