Edward K. Morlok

An efficient approach to solving the road network equilibrium traffic assignment problem

This paper presents a solution technique that requires only the solution of a sequence of shortest route problems, such as computing time for the one dimensional searches being insignificant. The computing time for finding an approximate solution to the equilibrium problem was less than that required by the simplex method by orders of magnitude even on a fairly small network. For larger problems the savings would be even greater, since for multi-commodity network problems the number of constraints grows as the square of the conservation of flow and non-negativity constraints used explicitly in this technique. Preliminary computational results indicate that the number of shortest route subproblems for a network equilibrium problem with several hundred nodes will not be excessive; thus the solution approach presented appears very promising for large network equilibrium problems.

Improving the energy efficiency of freight in the United States through commodity-based analysis: justification and implementation

Abstract Efforts to reduce energy use in freight transportation usually center around “mode-based” approaches, namely improving the energy efficiency of energy intensive modes, such as truck, and shifting more freight to energy efficient modes, such as rail. In the first part of this paper we review the recent trends and future prospects for these mode-based approaches, finding that despite substantial improvement in the technological efficiency of freight modes and robust growth in the use of intermodal rail since 1980, total freight energy use across all modes in the US has grown by approximately 33%, with proportional growth in carbon emissions. In the second part of the paper we propose use of a “commodity-based” approach, in which freight energy use is disaggregated by contribution of major commodity groups, in order to support efficiency improvement at the commodity level. Two potential applications of the commodity based approach, namely (1) life cycle analysis of energy use for major commodity groups and (2) spatial analysis of freight patterns, are demonstrated using the 1993 US Commodity Flow Survey data. Results of these preliminary findings suggest that commodity groups vary widely in the ratio of energy use in production to energy use in transport, and that for many commodity groups, there may be substantial opportunities for saving energy by redistributing flow patterns. Through development of the commodity-based approach, we also identify the collaborative involvement of shippers and carriers as a key point in improving energy efficiency, since it can be used to both make the mode-based approach more effective and address new issues such as the underlying growth in tonne-km. Benefits for air quality and other transportation issues are also discussed.

A model for medium-term operations planning in an intermodal rail-truck service

This paper describes a model developed for medium-term operations planning in an intermodal rail-truck system. It was motivated by the need to redesign such systems to produce 1. (1) more reliable service, 2. (2) multiple service classes, and 3. (3) better equipment and facility utilization. The model is an integer linear program, which is computationally difficult to solve. A heuristic procedure was developed which provides excellent solutions, generally within 1% of the known optimal solution to the relaxed (non-integer) problem. Thus the model and heuristic could be used on large networks. Uses of the model and possible extensions are briefly discussed.

Short-haul rail intermodal: can it compete with trucks?

Intermodal traffic, that is, truck trailers or ocean containers handled on special rail equipment, is the fastest-growing segment of rail traffic. Between 1990 and 2000, rail intermodal grew at an annual rate of 4.6%—much faster than rail carload freight, which grew at an annual rate of only 1.4%. However, during the same period, truck tonnage grew at an annual rate of 6.9%, and air cargo at a rate of 17.9%. The growing rail intermodal is expected to overtake coal as the single largest source of revenue for freight railroads in the year 2004. But railroad intermodal tonnage is not growing as fast as truck traffic, and market share is consequently falling. This is a problem: with total freight traffic projected to grow 57% by the year 2020, all the increased traffic will have to be accommodated on the highway network. The introduction of double-stack rail cars in the 1980s dramatically reduced rail haul costs, and it made intermodal traffic competitive at distances of 500 mi or so, whereas previously rail could compete with trucks only at distances of about 750 mi or more. Still, most rail intermodal traffic remains long haul. Three-quarters of all truck tonnage moves distances of less than 500 mi, and rail does not compete in this market. Rail haul costs are developed for a number of short corridors, and it is demonstrated that although double-stack usage has lowered line haul costs, terminal and drayage costs remain high. If these costs can be reduced, rail intermodal can be competitive even in short-distance corridors. Several ways to lower these costs, both by industry initiatives and by public investment, are proposed. Without some action by the public sector, short-haul rail intermodal will continue to be noncompetitive, and highway truck traffic will continue to grow.

FREIGHT ENERGY USE DISAGGREGATED BY COMMODITY: COMPARISONS AND DISCUSSION

The analysis of energy consumption in freight transportation is almost always approached by disaggregating overall energy consumption by mode, which then provides a basis for understanding trends and underlying factors that influence them and for developing conservation policies. Another important approach is to disaggregate by commodity, because it is commodity flows that generate the modal vehicle flows and hence the modal energy consumption in transportation. Thus changes in energy use by commodity are important factors in understanding trends in energy consumption and may provide a basis for energy conservation policies centered on industries using transportation. Total freight energy consumption is estimated for a range of commodity groups using an activitybased approach to energy consumption, where total freight activity is decomposed into components by mode and by commodity group, and then each component is multiplied by an intensity estimate to calculate total energy use for that commodity group. Two important findings are discussed: (a) commodity groups with high energy growth between 1972 and 1993 had a combination of substantial ton-mile growth and modal shift to truck, and (b) commodity groups of finished products with a high average value per ton in general have a much higher average freight energy intensity than raw materials with a low average value per ton.

Improving Productivity in Intermodal Rail-Truck Transportation

This paper has two purposes. One is to discuss and define the concepts of productivity and quality as they apply to transportation, particularly freight transportation, and to identify the similarities and differences with other service industries (e.g., banking and social services). The second purpose is to describe how productivity and quality improvements can be achieved in the trucking (or drayage) portion of intermodal rail-truck service, and the implications of these for market penetration.

ESTIMATING THE CAPACITY OF FREIGHT TRANSPORTATION SYSTEMS: A MODEL AND ITS APPLICATION IN TRANSPORT PLANNING AND LOGISTICS

The issue of adequate capacity in the freight transportation system to accommodate growing cargo volumes is now becoming a major public policy concern. The problem of extraordinary rail line congestion and service failures in connection with the recent Union Pacific–Southern Pacific merger has galvanized attention to the problem, but the issue extends far beyond the rail system to other modes and contexts. The concept of system capacity (as opposed to link or facility capacity) is developed, and prior literature is reviewed for approaches to estimating it. A model that was developed from the most promising of these is presented. This model is multimodal in concept and is intended to be applicable to any vehicular freight mode. The model is tested through application to a portion of the rail network, and results are assessed for reasonableness and utility. Finally, the applicability of the model and approach to various capacity-related questions is described and discussed.

An Analysis and Comparison of Behavioral Assumptions in Traffic Assignment

This paper compares modeling of traffic flow on networks in such a manner that total user cost is minimized with the modeling of flow so that an equilibrium is achieved. A detailed comparison of the output from these two models is presented for a 76 arc, 24 node sketch planning network used to model the city of Sioux Falls, South Dakota. The results indicate that the difference between the two sets of flows is small enough to justify the simplifying assumption that total user cost is minimized. Such an assumption is often made in network design or link addition models to achieve computational ease, particularly in the context of multiple objectives.

Boarding and alighting injury experience with different station platform and car entranceway designs on US commuter railroads.

Commuter railroad systems in the US employ three combinations of station platforms and car entranceways. These are high-level platforms with remotely controlled doors and level entranceway (HL-RC), low-level platforms (just above the rail) with steps and remotely controlled doors (LL-RC), and a mixture of the two platform types with a correspondingly more complex, partly manual, door and entranceway arrangement (ML-MO). Much controversy exists over which type of platform/entranceway is better. This seemingly small feature significantly impacts many performance characteristics of these systems, including cost, speed, and boarding and alighting accidents. Northeastern systems are generally moving toward the mixed platform design or all high-level platforms, while systems elsewhere are generally selecting the low-level design. Data on actual accident experience for 1995-2000 are analyzed to determine the effect of platform/entranceway type on passenger and employee injuries. Passenger injury rates on systems with the HL-RC design are lowest, with LL-RC systems next, and ML-MO systems having the highest rates. Employee injury rates are the least on LL-RC systems, but higher on ML-MO and HL-RC systems. Systems with a mixture of high and low platforms (ML-MO) experience a higher overall (combined passenger and employee) injury rate than the other two designs. The implications of these results for both the modernization of existing systems and the design of new systems, in the US and abroad, are discussed.

SHORT RUN SUPPLY FUNCTIONS WITH DECREASING USER COSTS

This note shows, with an example, that user costs on transportation systems need not remain constant or increase with increasing volume, even with design and operational options fixed.