AP-G84/04 Best practice in road use data collection, analysis ... - WIM

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Accessed by AR - ARRB TRANSPORT RESEARCH on 04 Feb 2005 Austroads 2004 — 40 — Best Practices in Road Use Data Collection, Analysis and Reporting 6.2 Specifications for Data Collection Activities It is recommended that specifications for data collection activities be developed irrespective of whether the survey is undertaken by in-house staff or contractors. These specifications can be used to ensure consistency in data collection and provide a basis for assessing data quality. Surveys undertaken by third parties define the work by means of a brief. It is recommended that a modified version of the brief be used for surveys undertaken by in-house staff. GTEP Part 3 states that the following points must be included in a brief: General outline of type of survey to be undertaken and purpose; Details of field survey and survey design (if included) required; Competencies required and field instruction detailed; Criteria for data acceptance; Structure of data outcomes; and Provision of method for conducting survey, data quality plan and training proposed by consultants. Tenders should then be assessed on the basis of management capability (scheduling, contingency planning, staff recruitment and training, quality plan, resource programming), technical capabilities (project management skills of key personnel and level of technical support), price and documented prior experience. The key to successful data collection lies in the attention paid by the study manager to the details of survey administration. The following checklist may help to reduce the severity of problems arising during a traffic study. The checklist is particularly suitable for the manual collection of data, but the principles are suitable for the collection of most road use data. (a) Personnel must receive training in the purpose of the survey and in the methods of measurements to be employed. (b) Replacement field staff should be available, especially on the first day of a multi-day survey. During the survey, rosters of rest periods for observers are essential, and replacement staff will be needed to cover these periods. (c) Survey forms should be prepared and distributed, as far as possible, on the eve of the survey. The pre-study briefing is ideal for this distribution. (d) Procedures should be in place for early checking of data quality and for consequential modifications to the survey operations to be made. Plans and procedures should be in place to accommodate failure to obtain information. (e) Occupational health and safety policies must be followed. Rest and meal breaks must comply with relevant industrial awards. These are essential in maintaining the alertness and concentration of field personnel and reducing the errors of observation and recording. (f) Privacy legislation must be followed. Data of confidential nature should not be disclosed without proper clearance. Transit New Zealand has out-sourced the collection of traffic data for a number of years. It has 89 Pattern Stations and 1,400 Short-term Stations. A single contractor provides the service of collecting data from the Pattern Stations which are all telemetry sites throughout New Zealand. Several independent contractors collect data from the Short-term Stations. The specifications provided to these contractors follow the principles outlined above and represent a set of best practice specifications (Transit New Zealand 2002). The following two procedures adopted by Transit New Zealand are of interest in data quality control: (a) Data validation against independent means – the contractor specifications include a traffic counter operational check. The contractor is to fax the form to Transit New Zealand within 48
Accessed by AR - ARRB TRANSPORT RESEARCH on 04 Feb 2005 Austroads 2004 — 41 — Best Practices in Road Use Data Collection, Analysis and Reporting hours of the counter being installed in the field. This allows Transit to undertake independent visual surveys at random to ensure the contractor is performing as expected and providing quality data. Any variation between recorded data and the visual surveys of ± 5% will result in the contractor having to repeat the survey at their cost. (b) Cross-checks - The contractors responsible for the Short-term Stations are asked to undertake random (once very three years) classified counts at each of the permanent telemetry sites as a way of independently validating the accuracy of each other’s equipment and data collected. Any variance of ± 5% is then the source of investigation to assess why the results are different. As both parties are independent, the contractors have a strong incentive to ensure their methodology and equipment accurately record traffic at these sites. In summary, the counting personnel whether contractors or in-house staff should be well prepared in terms of counting equipment, suitable seats, appropriate clothing including contingency provisions for adverse weather, amenities (food, toilet), and carry authority certificates. Conspicuous signage is not recommended as it may affect count results. 6.3 Quality Check and Dealing with Missing Data The principle of editing data and identifying missing data is endorsed as a good practice at the October 2003 Road Use Data Workshop. The Department of Infrastructure, Energy and Resources in Tasmania recommended the need to describe clearly how the editing is carried out. This may involve the use of metadata to provide traceability (metadata is ‘data on data’ used to describe the content, condition and other characteristics in the data). In US, Smith et al. (2003) endorsed a similar principle and suggested the need to reconsider the AASHTO (1992) policy of not estimating missing (or ‘imputing’) data. Each RA has its own data quality checking procedures, which are also different for different data types. It is beyond the scope of this report to record all procedures; however, few examples of current practices from Queensland Main Roads, RTA NSW, Main Roads WA and the CSIRO software developed for RTA, are presented below for illustration. The current Queensland Main Roads practice is to ensure complete data sets at Pattern Stations during annual processing. Missing data are computed at the hourly level using weekly and hourly adjustment factors, i.e. Missing hour volume = Anticipated AADT × Week factor × Hour factor RTA NSW pays special attention to classified counts and the data rejection rules for classified counts at RTA NSW are shown in Table 17.
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AP-G84/04 Best practice in road use data collection, analysis ... - WIM

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