Airline hubbing can be viewed as a strategy to increase airline network efficiency and to reduce operating costs. Alternatively, hubbing can be viewed as a marketing strategy permitting airlines to achieve dominant market shares at their hub airports and to take advantage of market preferences for the increased frequancies that the strategy permits. This study inquires into the hypothesis that significant cost reductions can be achieved by hubbing. Using a detailed cost analysis of 13 airlines with different degrees of hubbing over the period 1976‐1984, we find no evidence of a relation between the degree of hubbing and cost levels. The current conclusion is that the explanation of hubbing is likely to be found in an analysis of airline marketing strategies and in market response to airline routing and networking decisions.

This study addresses safety issues associated with the operation of freeway high‐occupancy vehicle (HOV) lanes that are not separated by physical barriers from adjacent, general‐purpose traffic lanes. Accident frequencies and characteristics obtained from 14 months of operation of an HOV lane in the greater Los Angeles area, together with similar data for 6 years prior to the opening of the lane, are analyzed to evaluate the safety impacts of the lane operation. The analyses rely on comparisons of accident characteristics associated with the HOV lane to those associated with both temporal and spatial control groups. Changes in accident characteristics are also related to existing patterns of freeway congestion. The results of the case study indicate no adverse effect on safety conditions that could logically be attributed to the HOV operation; all of the changes in the patterns of reported accidents can be explained by changes in the location and timing of traffic congestion. Although no overall change in the exposure to accidents was found, there is a significant migration of accident locations due to the combination of relief of congestion in the project area and a corresponding creation of more severe traffic bottlenecks downstream of the project.

The growing volume of hazardous‐materials shipments and the potential consequences of a materials release have raised public concern and scrutiny over the safe handling and transport of hazardous cargo. This has prompted intensive regulatory review and technical studies directed at identification and resolution of critical issues impacting the safe transport of hazardous materials. This paper addresses these issues, both from the standpoint of what is currently known and for the development of an agenda for enhancing hazardous‐materials transport safety in the future. Attention is focused principally on those areas where the needs are particularly acute, namely the regulatory environment, information systems, accident analysis, hazard mitigation, risk assessment, routing, community preparedness, and incident management. The basis for this review is the condition of “Check pdf for missing text” ilar safety problems plague other industrial countries, it is expected that many of the conclusions and recommendations reported herein will have application to the international community.

This paper offers an addition to a family of previously proposed vehicle‐scheduling models for a demand‐responsive transportation system. The assumed operating environment consists of many‐to‐many travel demand, multi‐vehicle, advanced reservation, and time‐window constraint for pickup and dropoff times. The model builds vehicle schedules one vehicle at a time, maximizing the number of trip requests to be handled by each vehicle. The method follows a two‐step approach: building of an initial route, and insertion of additional trips into the initial route. In inserting trips to the initial route, the model checks feasibility of insertion for each trip first, and then identifies the maximum number of trips that can be inserted using a tree‐structured search technique. The proposed method is evaluated for a set of specific examples by examining the sum of time differences between the original and actual pickup and drop‐off times, and the number of vehicles required. The model is relatively straightforward in its computational procedure and offers possibilities of other applications.

The present investigation considers the prediction of the design hour volume from users' perspective. [The design hour volume concept from users' perspective was introduced in an earlier paper (Sharma 1986), which concluded that the type of road use is a significant variable that should be considered for appropriate design volume. Another finding was that to provide a more uniform service to the users, it is better to use different highest‐volume hours for designing different types of roads.] Linear regression models are developed in the present paper and tested using highway traffic data from the province of Alberta, Canada. The design hour volume from users' perspective is expressed as a function of the type of monthly and daily traffic data that are easily available to highway agencies. It is concluded that the design hour volume from users' perspective is predictable with as much accuracy as the traditional design hour volume where the thirtieth or some other highest hour of the year is chosen for design purpose. The paper also shows some example applications of the proposed models.

This paper examines the systemwide routing, of hazardous materials as a means of reducing the threat to the population residing along the links of an entire transportation network. A multi‐objective decision‐making model is used for the mathematical formulation of the routing problem. The proposed model includes the following objectives: (1) Minimization of risk; (2) minimization of risk of special population categories; (3) minimization of travel time; and (4) minimization of property damages. A capacitated and a noncapacitated version of the multiobjective routing problem are presented. A hypothetical network is used to display the applicability of the proposed model. For the example under consideration it is shown that the imposition of capacity constraints on the links of the network tends to distribute the risk in an equitable manner while it increases the total risk by 35%.

The paper presents results of research carried out to evolve suitable evaluation criteria for admixture stabilization for problem laterite where Portland cement is used as the stabilizer and hydrated lime as the admixture. The results presented show that there are promises of increased strength gain with time. In addition, high durability is recorded for the range of mixes tested. Accordingly, unconfined compressive strength (UCS) and California bearing ratio (CBR) values of $1.38N/{\mathrm{mm}}^2$ and 90%, respectively, are recommended as evaluation criteria for this form of stabilization for problem laterite. This high value of UCS compared with the conventional value of $1.08N/{\mathrm{mm}}^2$ for lime stabilization is justified by the superior pozzolanic nature of the cementitious reaction in this admixture stabilization.