Alignment Analysis and Comparison Techniques for Small Railroad Projects in the 21 St Century

The current guidance provided for alignment studies stems largely from Wellington’s “Economic Theory of The Location of Railways” which discusses the problem of minimizing grades and curves on a transcontinental scale. However, modern engineers often find themselves working on a less grand scale with shorter projects such as industrial spur build-ins and urban by-passes, and needing to consider a host of engineering and environmental factors other than railroad geometry to complete a modern railroad alignment study. This paper describes alignment analysis and comparison techniques that have been used successfully in the development of preferred railroad geometry for such projects ranging from five to 50 miles in length. Two main techniques are highlighted: indexes for comparing grades and curves on short alignments, and the matrix approach to alignment analysis and comparison. The matrix approach allows a particular alignment to be evaluated on the basis of multiple criteria, each considering several factors. To avoid bias in the creation of the matrix, each evaluation area is given a weight in advance of the study by the owner. Once alignments are established, the evaluation is made in the form of a score, including those criteria and factors where the observed data is qualitative and not quantitative in nature. The individual alignment scores are then multiplied by the weights to form an overall alignment score. This overall score can be directly compared to that of other alignments to make decisions regarding a preferred alignment and a final recommendation to the owner. C. Tyler Dick, P.E. 3 INTRODUCTION In the current environment of railroad capacity expansion, an increasingly common task assigned to a railway engineer is the comparison of several alternative alignments for a new rail line. The basic criteria for railroad alignment comparison and route selection stem largely from the classic text by A.M. Wellington titled “Economic Theory of the Location of Railways” that describes the ideal railroad as that taking the flattest, straightest and shortest route between two points. While Wellington discusses the problem of minimizing grades and curves on a transcontinental scale, modern engineers often find themselves working on a less grand scale with shorter projects such as industrial spur build-ins and urban bypasses, and needing to consider a host of engineering and environmental factors other than railroad geometry to complete a railroad alignment study. In addition, remote sensing and computer design programs allow multiple alignment alternatives to be generated in a fraction of the time it took Wellington to develop a single route in 1887. The need to simultaneously evaluate a number of routes or alignment alternatives with respect to multiple engineering, environmental and social factors led to the development of a matrix analysis approach for railroad alignment studies. The process was adapted from practices which are more commonly used in general transportation planning and has been refined over the course of several railroad alignment studies. This paper will outline the matrix analysis approach, including descriptions of the various evaluation categories and methods of weighting and scoring. An important component of the matrix analysis approach is the calculation of indexes that allow quick and efficient comparisons between the grades and curves on multiple short alignments. These indexes will be described in more detail following the description of the matrix analysis approach. C. Tyler Dick, P.E. 4 MATRIX ANALYSIS APPROACH The matrix analysis approach is used to compare multiple alignment alternatives under consideration for a railroad project. The alignment alternatives are selected such that they represent distinct routes with differing horizontal layouts. However, it is possible for alignment alternatives to have common segments, particularly near start and end points. The analysis does not require that the alignment alternatives have common start or end points. This is useful when studying a line into a new industrial plant where there are several possible locations to tie the line to an existing mainline. In the matrix analysis approach, each alignment alternative is judged relative to several evaluation categories. These evaluation categories are subdivided into multiple decision criteria against which the alignments are scored. The individual scores for each criteria are weighted and summed to produce a category score. These category scores are then weighted again and summed to produce a total score for the alternative. The total score derived through this “double weighting” system provides a means to directly compare the overall performance of each alternative relative to the various decision factors deemed important by the client. To make an effective comparison, each alignment alternative must be developed to the point where preliminary horizontal and vertical geometry has been established. If a more detailed survey of the study area has not been conducted, preliminary alignments can typically be developed using digital elevation data or topographic map contours available from the United States Geographic Service to model the existing ground. A more detailed comparison can be made if a very preliminary earthwork model is developed for each alignment. This model, made by a first pass of a generic subgrade slope template in a rail design program, not only provides C. Tyler Dick, P.E. 5 quantity information for cost estimation but also provides a footprint for the evaluation of environmental impacts and can illuminate potential constructibility issues. EVALUATION CATEGORIES In this railroad application of the matrix analysis approach, five evaluation categories are used to evaluate the engineering, financial, societal, environmental and political aspects of a railroad project. The five evaluations categories are: • Operational efficiency, mobility and safety effects • Cost effectiveness • Social and economic effects • Environmental effects • Public and agency support As mentioned above, each of these evaluation categories are further broken down into multiple criteria for which scores are determined, typically on a scale of zero to five, with zero being the least optimal and five being the most optimal. The criteria include quantitative factors that can be measured through field investigation (such as acres of wetland impact), examination of design features and geometry (such as ruling grade), and preparation of preliminary cost estimates. The criteria also include qualitative factors such as ease of implementation, social and economic effects, and public and agency support that cannot be measured directly but, with the aid of various sources of information regarding the alignment alternatives, engineering judgment can provide reasonable scores. In the following sections, the criteria for each evaluation category are described in more detail. C. Tyler Dick, P.E. 6 Operational Efficiency, Mobility and Safety Effects The criteria for the operational efficiency, mobility and safety effects are selected to provide a measure of how optimal an alignment alternative is from a traditional engineering perspective. That is, they attempt to measure how well the alignment minimizes length, curves and grades to produce a railroad that operates efficiently and safely. The decision criteria are: • Operational efficiency