The Highway Design and Maintenance Standards Model (HDM-III), developed by the World Bank, has been used for over two decades to combine technical and economic appraisal of road investment projects, standards and strategies. The International Study of Highway Development and Management (ISOHDM) has extended the scope of the HDM-III model to provide a harmonised systems approach to road management, with adaptable and user-friendly software tools. The new Highway Development and Management (HDM-4) system is the result of the study.

The new HDM-4 provides a powerful system for:

road management

programming road works

estimating funding requirements

budget allocations

predicting road network performance

project appraisal

policy impact studies

a wide range of special applications

The development of HDM-4 was sponsored by the leading international funding institutions and supported by national governments, and other organisations, particularly:

There are four main areas of application:

Strategic Planning

Roadwork Programming

Project Analysis

Research and Policy Studies

This application is used for strategic planning to prepare medium to long term planning estimates of funding needs for road network development and maintenance. The road network is characterised by lengths of road in different categories defined by parameters such as road class, surface type, pavement condition, traffic loading, etc. The main output are estimates of medium to long term budget requirements for the entire road system together with forecasts of pavement performance and road user effects.

This application can be used to prepare rolling work programmes in which candidate road sections are identified and assigned maintenance or improvement options. HDM-4 calculates the NPV and expenditure requirements of each option. The main output from Programme analysis is a schedule of optimum pavement maintenance and/or road improvement projects which can be carried out within specified budget constraints.

This project level application is concerned with the evaluation of one or more road projects or investment options. Road sections with user-specified treatments are analysed over a specified life cycle. Project analysis can be used to estimate the economic or engineering viability of road investment projects by performing life cycle analysis of pavement performance, maintenance and/or improvement effects together with estimates of road user costs. The main outputs include:

Annual predictions of pavement performance

Pavement maintenance and road improvement effects

Road user costs and benefits

Estimates of environmental effects

Standard economic indicators; NPV, EIRR, BCR, etc.

Typical projects include pavement maintenance and rehabilitation, road widening or geometric improvements, new construction, etc.

HDM-4 can be used to conduct a number of road sector policy studies including:

Funding policies for competing needs, e.g. feeder versus main roads

Road user charges for setting up Road Funds

Impacts of road transport policy changes on energy consumption

Impact of axle load limits

Pavement maintenance and rehabilitation standards

The HDM-4 database provides basic facilities for storing road network characteristics within HDM-4. Users can define several road networks and sub-networks, with an unlimited number of pavement sections. The HDM-4 network referencing system supports the concept of 'links' and 'nodes'. This approach to network referencing is designed to be flexible in order to integrate with a wide range of referencing conventions used in other databases with which HDM-4 may need to interface.

The HDM-4 database also provides facilities for storing characteristics of vehicle types required for calculating vehicle speeds, operating costs, travel time and other vehicle effects. Several vehicle fleets can be set up for use in different analyses based on the wide range of default data provided.

The HDM-4 configuration module can be used to customise all components of the system. Default data and calibration coefficients can be user defined for any country or region.

Any of the HDM-4 libraries/modules may be integrated with existing pavement management systems. Data import and export functions built into HDM-4 applications can be used to exchange data with external databases using standard data transfer specifications including ODBC.

The HDM-4 system is designed with a modular structure thereby permitting its total or selected integration with Pavement Management Systems (PMS). Any of the three application modules can be incorporated within a PMS. In addition, the technical relationships built into HDM-4 are contained within Windows libraries which can be linked into existing PMS so that a common set of pavement deterioration and road user cost models can be incorporated in other PMS.

The HDM-4 system includes a number of new or improved technical relationships:

Includes all three pavement surface classes:- unsealed, sealed/bituminous and rigid concrete

Wide range of pavement structural and surface defects

Routine maintenance

Periodic maintenance; e.g., resealing, resurfacing, overlays and pavement reconstruction

Development; includes widening, realignment and construction of new road sections

Delays and VOC at roadworks

16 representative vehicles have been incorporated based on results of recent research from which users can define an unlimited number

Vehicle speed models calculated under free-flow and congested traffic flow conditions

Improved models for fuel consumption, tyre wear, utilisation, spare parts, maintenance labour and vehicle depreciation

Calculation of diverted and generated traffic benefits

Calculation of travel time-savings for passengers and transit goods

Accident costs can be included within the economic analysis framework using specified accident rates and costs for different accident severity

Energy consumption models have been incorporated for estimating the total life cycle energy consumption, in terms of national and global energy sources

Vehicle emission relationships have been incorporated for estimating quantities of particulates, hydrocarbons and noxious gases

Non-motorised transport (NMT) effects and operating costs models are included

A separate set of stand-alone software is provided to help calibrate the following:

Detailed calibration of traffic congestion effects

Estimating delays and the additional VOC due to road works

Calibrating spare parts consumption

Estimating the optimal life of vehicles

Calibration of pavement deterioration rates

8 volumes of user documentation:

1. Overview of HDM-4
   A short executive summary describing the HDM-4 system
2. Technical User Guide
   Description of the analytical framework and the technical relationships
3. Software User Guide
   Description of the HDM-4 software
4. Applications Guide
   Typical examples of use of HDM-4 for various types of analyses
5. Calibration Guide
   Methods for data collection and calibration of HDM-4 in different countries
6. Road Deterioration and Works Effects
   Detailed description of the pavement deterioration and works effects relationships
7. Road User Effects
   Detailed description of models for VOC, speeds, accidents, NMT, emissions and energy consumption
8. Programmers Guide
   Description of the software coding standard, interfacing, and methods for software maintenance and updates