The 1992 IRC SP 38 serves as an exhaustive guide for the Road Investment Decision Model (RIDM), a specialized instrument aiding engineers and planners in assessing the economic feasibility of highway initiatives across India. It details procedures for compiling input data, estimating various costs, projecting traffic growth, and generating comprehensive output reports to support strategic decisions related to road widening, maintenance, and investment.
Overview
The 1992 IRC SP 38 serves as an exhaustive guide for the Road Investment Decision Model (RIDM), a specialized instrument aiding engineers and planners in assessing the economic feasibility of highway initiatives across India. It details procedures for compiling input data, estimating various costs, projecting traffic growth, and generating comprehensive output reports to support strategic decisions related to road widening, maintenance, and investment.
Audience
Contents
Structure
This section introduces the RIDM and outlines its scope, including key formulas and tables that describe speed-flow relationships for different road classes and terrains, crucial for design and fuel use estimation.
Details hardware needs such as IBM-compatible PCs with minimum 640 KB RAM and 132-column printers, software prerequisites including MS-DOS and Lotus 1-2-3, and step-by-step instructions for installing RIDM files from floppy disks.
Describes critical input parameters like project identification, road dimensions, analysis timeline, roughness values, traffic volumes, growth rates, and economic factors with their units and limitations.
Presents formulas for speed-flow for various vehicle types and terrains, including the application of minimum speed cutoffs and traffic growth considerations.
Explains internal calculation of VOC based on speed-flow models, the impact of congestion on VOC with specific multipliers per vehicle category, and the generation of VOC-related tables and graphs.
Covers conversion of financial costs to economic costs using conversion factors, computation of net present value (NPV) using discount rates, and graphical aids for decision-making.
Specifies user entry of construction and maintenance costs in financial terms and their conversion to economic costs with illustrative formulas and notes on endogenous VOC and travel time cost calculations.
Describes modules for data input, damage calculation using mechanistic-empirical approaches, output generation including pavement life and distress profiles, and instructions for running the program.
Details the structure of output reports including project, geometric, traffic, roughness, cost, and economic parameters, with guidelines for interpreting outputs to assist in economic viability and maintenance planning.
Highlights graphical appendices such as NPV vs discount rate, roughness over time, and VOC trends, and advises on usage for project appraisal and lifecycle cost analysis.
Discusses economic evaluation of different investment options using NPV calculations, sensitivity to discount rates, and incorporation of roughness and VOC models to compare phased and full construction alternatives.
Summarizes appendices containing fuel consumption formulas, input templates with example data, and key graphs for NPV, roughness, and vehicle operating costs that underpin the RIDM analyses.
Frequently Asked
The RIDM requires an IBM-compatible PC or PC-XT/PC-AT system with at least 640 KB RAM, a colour or monochrome monitor, and a 132-column printer. The software runs from a 5.25-inch double-sided double-density floppy disk and is compatible with DOS-based operating systems commonly used on early IBM PCs. Installation follows a specific procedure involving copying files from the floppy disk to the hard drive and setting up the printer for proper report output.
The model accounts for various vehicle types—cars, buses, trucks, and two-wheelers—using specific speed-flow equations tailored to road type and terrain. It applies a minimum speed threshold to avoid unrealistic travel time computations and integrates traffic growth rates to dynamically adjust vehicle operating costs. Congestion effects are modeled by applying vehicle-specific congestion multipliers when traffic volumes exceed design service capacity, ensuring accurate representation of traffic mix and growth impacts.
The economic evaluation encompasses construction costs (initial capital outlay), maintenance expenses (ongoing repair and upkeep), and road user costs, which include vehicle operating expenses, travel time costs, and accident-related costs. Financial costs are systematically converted to economic costs to reflect true resource utilization, ensuring a comprehensive analysis of both direct and indirect project impacts.
Vehicle operating costs are internally calculated using specific equations that factor in speed, road roughness, and gradient characteristics for each vehicle type. For example, truck VOC incorporates terms related to speed, roughness, and rise/fall. Travel time savings are derived from speed-flow relationships by comparing travel times before and after improvements, with a minimum speed floor of 10 km/h applied. These savings are then multiplied by vehicle volumes and assigned values of travel time to quantify economic benefits.
Yes, the RIDM allows assessment of staged or phased construction approaches alongside full construction alternatives. Users can specify different carriageway widths, pavement designs, and construction sequences. The model facilitates sensitivity analyses on unit costs, traffic growth, and design parameters, enabling comparative evaluation of multiple strategies to identify the most cost-effective and feasible investment plan.
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