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TRAFFIC

This presentation provides an overview of traffic data input, traffic categories, representative vehicles, traffic composition, volumes and growth rates, axle loading, speed-flow type, and traffic flow patterns. It also explores the uses of traffic data in HDM-4, including pavement deterioration, vehicle operating costs, travel time, vehicle exhaust emissions, energy use calculation, and economic analysis.

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TRAFFIC

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  1. TRAFFIC Linda Parsley

  2. Overview of Presentation • Traffic data input • Traffic categories • Representative vehicles • Traffic composition • Traffic volumes and growth rates • Axle loading • Speed-flow type • Traffic flow pattern

  3. Uses of traffic data in HDM-4 • pavement deterioration • vehicle operating costs • travel time • quantities of vehicle exhaust emissions • calculation of energy use • economic analysis

  4. Location of input traffic data Definition of project details: • Road sections • Vehicle Fleet • Normal Traffic Specification of Alternatives: • Improvement standard Configuration

  5. Traffic Categories • Normal traffic • Existing traffic and expected growth on the road both with and without the investment • Diverted traffic • Traffic diverted to the road as a result of the investment • Generated traffic • New traffic induced by the investment

  6. Representative Vehicles • Purpose: • to group vehicles with similar characteristics to simplify input • Method of grouping: • composite vehicle - average characteristics of vehicles within the group • actual vehicle - actual characteristics of most common vehicle of the group

  7. Vehicle Hierachy Three levels: • Categories • motorised and non-motorised traffic; • Classes e.g. • passenger cars, trucks, buses, carts…. • Types e.g. • small car, medium car, large car, Toyota Corolla, Mercedes Benz…...

  8. Motorised traffic Category Class Type

  9. Non-Motorised traffic Category Class Type

  10. Volume, composition and growth rates • Volume - AADT for MT & NMT • Composition - representative vehicles (%) • Growth - for specified periods • Annual percentage increase % • Annual increment of AADT • Actual AADT for each section

  11. Axle loading For each representative vehicle • Number of axles • Equivalent standard axles • affects paved road deterioration • Number of light vehicles (< 3.5 tons) • affects deterioration of unsealed roads

  12. Traffic Interactions

  13. Traffic Interaction Modelling • HDM-III did not consider traffic interactions • HDM-95 considered effects of traffic interactions on speeds but not on other VOC (fuel but only through speed reduction) • HDM-4 expanded the HDM-95 approach to consider other VOC components

  14. Traffic interactions • Passenger car space equivalence • Speed flow types • Traffic flow patterns

  15. Equivalencies • Used to convert heterogeneous stream to equivalent homogeneous stream • Two types • PCE/PCU: Passenger Car Equivalencies • PCSE: Passenger Car Space Equivalencies • HDM-4 uses PCSE

  16. Differences between PCU and PCSE • PCU/PCE • consider two factors: • space occupied by vehicle • speed effects • used in highway capacity calculations • PCSE (HDM-4) • considers only space occupied • speed effects considered separately through speed model

  17. PCSE Gap Length Space (m)

  18. HDM-4 Speed-Flow Model

  19. Speed-flow model requirements • Requires speeds • Free speed (calculated) • Snom - Speed at nominal capacity (calculated) • Sult - Speed at ultimate capacity • Requires capacities • Q0 - Volume where interactions affect speeds • Qnom - Nominal capacity • Qult - Ultimate capacity specified in Configuration

  20. Types of Capacities • Nominal Capacity • the capacity where the traffic stream is travelling at a constant speed • sustainable over long time periods • Ultimate Capacity • maximum possible capacity before flow breaks down

  21. Annual Distribution of Hourly Flows Flow Periods Peak Next to Peak Medium flow Next to Low Overnight Number of Hours in the Year Flow /hr

  22. Non-Motorised Traffic

  23. Impact of NMT • NMT affect • Motorised traffic flow and speed • Motorised traffic operating costs Impact is specified through a friction factor • NMT also affect • Safety related costs • Road maintenance costs these are not considered in HDM-4

  24. Other effects on speeds • Impact of roadside activities - side friction • Impact of road widths as limiting speeds • Speed limits • Enforcement factor

  25. Key differences from previous models • Unlimited number of representative vehicles • Effects of congestion on speed, fuel, tyres and maintenance costs • Non-motorised transport modelling

  26. Location of input traffic data Definition of project details: • Road sections • AADT, speed factors, speed-flow type, traffic-flow type • Vehicle Fleet • axle loads, PCSE, speed parameters • Normal Traffic • composition, growth rates

  27. Location of input traffic data Specification of Alternatives: • Improvement standard • Diverted traffic / generated traffic Configuration • speed flow types, traffic flow patterns

  28. Summary • Aimed to show where traffic data is required in HDM-4 and its relevance and impact in the model • Included traffic interaction and speed estimation which leads to VOC and RUE

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