Sections without Estimates

Before starting the process, checks should be made that each carriageway section has an estimate. Each section requires an estimate so that it can be incorporated into the process outlined in the guideline. These should be manually confirmed but there are various methods to establish an initial count such as looking at an average of the ONRC band the road is classified in to. Secondly, consideration should be made of changes to the network and whether localised links or estimates should be updated. Changes in traffic flows or new road infrastructure such as bypasses, attraction facilities or land use change should trigger review.

Process is as follows:

• Check RAMM Carriageway Table for any sections without a traffic estimate
  • Note – we are looking for those with no estimate only, not those with old estimates as we update them later in the process
  • Typically these will be generated from:
    • new carriageway sections added to the database as new roads vested to the RCA
    • new carriageway sections generated from existing carriageway sections being split. The estimate is linked to the carriageway start so creating a new carriageway section creates a new carriageway start.

A standard query report exists within RAMM to list sections with no traffic estimate. It is found under RAMM Manager Projects/Traffic Counting/Carriageways with no traffic estimate.

Carriageway Sections on new roads will typically require an estimate set manually by the asset manager. This will entail both an estimate of volume and traffic mix. For low volume roads, volume can be assessed based on a number of trips per household or looking at similar road sections on the network, preferably with a count record. Where new roads have feeder roads generating traffic will require a more planned approach to estimating traffic usage. Where an ONRC category has been set, an average volume maybe used or looking at similar road sections elsewhere on the network. Traffic mix can be estimated by other section on the same road that have count data or by using the average traffic mix from the traffic group assigned to the carriageway section.

For carriageway sections that have been created through changes to the network such as carriageway splits, it is important to understand the reason for the split. For these existing road sections, the adjacent sections can be used as a basis for setting an estimate. But the reason for the split is important as if it is to incorporate network changes that would impact flows then these changes need to be assessed. These need to be assessed on both the section without an estimate as well as those changes that may affect sections with estimates that need adjustment.

It should be noted to that where estimates are related to estimates nearby, they should be linked to the date of the relevant estimate rather than the current date.

Sections with network changes since the last estimate

This stage is a good point to look at the network and identify network changes or improvements that will have impacted flows significantly on any sections since the last estimate but where no count has been undertaken since. These may include sections impacted by new transport links, bypasses or new subdivisions. Other changes could be significant new trip generators such as new schools or event centres for example.

The revised estimate should be calculated and added manually into the data. It is important to note that this will be a starting point. If the carriageway section is on a key route, it is likely a count or adjacent count will be scheduled soon from which the new estimate can be revised. The estimate could be derived from experience, similar routes or the volumes used in the business case, planning or design processes.