Modified simplification of HDM-4 methodology for the calculation of vehicle operating cost to incorporate terrain and expanded to all vehicle types for use in the Western Cape contextF HDM-4 METHODOLOGY FOR THE CALCULATION OF VEHICLE OPERATING COST TO INCORPORATE TERRAIN AND EXPANDED TO ALL VEHICLE TYPES FOR USE IN THE WESTERN CAPE CONTEXT

[摘要] ENGLISH ABSTRACT: INTRODUCTIONThe Western Cape Government (WCG) uses Vehicle Operating Cost (VOC) as part of their Road Management System since 1992. VOC is used in the process of prioritisation of maintenance projects as well as for the identification of economically viable maintenance strategies and is thus an integral part of the system.In 2001 changes to the VOC calculation methodology in the system to Highway Development and Management (HDM-4) system methodology occurred. The reasons were twofold – to bring the calculation method in line with world trends and due to lack of updated cost factors used in the previous methodology.In October 2001 a model was implemented with riding quality (IRI) as independent variable. This model was partly based on regression table data. As no geometric/topography data, defined as Terrain data, was available at this stage, Terrain was ignored. In 2006 WCG Systems were updated with Global Positioning System (GPS) data and a process to classify or categorise Terrain was initiated, thus providing the opportunity to include Terrain. As part of the redevelopment to include Terrain, it was decided to re-evaluate the vehicle fleet.METHODOLOGYVarious alternative methods to develop the Modified Simplification equations were available and evaluated, e.g. regression or direct mathematical substitution. HDM-4 requires the input of Vehicle Type dependent cost parameters that is based on realvehicles. The WCG required that changes to these dependent parameters isfeasible, so that they can be updated periodically. A set of equations thereforeneeded to be developed, allowing the input of Vehicle Type dependent parametersand the subsequent calculation of VOC with riding quality (IRI) as independentvariable. This renders the use of regression analysis untenable.Composition of the vehicle fleet on each road section is required to utilise HDM-4 foranalyses. In order to simplify calculations, different traffic strata was defined, i.e.Business, Commuter, Rural and General. In the evaluation of the Vehicle it is thisstrata and data from permanent counting stations that is used to compile a Vehiclefleet.MODEL DEVELOPMENTThe Modified Simplification to include Terrain results in 48 combinations of VehicleType, Surface Type and Terrain Type for the basic equation of VOC. VOC = TCav + PARTSCOST + LABOURCOST +DEPCSTav ( )´Length of road segment1000+(FuelCostav +OilCostav )´ Length of road segmentav TC -Tyre Cost PARTSCOST -Parts Cost LABOURCOST - Labour Costav DEPCST - Depreciation Cost av FuelCost -Fuel Cost av OilCost - Oil CostThe variables in VOC are defined by a couple of equations. For explanatorypurposes a numeric example is presented. CONCLUSION AND RECOMMENDATIONThe implementation of this Modified Simplification has assisted not only the WCG, but also other entities, that also use the VOC (published annually) based on these principles. Interested parties have the option to include Terrain in their implementation. Caution should be taken when using the Modified Simplification, as it is important that the principles used to simplify HDM-4 apply to the implementation and the business rules of the Management system of the user.The current development will not require a redevelopment due to any vehicle fleet change in future as the decision to simplify all defined Vehicle Types in HDM-4 allows the new fleet to be updated.Recommendation for further research and development include:• Standalone function that is already considered by the WCG• Investigating Published Vehicle data• Economic vehicle data for use in specific applications

[发布机构] Stellenbosch University