There are three key factors to be satisfied in our traffic estimation process, underpinned by a sound traffic count strategy. It is important to understand satisfactory confidence in our estimates and having this at the time they are made. Satisfactory confidence will vary for each link depending on its criticality and role within the network. This is important when we are considering inclusion of factors like seasonal correction or how growth is considered. For example, we require a higher level of satisfactory confidence in traffic estimates for our more important roads. We are less concerned about the accuracy of the estimates on our lower hierarchy roads. This manifests itself in less frequent sampling or count frequency on these sections.

Three key confidence areas are:

1. Achieving satisfactory confidence in total journeys on the network (vehicle kilometres travelled (VKT))
   1. The traffic count program, predominantly the core counts, cover the busier links with higher frequency to enable better sampling coverage in those links that carry more of the network journeys. The estimates, for the busier links particularly, therefore provide sufficient confidence that our VKT is representative of our network. The lower hierarchy links have less influence and therefore require less confidence.
2. Achieving satisfactory confidence in my AADT estimates for each link
   1. The (predominantly) rotational sites particularly spread the link counts across the network to give appropriate confidence in the estimate for links in each hierarchy. As the hierarchy typically decreases, links are less critical and are counted with less frequency. Typically, lower hierarchy links will have estimates with lower confidence levels. For example a low volume route, there is little impact if the estimate is say 20 or 30 vpd, a 50% difference. However a higher volume road will not tolerate an estimate difference of 2000 or 3000 vpd, the same 50% difference. Hence, we can estimate lower volume routes less frequently than higher volume routes as we are less concerned about the confidence in the estimate. This can be about how recent and/or how proximate the data was that we are calculating the estimate from. On higher volume routes, we will have more count sites along the road which are counted more regularly. Conversely, on lower volume routes we will have fewer count sites along the road and count them less frequently.
   2. There will be routes and links in lower hierarchy categories that we would like more confidence in understanding and estimating the AADT. Examples are quarry or forestry routes, routes with increased growth, seasonal factors, event tracking or transport planning such as cordon or screen line sites. Areas can include land use change or high growth.
3. Achieving satisfactory confidence in the type of vehicles on my road network (traffic mix)
   1. Both volume and traffic mix are important. Loading on pavement and tracking freight movements are important components in traffic monitoring. The estimation process should satisfactorily accommodate both volume and mix to both network and link level

A further factor is journey knowledge or how are the journeys being undertaken across our network. This issue is becoming increasingly important, particularly when we start considering place functions of different links. This issue is not discussed as part of this report as it reflects more on how we capture traffic data.