SCANNER for Local RoadsImplementation Advisory Group20 May 2005

TA/MTRC 15.2Progress Note 6HALCROW

SCANNER for local roads – Implementation Advisory Group

Progress Note 6

TTS Surveys in 2004/05, SCANNER Surveys for 2005/06

Introduction

This note reports:

  • Progress of TTS surveys on Principal Roads in 2004/05
  • Reporting BVPI(96) on Principal Roads in 2004/05
  • Issues raised by QA and Audit testing in 2004/05
  • Specification for SCANNER surveys in 2005/06
  • Accreditation of vehicles for SCANNER surveys in 2005/06
  • BVPI survey requirements for 2005/06
  • Developing a new SCANNER Road Condition Indicator (Defects Index)
  • Recommended SCANNER survey requirements for 2006/07
  • Preparations for SCANNER surveys in 2007/08

Progress of TTS surveys on Principal Roads in 2004/05

Three survey machines eventually passed the acceptance tests for accreditation to the current TTS specification. These are WDM's Road Assessment Vehicles RAV2, accredited 16th April 2004 and RAV3 accredited 13th July 2004 and Jacobs Babtie's RST Laser vehicle, accredited to perform surveys 19th May 2004, accredited to deliver post processed survey data 4th August 2004.

DCL submitted a Roadware ARANfor testing in January 2005 and it has carried out the site and network tests. A number of technical details are still being investigated.

After a disappointingly slow start to the TTS surveys at the beginning of the year both WDM and Jacobs Babtie made strenuous efforts to complete all their planned survey contracts. Jacobs Babtie reported survey completion on 28th March, with more than half of the survey data delivered to local authorities. WDM reported survey completion on 31st March with more than 80% of the survey data delivered to local authorities.

Although DCL has not yet received accreditation, it also carried out some surveying before 31st March for local authorities, at its own risk, after completing the accreditation test surveys.

In total, more than 48,000 lane km of road was surveyed. This may be compared with the length of principal roads in England (24,570 km) and TRL's estimate of the length to be surveyed in 2004/05 (53,997 lane km). In total, 90% of the English principal road network was surveyed by one or other TTS accredited survey machine in 2004/05.

Reporting BVPI (96) on Principal Roads in 2004/05

Some local authorities will not have valid survey results to be able to report BVPI(96) for 2004/05 in June 2005. The DfT raised this issue with the Office of the Deputy Prime Minister and the Audit Commission, which has agreed that BV(96) will not form part of the Comprehensive Performance Assessment (CPA) and:

a)Where the survey company has been able to survey in excess of 85% of the principal network, the authority may deem the results from that coverage to be the PI, and

b)Where the local authority has not been able to procure even 85%, they will not be required to submit a BV(96) figure. In this case, provided that the authority can show that it had taken adequate steps to procure the surveys, the PI results will not be qualified.

Many local authorities have experienced a significant increase in the BV(96) result. The DfT investigated the possibility of amending the BVPI specification to exclude texture measurements, but was advised by the Road Liaison Group not to change the requirements. The chairman of the UK Roads Board, Matthew Lugg, wrote to local highway authority chief executives on 9th May and a copy of his letter is attached at Annex A. The CCS circulated a copy of the letter to members on 6th May and the TAG has also circulated a copy to members.

Issues raised by QA and Audit testing in 2004/05

As part of the introduction of TTS on principal roads in 2004/05, the DfT placed a contract with TRL Limited to provide a limited quality assurance and audit service to all English local highway authorities. This provided an independent audit of the survey operator's own QA procedures, which are set out in the TTS specification, and a number of independent repeat surveys on a limited sample of local authority roads.

Most aspects of the surveys were satisfactory. A detailed report is being prepared and a summary report was presented at the TTS IAG on 23rd March 2005 by TRL. TRL identified four main areas of concern that will require further attention and improvement in 2005/06:

Location referencing and network definitions. Contractors are subject to a significant burden of dealing with poorly referencednetworks e.g.; incorrect section lengths; lack of section start and end points making route planning difficult; section directions defined incorrectly; sections added to the network but the definition not updated. Poor definitions affect location referencing and audit. Local authorities should make a greater effort to provide correct network definition data, as this is not the Contractor’s responsibility. Poor network definitions adversely affect BVPI accuracy and relevance by stretching and shrinking data. It may be difficult to correct network definitions using TTS data if the data has already been stretched or shrunk to fit the ‘incorrect’ network.

Quality (not accuracy) of delivered data. The quality of delivered data often caused difficulties for local authorities. Mistakes such as; omissions; start chainage greater than end chainage; negative chainage. Survey contractors should make a greater effort to ensure the quality of data delivered to minimise the time wasted by local authorities in accepting and processing the data.

There are issues with the range of survey data. For example, there are inconsistent methods of rounding chainage to the nearest metre. There are questions about what range of parameter values is valid and what should be done with data exceeding these ranges? Is it sufficient to set it to the range limit or is the magnitude important? Who should deal with these extreme values? These issues will be investigated and resolved as part of the SCANNER implementation project.

Compatibility of delivered data. Compatibility issues were identified with various UKPMS systems. Should the survey contractor be responsible for such problems? Should the UKPMS standard be defined more rigorously? There is a need for action on both sides, survey contractors and UKPMS developers. The UKPMS support consultant is taking these issues up with the industry.

Accuracy of measurement of cracking. Crack detection is a “new” parameter and it has become subject to suspicion. Repeat surveys show this measure is repeatable – more so than typical visual surveys. Comparisons between auditor's and survey contractor's data show agreement over significant lengths but with significant localised differences. Development is needed for the user to have the same confidence in the measurement of cracking as the other parameters. Possible improvements include: surface type adjustment; identifying and eliminating white lines, cats-eyes and out of lane features. This will be taken forward as part of the TRL research on cracking.

Specification for SCANNER surveys in 2005/06

The Roads Board has adopted the name SCANNER (Surface Condition Assessment for the National NEtwork of Roads) for the new specification and surveys to commence in 2005/06.

A revised specification has been drafted for SCANNER surveys, based extensively on the current TTS specification. The main changes are in the layout of the documents, it now consists of five separate, but linked, documents:

  • Advice for local authorities including a glossary of terms and a model contract document;
  • Specification for services, including details of survey procedures, data processing, route fitting and calculation of derived parameters
  • Acceptance testing and Accreditation
  • Quality Assurance and Audit
  • Further technical guidance.

The draft specification was issued for comment in December 2004, and extensive comments were received from the survey operators, from the UKPMS system developers and support consultant, from local authority representatives and from TRL as the Acceptance and QA tester and as the Auditor.

The specification was amended to reflect these comments and was issued in March 2005 as a basis for moving forward into 2005/06, and for further comment. Further comments were received and the draft specification was discussed at a number of meetings. A further revision is being completed at present and it will be re-issued within the month.

There are still some outstanding issues to be resolved, including the development of the Machine Survey Pre-processor (MSP), which was originally developed by the Highways Agency and is used by some survey companies to process survey data from a "Raw Condition Data" format to a UKPMS HMDIF file. The main developments required include fitting SCANNER survey data to the route file in a standardised way and enabling MSP to produce new transverse profile and edge deterioration parameters from the transverse profiles collected by TTS / SCANNER vehicles.

Accreditation of vehicles for 2005/06 SCANNER Surveys

The DfT has awarded a new Accreditation, QA and Audit testing contract to TRL Limited from 31st March 2005 until at least September 2007. Following discussion with the survey industry and TRL, it has been agreed that the Accreditation certificates should cover a period of up to 15 months, but be renewed at yearly intervals, to enable machines to operate continuously with a valid certificate.

TRL has made arrangements for re-accreditation testing of the machines currently accredited to the TTS specification. Because the technical requirements for BVPI reporting in 2005/06 can be met by machines accredited to either the TTS or SCANNER specifications, the survey operators with accredited machines are able to continue surveying without delay.

BVPI survey requirements for 2005/06

The ODPM has announced new BVPI numbers for the condition of local roads: BV (223) replacing BV(96) for principal roads and BV (224)a replacing BV(97)a for other classified roads. This is to emphasise that the new road condition performance indicators measured by SCANNER are qualitatively and quantitative different from those measured by previous methods, such as Deflectograph and CVI.

In November 2004, the Roads Board confirmed their recommendation for the MINIMUMsurvey requirements for 2005/06, taking account of the number of survey machines likely to be accredited and available during the year.

  • Completion of full surveys on principal roads which were not surveyed in 2004/05, in both directions. (Currently estimated to be some 6,000 lane km in total).
  • Where an authority has substantially completed (over 85%) the principal road survey in 2004/05, it should resurvey at least half the principal road network, eitherthe whole length in one direction or half the length in both directions. (Potentially some 24,250 lane km).
  • Local authorities should survey all B roads in one direction only. (Potentially some 20,000 lane km)
  • Local authorities should survey a representative sample of at least 10% of C roads in one direction only, with a minimum survey length of 50 lane km per local authority (where possible). (Potentially some 6,500 lane km plus 3,000 lane km to meet the minimum length requirement.).

This gives a minimum total survey requirement for at least 60,000 lane km in 2005/06, much of it on smaller roads where survey productivity is likely to be lower.

The Roads Board also considered the requirements for surveying de-trunked roads and principal motorways and has recommended that they be included in the surveys, with the objective of achieving enough coverage to provide results from two surveys, in both directions, by March 2007.

Where the total length of C roads is equal to or less than 50 km, the whole length should be surveyed in one direction only.

The sample of C roads to be included in the survey will not be random but it should be broadly representative of each authority's network and chosen for operational convenience. It may be appropriate to discuss the selection of the sample with the survey contractor, taking account of factors such as linking survey routes on A and B roads and selecting larger C roads that may be more suitable for SCANNER surveys.

Where the authority has built up and non-built up areas, the sample should be chosen to reflect the proportional length of C road in built up and non-built up areas. Where the authority covers a wide geographical area, the sample should be chosen to include sections from the different parts of the authority, broadly in proportion with the length of C road in those parts. Where the authority covers different topographies – for example lowland and upland areas – the sample should be chosen to include sections from the different topographies, broadly in proportion with the length of C road in those areas.

Guidance on how to combine the results from surveys on B and C roads to report BV(224)a is currently being developed.

Guidance on how the BVPI is to be calculated from the SCANNER data is being developed, as described below.

Developing a new SCANNER Road Condition Indicator (Defects Index)

The Roads Board agreed to set up a joint working group of the Road Performance Management Group (RPMG), the SCANNER Project Management Group (PMG) and the UKPMS Steering Group in November with DfT, SRMCS and SCOTS representatives.

The Group met in December 2004, March and May 2005. Reports from the Group have been considered by the SCANNER IAG in March, by RPMG; SCANNER PMG and UKPMS SG in January and April, by SCOTS / SRMCS in February and by the Roads Board in February and May.

The Group has recommended a three stage approach to a new condition indicator based on the approach proposed by the Chris Britton Consultancy Limited (CBC).

In the first stage the Group accepts the CBC proposal for two thresholds for each parameter measured over a 10 metre subsection length:

  • A lower and an upper threshold, with zero score below the lower threshold and a fixed score of 100 above the upper threshold. Initial values for the thresholds were proposed but these need to be confirmed as part of the proposed pilot testing.
  • Non linear weighting for all parameters between the thresholds, based on the approach adopted in Kent, giving a proportionally higher score as the parameter nears the upper threshold. The precise shape of the relationship will need to be developed as part of the proposed pilot testing.

In the second stage the Group recommends an alternative to the three CBC proposals for combining the scores:

  • Reducing the score for each parameter by two factors;
  • one reflecting the relevance or importance of the measured parameter as an indicator of a defect and
  • another reflecting the level of confidence in the reliability of the measurement.
  • Combining the various parameters in "family groups" and only taking the highest scoring defect from each group.
  • Totalling the scores, rather than averaging them.

In the third stage the Group recommends one of the methods proposed by CBC for combining the scores from each sub-section for a section, area or network, using thresholds:

  • "Red": Total score over 100, lengths likely to need planned maintenance soon.
  • "Amber": Total score above 0 and below 100, lengths likely to need to be investigated further and considered for planned maintenance.
  • "Green": Zero total score, lengths likely to be in overall acceptable condition and not requiring any further investigation.

The consequence of this approach and the proposed thresholds, weightings and method of combining the scores is that no individual parameter would be sufficient to put a 10m subsection length into the "overall red" band. However any parameter scoring above the lower threshold would be sufficient to put a 10m subsection length into the "overall amber" band.

The Group anticipated that the percentage length of a network scoring "overall red" is likely to be quite small, whereas the percentage length scoring "overall amber" is likely to be quite high.

The Roads Board accepted the overall approach proposed by the Group, that the value being calculated should be called the (SCANNER) Road Condition Indicator and the values proposed for the thresholds and weightings should be tested against TTS data gathered on principal roads in 2004/05.

Recommended SCANNER survey requirements for 2006/07

In May 2005, the Roads Board re-considered the survey requirements for 2006/07 and confirmed its recommendation for the MINIMUM survey requirements for 2006/07:

  • Where an authority had not substantially completed (over 85%) the principal road survey in 2004/05, repeat the full survey in both directions. (Potentially some 6,000 lane km).
  • Where an authority had substantially completed (over 85%) the principal road survey in 2004/05, it should re-survey at least the part of the principal road network that was not re-surveyed in 2005/06, either the whole length in one direction or half the length in both directions. (Potentially some 24,250 lane km).
  • Local authorities should repeat the 2005/06 survey of all B roads in one direction only. (Potentially some 20,000 lane km)
  • Local authorities should survey at least 50% of C roads in one direction only, with a minimum survey length of 50 lane km per local authority (where possible). (Potentially some 32,000 lane km plus 1,500 lane km to meet the minimum length requirement.).

This would give a minimum survey requirement for about 83,500 lane km in 2006/07, much of it on smaller roads where survey productivity is likely to be lower.