Links are carriageway sections with similar traffic characteristics of volume and mix. Links effectively reduce the total number of sections for potential count sites across the network. This increases the effectiveness of our count programme by making it an increased proportion of our network sections. We have included guidance on creating links.

There are three types of links we must be considering in how we update our estimates.

• Links counted recently
  • Counts undertaken recently on a link are obviously the best source of information for updating an estimate for that link. Consideration is therefore needed as to what is an appropriate process to turn that moment in time record to a representative annual traffic estimate.
  • Consideration is to what is recent enough to be used. Recent may vary from last year or even multiple counts in a year on a higher-level road to say three years ago on a lower level road to achieve or sustain the required level of confidence
  • Time should also be a factor so looking at trends from past counts. Again, this is easier on more frequently counted sites
  • The balance is around adequate confidence in the number or age of “recent” counts such that the link still falls into this category or it needs to use alternative methods detailed in the other two link estimation processes detailed below.
• Links adjacent enough to be directly influenced by recent counts
  • Once we have estimates for sites we have counted recently, we can then assess links that are directly affected. This can vary from links on a road next to a counted link or between counted links. Great South Road for example will have many counted links and estimates for the remaining links can be determined from interpolation.
  • Methods can vary from using automated methods that are then sanity checked to the parent/child method where all child links fall under this category.
• Links with no recent or adjacent count
  • Effectively estimates are initialised and updated based around similar link sections or assumptions. Some, on long term rotational programmes, will be reset when a count is undertaken. But other links may never be counted. So, an appropriate methodology reflecting the required confidence in the estimate is required.

When we are considering updating estimates, we therefore need to be cognisant of answering the first three questions for each of the three types of links.