An important application of advanced technology to transportation engineering involves the development of advanced traffic management systems (ATMS). Any proposed traffic‐management action is essentially a forecast that the action will cause certain conditions, and uncertainty concerning traffic demand and/ or the values of model parameters will introduce random error between what is expected and what actually occurs. This paper considers in some detail the problem of forecasting whether or not a given set of freeway on‐ramp volumes are likely to cause overcapacity mainline demand. A simple model for the distribution of freeway traffic is considered, which leads to a straightforward interpretation of the impact of forecast uncertainty as a reduction in practial mainline capacity. The problem of efficient estimation‐of‐demand model parameters is then taken up; by embedding the demand model in a Markov‐process model of freeway traffic flow, it becomes possible to compare three estimation approaches via Monte Carlo methods. These estimators show noticeable differences in statistical efficiency, which translate into practically significant differences in freeway mainline capacity. This suggests that improvements in traffic management may be possible through substitution of efficient for less‐efficient statistical procedures.

Hierarchical traffic control that adapts to exogenous changes, optimizes system performance, and reduces local disturbances is one of the most effective advanced traffic management system methods for relieving congestion in freeway corridors. Optimal ramp‐metering control lies at the center of such a hierarchical control system. However, current ramp‐metering control strategies are not truly dynamic, are not optimal, or consider only parts of the freeway corridor. This paper presents an optimal ramp‐metering control method to alleviate congestion in the interacting corridor components, including freeway, parallel arterials, and connecting streets. The control formulation employs a continuum traffic‐flow model of the corridor dynamics, and the conjugate gradient method to search for optimal ramp‐metering rates according to the total travel time in the corridor. A test of the optimal metering for a simple one‐ramp segment of a freeway corridor is presented.

The development of advanced traffic‐management systems as a major component of intelligent vehicle/highway systems is targeted to address the complex problem of urban traffic congestion. The strategy includes real‐time diversion of traffic during congestion‐causing events, by making efficient use of the available capacities in the highway network. A conceptual framework for executing real‐time diversions is presented in this paper. The strategy envisages on‐line control and management of traffic through control centers and their surveillance equipment. The approach relies on real‐time traffic data to detect incidents and develop rerouting plants to benefit motorists. For this purpose, a model has been developed to estimate traveler destinations from traffic data. The dynamic nature of the problem is captured through a traffic assignment/simulation model, which can predict traffic conditions that would prevail in the alternate routes. A knowledge‐based expert system is also proposed to estimate traffic delays, and to evaluate and choose alternate routes. This research is being applied to the northern Virginia urban area as a case study.

Freeway‐incident‐management (FIM) programs are receiving growing attention, since they have the potential of generating substantial savings for highway users. The goal of any incident‐management program is the minimization of incident delay through the rapid restoration of the freeway capacity. The most important aspect of freeway‐incident management is the servicing and the removal of the incidents. Currently a number of FIM programs use a fleet of trucks for the quick restoration of freeway capacity. Although the deployment of these traffic‐flow restoration units (TFRUs) is an important component of freeway‐management operations, the literature lacks analytical models that can be used to rationalize the deployment of the TFRUs. The present paper proposes an integrated methodological framework for the minimization of freeway‐incident delays through the optimum deployment of TFRUs. The proposed model consists of three basic modules. The first module determines the number of required TFRUs and their service territories. The second module simulates the generation of freeway incidents and the traffic‐flow restoration operations to estimate the total incident clearance time for each incident. Finally, the third module estimates the freeway‐incident delay based on the total incident clearance time and the geometric and traffic characteristics of the freeway under study. The proposed model can be used to determine the number of TFRUs, and their dispatch policy, to achieve a threshold value of freeway‐incident delay.

The automation of urban freeways is intended to reduce travel time costs, reduce direct (distance) costs, improve the safety of travel, create smoother vehicle operation, increase freeway lane capacity, and improve the comfort of travelers. This study performs a financial analysis of the first four of these effects of automation on present urban travelers by estimating the financial costs of automating vehicles (net of the savings on fuel and insurance), and calculating the break‐even values for the speed increases needed to offset these costs. The analysis shows that automation will benefit heavy trucks and buses. Automation will also be cost‐effective for auto commuters if large, but plausible, freeway speed increases can be obtained. Automation in the future (when nonautomated freeway speeds will be lower) will be beneficial for more users, since the break‐even speed increases will be lower than their present values. The results of this analysis are very sensitive to assumptions regarding the cost of the automation devices and the changes in annual insurance payments.

Multiple period optimization models are developed that may be applied to several types of bus transit systems including feeder routes to transfer terminals, radial routes to activity centers, and zonal service operations. Decision variables including zone size, route length, route spacing, and service headway are optimized in closed form either independently or jointly. Although the service headways may be separately optimized for each time period, the route lengths and spacings must normally be optimized at unique values over all time periods, while varying with location. Effects of system parameters, such as demand density, operating cost and speed, value of time, and line‐haul distance on the optimal route characteristics are identified. Guidelines for designing bus‐service networks are provided based on the analytic results obtained.

A technique has been developed to quantify the visibility of vehicles to drivers approaching, or stopped at, an intersection where vegetation intermittently blocks their clear line of sight. The technique yields visibility values associated with a specific intersection, movement of vehicles, and vegetative environment. A computer program developed around the technique allows a user to determine the effects of the size and locations of specific vegetative elements on the partial or total visibility of one vehicle from another vehicle's location. The software is used to analyze the effects of visibility from removing or modifying selected vegetation surrounding an intersection, or along the crossroads. The visibility technique is general and can be used in many types of visibility analysis. The paper provides an example using the technique to determine the visibility between moving crossroad vehicles. In another example the visibility that a driver stopped at a controlled intersection has of the crossroad and traffic on it is determined. The technique can be used alone or in conjunction with field observations for the planning or analysis of vegetation effects on intersection visibility ranging from residential to forest settings.

Improvement in impact simulation between vehicles and roadside safety hardware is investigated. The use DYNA3D, a nonlinear, explicit, three‐dimensional, public‐domain, finite‐element code for vehicle impact numerical calculations is described. A preliminary example problem of a spherical impactor and a circular plate is used to model an impact between two deformable bodies. Numerical qualitative and quantitative results are compared with other known solutions. Finite element models of an actual vehicle and some examples of the roadside safety hardware are discussed. As a practical example, an impact simulation of a compact car with a light post is examined. The paper shows that even relatively small numbers of degrees of freedom used in DYNA3D program can accurately predict kinematics of highway vehicle impacts. These results conclude a preliminary feasibility study to develop the next generation of roadside safety computer software for vehicle impact simulation and analysis.

A concrete pavement curls to a concave configuration when it is subjected to a negative temperature gradient, which results when the temperature at its bottom surface is higher than at its top surface. A gap may occur between the bottom of the slab and the subgrade if the temperature gradient is large. The present paper offers an analytical approach to the determination of displacement and stress distributions for a semi‐infinite slab and for an infinitely‐long slab of a finite width, which takes into account a gap that may occur under the slab resulting from curling. Based on the analysis, an approximate formula for the maximum stress in a finite slab is suggested. The solution presented herein is obtained by applying the plate theory to an elastic plate resting on a Winkler foundation. Therefore, it is a general elastic solution and applies to not only concrete but also other materials.

The primary purpose of this paper is to evaluate laboratory test procedures for measuring the fatigue response of asphalt paving mixtures. Available test methods are conveniently classified into the following categories: simple flexure, supported flexure, direct axial, diametral, triaxial, fracture mechanics, and wheel‐track testing. Criteria used to evaluate each method for its potential use as a laboratory standard included: (1) Ability to simulate field conditions; (2) applicability of test results for use in modeling pavement performance; and (3) simplicity. The three most promising methods are considered to be simple flexure, diametral fatigue, and tests based on fracture mechanics principles. Although not a fatigue test in itself, direct tension testing offers considerable potential as a simple surrogate for more complex fatigue tests. Finally, in most prior work, the maximum principal tensile strain has been used as the cause or determinant of fatigue damage. Other damage determinants, such as work strain, as well as other cumulative failure laws, such as constancy of dissipated energy, offer promising alternatives.

This study looks at the concept of airline safety posture. This concept is introduced to reflect how well an airline is positioned for safety operations. Fortunately, airline accidents are far too rare for meaningful statistical analysis of airline safety. However, the incidence of incidents that could represent safety hazards but do not necessarily result in accidents is relatively frequent and lends itself to such analysis. Difficulties encountered during operation are usually reported as service difficulty reports (SDRs). Despite the many problems in the reports, not the least of which is inadequate reporting, the writers use SDRs as an indicator of safety posture. A statistical analysis suggests that airline deregulation has not adversely affected the safety posture of airlines. It is also found that the safety posture of postderegulation new entrants is not significantly different from that of established airlines. There is evidence that the larger carriers have a better safety posture than the smaller ones, and that service difficulties increase with stage length.