Substantial increases in truck weights and dimensions have occurred over the past decade and these changes have important implications for the criteria used for the design of various components of highway infrastructure. The paper reviews the findings of a wide range of studies on truck characteristics and the ways in which these characteristics influence the design criteria. The truck properties examined include braking distances, rollover thresholds, traffic capacity impacts, speed profiles on grades, passing sight distances, low‐speed offtracking at intersections, intersection capacity and signal timing, force effects in bridges, and pavement axle‐load equivalencies. The paper concludes that the many design procedures used for infrastructure design should be revised to incorporate this new evidence.

A consistent and theoretically rigorous approach is presented, using the principles of dimensional analysis, and leading to a closed‐form back‐calculation procedure for a two‐layer slab‐on‐grade pavement system. The equations required are derived and evaluated for four fundamental combinations of loading and support conditions. A short computer program has been coded, called ILLI‐BACK, to implement the method on a personal computer. The execution time per back‐calculation is trivial (a fraction of a second). This procedure simplifies considerably the effort required in interpreting nondestructive deflection data. It is much more efficient and accurate than current approaches, allowing the use of any one of the measured sensor deflections in the back‐calculation process. The concept proposed is powerful and versatile, and can easily be adapted for a wide variety of other applications, involving both rigid and flexible pavement systems.

A procedure for siting major new airports is proposed and validated by example of its successful use in Australia to obtain agreement on the location of the second Sydney airport. The technique differs from the traditional master planning approach. It recognizes explicitly our inability to predict the future, and thus confronts the real range of risks that may exist. In such risky situations, the optimal solution involves: (1) Insurance, as flexibility to meet possible future conditions; and (2) a strategy for dealing with these contingencies as they develop. Securing a site for a new airport provides the insurance for future needs; acknowledging that the facility to be built depends on future circumstances provides the basis for the strategy.

This paper presents the operational issues and results of implementing real‐time headway‐based reliability control along candidate bus routes operated by the Massachusetts Bay Transportation Authority in 1987. The procedure involves holding buses at a control point on the route until a prescribed minimum headway is achieved. Headway‐based control strategies apply to high‐frequency transit routes where headways are sufficiently short that travelers arrive randomly at bus stops without consulting a schedule. It is considered appropriate for correcting service disruptions that have already occurred, or for preventing propagation and further service degradation. The goal of this effort is to improve service reliability as perceived by travelers, as well as to allow for more effective utilization of operator resources. Failure by street supervisors to consistently follow holding instructions and data collection problems involving point checkers hampered the evaluation effort. Nevertheless, it appears that certain routes may benefit from holding actions. Where these improvements are measurable, dramatic operator savings, due to reduced vehicle requirements, may be realized. This depends on the extent to which passenger load, relative to vehicle capacity, may preclude the operator from taking maximum advantage of the derived service benefits.

A key issue in planning major highway reconstruction projects is the allocation of roadway space between the reconstruction activities and the motorists. Estimates of the travel impacts of alternative allocations are required to determine the appropriate use of roadway space. A review of available analysis tools and of experiences with traffic management during reconstruction led to the development of the travel impact evaluation process and the guidelines for selecting appropriate analysis tools presented herein. In summary, the magnitude of the capacity reduction (relative to traffic demand) on the highway being reconstructed determines the appropriate scope of the evaluation. If the capacity reductions are minor, then traffic is unlikely to divert from the reconstruction zone and the evaluation may be limited to the highway being reconstructed, in which case the evaluation could be performed using highway capacity analysis procedures or traffic simulation models. If capacity reductions are significant, then motorists are likely to change their travel patterns and the evaluation should be corridor‐wide, in which case an analysis tool with traffic assignment capabilities must be used.

This paper discusses the costs and benefits of computerized traffic record systems and the actions required to implement them. While it emphasizes the problems and opportunities faced by small transportation and public works agencies, many points apply equally well to other types of organizations. Observations are based largely on experience implementing a comprehensive package of traffic record‐keeping software called the Berkeley Traffic System (BTS). The paper characterizes the visible and hidden costs and benefits of computerization, and related problems. It also provides a checklist of points to consider in planning for local implementation.

This paper describes a research project performed as part of a clear zone implementation program for Huntsville, Alabama. A literature review and a field investigation program were the two major components of the project. Investigators visited the sites of 164 urban tree accidents to identify their characteristics. Time of day, day of week, accident severity, roadway geometry, pavement surface condition, lateral distance from the pavement to the tree, tree size, and tree density were among the characteristics investigated. Among the major findings were that: there were strong similarities between urban and rural tree collision patterns, but urban accidents were less severe; the outside of horizontal curves was highly over‐represented; and 80% of the collisions were within 20 ft of the pavement edge. Recommendations were provided for city ordinances and operating procedures for future tree plantings. A plan was also devised for retrofitting the clear zone concept to existing trees along city streets.

This paper focuses on regression and intervention modeling of Lexington/Fayette County specialized transportation, WHEELS, monthly riderships. The 1979–1985 time‐series ridership data are comprised of total monthly trips and their breakdown by passenger type, the passenger's ability to walk, and trip purpose. Intervention models from time‐series analysis properly replicated these monthly riderships. The superiority of intervention modeling when compared with regression analysis was found to be in capturing ridership seasonality, proper incorporation of the time‐lag structure, and the intervening events of fare and service changes. Post‐modeling analysis determined months of ridership peaks. The para‐transit planning and management utility of these modeling techniques in time‐series analysis is clearly evident. Although the selected models are dependent on the 1975–1985 data, the same methodology can be applied to any time‐series ridership data for short‐term demand modeling.