SCANNER quality assurance and audit-Auditor's QA

Auditor's QA


The Auditor monitors the contractor’s internal QA processes to ensure these are of suitable quality and are correctly implemented. The auditor also undertakes a QA programme to ensure the collected SCANNER data is of the best quality. The QA programme consists of independent checks of the contractor’s monthly primary site surveys, a quality audit of all the network data collected by the contractor, and the option to carry out repeat surveys using their reference device on a selective sample basis.

SCANNER Quality Audit of Network Data

The SCANNER quality audit is carried out by comparing the SCANNER data provided in the current SCANNER survey year with that collected in the previous year. The objective is to confirm the consistency between the measurements collected in the two years.

The SCANNER data for the current year is provided to the Auditor by the survey contractor within a few weeks of the completion of processing the data. The Auditor collates and stores the data for each year, and therefore already holds the data obtained in the previous survey year. The Auditor assesses whether the current data is consistent with the previous data by obtaining statistics on the current and previous data, including

* The mean value for each SCANNER parameter

* The frequency distribution of each SCANNER parameter

* The percentage length of each SCANNER parameter falling within the red amber and green categories defined by the RCI threshold

* The percentage of the network for which the RCI exceeded 100 for all road types. This is not the same as the Data Topic 130, it is called the “SCANNER Audit Indicator”.

The statistics are assessed against performance criteria derived from the consistency that would be expected to be observed between the SCANNER vehicle(s) that carried out the surveys in the current survey year and the SCANNER vehicle(s) that carried out the surveys in the previous survey year. These performance criteria are established during the SCANNER vehicle accreditation tests and are reviewed annually.

The performance of the statistics against each criteria are used to award an Auditor’s Overall Assessment. If the Auditor is happy with the performance an assessment of “Satisfactory” is awarded. If the Auditor is not satisfied with some of the differences seen an assessment of “Further Investigation Recommended” is awarded and the contractor is asked to investigate the reason for the changes being seen. If more severe differences are seen the Auditor can award an assessment of “Re-survey Required” and will request that the contractor repeats the affected surveys.


Auditor's repeat surveys

These demonstrate the reproducibility of the SCANNER survey equipment. The procedures for these tests are:

* The auditor selects and repeats a SCANNER survey using an independent survey vehicle.

* Each repeat survey will have an individual length of no more than 10km.

* The contractor supplies the SCANNER data from this survey to the auditor.

The auditor will compare the two data sets to see if the assessment has been successful and if any further action is required.

Enquiries about SCANNER quality assurance process should be addressed to either Alex Wright, Patrick Werro, or Chris Torkington of TRL, or alternatively email

TRL Crowthorne House Nine Mile Ride Wokingham Berkshire RG40 3GA Tel: 01344 773131 Fax: 01344 770356