Data Collection Issues

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Data Collection Issues

• Christopher R. Bennett

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Types of Data

• Inventory Data
• physical elements of road network that do not
  change markedly over time
• Condition Data
• elements of the road network that change over
  time
• Traffic Data

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Deciding What to Collect

• What decisions do we need to make?
• What data are required to make these decisions?
• Can we afford to collect the data initially?
• Can we afford to keep data current over time?

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Criteria for Selecting Data Items

• Relevance
• Appropriateness
• Reliability
• Affordability

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Relevance

• Every data item must have a direct influence on
  the system output
• Data relevance depends on the items ultimate use
  
• Data items which are considered to be desirable,
  interesting or possibly useful should be omitted

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Appropriateness

• Technology and resources used in acquiring,
  processing and managing the data should be
  appropriate to the administrations capacity for
  maintaining the equipment, conducting the surveys
  and processing the data
• Data collected to appropriate level of detail

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Appropriateness ...

• Frequency of data collection based on rate of
  change of item out-of-date data are often
  irrelevant
• Trade-offs need to be made between precise data
  collected infrequently on the one hand and less
  precise data collected more frequently

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Reliability

• Levels of accuracy and reliability vary
  considerably between different applications
• Data must be consistent over time and between
  locations
• The aim should be to have high levels of
  repeatability and reproducibility

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Precision vs Speed
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Affordability

• Size and quality of all data and their
  acquisition must be affordable in terms of cost
  and resources
• Scope of data collection weighed against
  resources required to sustain it
• Automated data collection not always more
  affordable than manual

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Guiding Principle

• Collect only the data you need!
• Collect it only when you need to!
• The level of detail should be appropriate for the
  decisions being made network level data for
  network level analyses project level for project
  level

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Information Quality Levels (IQL)

• Introduced by World Bank to help determine data
  requirements and design systems
• Recognises that different levels of data are
  needed for different levels of management
  activities
• Ensures that only enough data are collected to
  enable appropriate decisions to be made

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IQL
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Management Data Requirements
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Strategies for Data Collection

• Hierarchical
• IQL - IV across whole network
• IQL - III on sections likely to be programmed for
  work
• IQL - II on sections selected for design
• Cyclical
• IQL - II/III on part of network as rolling 3-5 yr
  programme

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Data vs Calibration
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VERY IMPORTANT DATA

• Average Annual Daily Traffic
• Traffic Growth Rate
• Hourly Distribution of Traffic
• Discount Rate

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RUE - Main Data

• Cost of Crew
• Cost of Maintenance Labour
• Cost of Petrol/Diesel
• Cost of Replacement Vehicle
• Cost of Travel Time
• Cost of Tyre
• Interest Rate
• Low Flow Interaction Level - Qo
• Nominal Capacity - Qnom
• Speed at Nominal Capacity
• Speed at Ultimate Capacity
• Ultimate Capacity - Qult

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RUE - Secondary Data

• Cost of Engine Oil
• Cost of Retreads
• Average Annual Utilisation
• Average Service Life
• Braking Power
• Depreciation Method
• Desired Speed
• Driving Power
• Equivalent Standard Axles
• Hourly Utilisation Ratio
• Hours Driven

• Number of Crew
• Number of Passengers
• Number of Wheels
• Operating Weight
• Percentage of Private Use
• Rated Power
• Tyre Type
• Utilisation Method
• Vehicle Equivalency Factors
• Volume of Wearable Rubber
• Wheel Diameter

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RUE - Unimportant Data

• Aerodynamic Drag Coefficient
• Cost of Cargo
• Cost of Overhead
• Drag Coefficient Multiplier
• Number of Axles
• Projected Frontal Area
• Travel on Snow Covered Roads
• Travel on Wet Roads

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Pavements - Important Data

• Capacity
• Structural Number
• Surface Type
• Unit Costs for Construction and Maintenance

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Pavements - Secondary Data

• Area Potholed
• Area with All Cracking
• Area with Wide Cracking
• Benkelman Beam Deflection
• Carriageway Width
• Construction Age
• Construction Fault
• Horizontal Curvature

• Maximum Acceleration Noise
• Number of Surface Layers
• Preventative Treatment Age
• Rise plus Fall
• Roughness
• Subgrade CBR
• Surfacing Age
• Thickness of Surface Layers

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Pavements - Unimportant Data

• Altitude
• Area of Previous All Cracks
• Area of Previous Wide Cracks
• Average Rainfall
• Base Type
• Cracking Retardation Time
• Effective Number of Lanes
• Mean Rut Depth
• Number of Base Layers

• Number of Rises and Falls
• Posted Speed Limit
• Ravelling Retardation Factor
• Sand Patch Texture Dept
• Shoulder Width
• Soil Cement Resilient Modulus
• Standard Deviation of Rut Depth
• Superelevation
• Thickness of Base Layers

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More on PCSE
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Equivalencies

• Used to convert heterogeneous stream to
  homogeneous stream
• Two types
• PCE Passenger Car Equivalencies
• PCSE Passenger Car Space Equivalencies

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PCU Calculation
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PCU Calculation Example

• Ideal capacity is 2000 PCU/h/lane
• Observed capacity 1600 veh/h with 80 passenger
  cars (1280) and 20 (320) heavy trucks
• Impact of trucks on flow
• 2000 PCU - 1280 PCU 720 PCU
• 720 PCU/320 trucks 2.25 PCU/truck

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PCSE Calculation
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PCSE Calculation Example