Real-time traffic incident response strategies deal with the determination of optimal resource allocation policies in response to traffic incidents occurring on a network. Such strategies also should address the effect of loss in coverage caused by the nonavailability of response vehicles that currently are serving certain primary incidents. In this paper, we first formulate a mixed-integer programming (MIP) model MIMR-1 for the multiple-incident multiple-response (MIMR) problem using standard modeling techniques. The effect of loss in coverage is reflected in the model by including in the objective function a new term related to an opportunity cost for serving future (secondary) incidents that might occur probabilistically on the network. We next present an alternative, equivalent MIP model (MIMR-2) that injects a particular structure into the problem. This is shown to yield a dramatic improvement in the performance of the commercial software package CPLEX-MIP when applied to this revised model in comparison with its application to MIMR-1. Furthermore, for certain special cases of the MIMR problem, efficient polynomial-time solution approaches are prescribed that yield a far superior performance over CPLEX-MIP. An algorithmic module composed of the developed specialized solution procedures, model MIMR-2, and a prescribed heuristic scheme, has been incorporated into a real-time area-wide incident management decision support system.

A recent project simulating automated freeways in the Sacramento, Calif., region is described. Of special interest is the economic welfare model applied in this project. It was found that travel and emissions increase with capacity. Traveler economic welfare increased (over the no-build case) only in modest [97 km/h (60 mi/h) or one lane] automated highway system scenarios. Peak-period freeway tolls and parking pricing with land-use intensification at outer freeway ramps greatly increased user benefits, as did automating only single HOV lanes. Future automated highway system research should consider incremental automation (one lane at a time), tolls and parking cash-out, and land-use intensification near freeway ramps.

In recent years, land development professionals from various disciplines have advocated narrowing city streets as a means to slow speeds and improve the urban environment. This paper reports the findings of a study of relationships among urban street function (i.e., arterial versus local traffic), width, and resulting speed. Crash data for the roadways studied also were considered. The objective was to determine if the wider streets did in fact have more objectionable traits (e.g., higher speeds or crash rates) than did the narrower streets, taking street function into account. Six two-lane streets in a small city were considered; the predominate focus of the study was an old neighborhood with streets in a grid layout. The findings suggest that street width may play a small role in vehicle speed, but other factors such as trip function may be more significant determinants of the average and 85th percentile through vehicle speeds. From this study, one also can infer the need to segregate traits of through vehicles from local vehicles when collecting speed data for the purpose of contrasting the behaviors on various streets.

A gap acceptance study was performed at a T-intersection at which left-turn traffic on the through leg had the right-of-way. A number of methods were used to model the critical gap size at this atypical intersection. The critical lag and gap values varied according to the method used to compute them, and the different movement or conflict combinations exhibited different critical values. On the approach required to stop, representative values ranged from a 7.8-s critical gap with the higher priority traffic stream from the right, to a 2.2-s critical lag with the highest priority traffic from the opposite direction. The drivers involved in certain movement or conflict patterns at this intersection with the atypical right-of-way pattern were quite comfortable with short lags and gaps.

Knowledge of the cost and production structure of transit systems can be instrumental in uncovering an array of important information regarding their operation. Optimal fleet size and pricing, average and marginal cost, and the potential for success of deregulation and privatization efforts can be addressed successfully when the cost structure of transit systems is known. Research on the cost structure of mass transit systems using panel data frequently shows conflicting results with respect to issues such as economies of scale and density, and factor substitution elasticities. In this analysis we extend prior research in two significant directions. First, we control for cross-sectional heterogeneity that may otherwise seriously bias the resulting parameter estimates. Second, we make an explicit effort to capture differences in the economies of scale between large, medium, and small transit systems. Based on panel data for fixed-route public transit systems, the results indicate that transit services are characterized by a nonhomothetic production function, exhibiting returns to density and scale that depend on the size of the transit firm.

This paper is concerned with the modeling of the complex demand-supply relationship in urban taxi services. A neural network model is developed, based on a taxi service situation observed in the urban area of Hong Kong. The input consists of several exogenous variables including number of licensed taxis, incremental charge of taxi fare, average occupied taxi journey time, average disposable income, and population and customer price index; the output consists of a set of endogenous variables including daily taxi passenger demand, passenger waiting time, vacant taxi headway, average percentage of occupied taxis, taxi utilization, and average taxi waiting time. Comparisons of the estimation accuracy are made between the neural network model and the simultaneous equations model. The results show that the neutral network-based macro taxi model can obtain much more accurate information of the taxi services than the simultaneous equations model does. Although the data set used for training the neural network is small, the results obtained thus far are very encouraging. The neural network model can be used as a policy tool by regulator to assist with the decisions concerning the restriction over the number of taxi licenses and the fixing of the taxi fare structure as well as a range of service quality control.

A multicriteria decision-making framework to aid the selection of roadway improvement projects is developed, based on the needs of a state highway agency. Three major factors—crash-risk reduction, performance improvement, and project cost—are addressed in a multicriteria tool that enables the comparison of even very diverse projects on a common ground and provides information on the trade-offs that come with the selection of one or the other project. The contribution is unique in that no overall scores need to be generated, acknowledging that although decision support can be provided, project selection will be made by human decision makers, who should be able to incorporate additional information, e.g., environmental or aesthetic impacts, not necessarily available to the analyst. The use of this framework primarily is seen at an early stage of planning, which generally is characterized by the absence of detailed information for the potential projects. A real-world application of the proposed methodology is demonstrated, and various potential applications and decision-making contexts in which the use of this tool could be beneficial are highlighted.

The process of transportation planning begins with an assumed land use and then projects future traffic volumes. To determine land-use limitations as a function of the capacity of the transportation system, we reversed the direction of the planning process, beginning with transportation system characteristics as the independent variable and employment and population as dependent variables. We ultimately developed a direct estimation model. This technique directly estimates zonal trip ends based on transportation system variables that include link volumes, roadway types, travel distances, and the geographical position of the zone. Additionally, we regressed retail employment, nonretail employment, and population to zonal trip ends. We calibrated this model for the 1967 base year in the Charlottesville, Va. area and then applied it for the 1979 forecast year. We then used lessons learned to calibrate the model for the 1979 base year (a training set of data) and apply it for the 1990 forecast year (a test set of data). We suggest how this model formulation might be interpreted to yield land-use limits as a function of traffic volumes and discuss subsequent application of this approach to consider policy options that arise in the context of transportation planning.

Pavement surface deflection basins provide valuable information for the structural evaluation of flexible pavements. Surface deflection measurements are rapid, inexpensive, and nondestructive and are used frequently as an indicator of pavement structural capability and performance potential. In this study, falling weight deflectometer testing results on the conventional flexible pavements (asphalt concrete surface, granular base/subbase) and aggregate-surface/surface-treated test sections in the low-volume road loop at the Minnesota Road Research Project were analyzed to evaluate the effect of granular material quality on the pavement structural response. Asphalt concrete (AC) modulus and subgrade “break-point” modulus were back-calculated using algorithms previously developed at the University of Illinois. The surface deflections were normalized to the same AC modulus and subgrade modulus. The analyses show a limited effect of granular material quality on the pavement deflection response in the case of conventional flexible pavements. Because of higher granular layer stresses, the granular material quality effects on the pavement surface deflection response of surface-treated/aggregate-surface pavements are significant. Increased AC thickness reduces the effect of granular base quality on the pavement deflection response.

Warping of portland cement concrete (PCC) pavements is the result of temperature and/or moisture gradients in the pavement structure. So far, the focus has been on studying and modeling temperature gradients caused by the relative ease of measuring temperature gradients in PCC as compared with the measurement of moisture gradients. This paper provides the methodology for determining the moisture content in nonreinforced PCC pavements by relating the moisture content to the dielectric constant. This relationship is a second-order polynomial equation with a 95% confidence band for a range of water contents from 4 to 11%.

This paper describes analysis of pavement deflection data collected by the Transport Research Laboratory at two experimental road sites in England during 1960–1985. Measurements of Benkelman beam deflections together with records of traffic loading were taken at 6 to 12 month intervals. The analysis investigates the deflection trend as a function of road base material and thickness. The deflection trend was represented by a negative exponential curve form. Engineering aspects of the curve form were extracted and statistically analyzed. The results obtained focus on the dependency of deflection progression on both road base material and thickness, which are shown to act either jointly or singly, depending on the engineering characteristic of the pavement deflection trend.

The most common practical way to simplify the structural analysis of airfield pavements is the use of equivalent single wheel load models instead of the actual gear of the aircrafts. As the accuracy and reliability of these models strongly affects the design and evaluation of airfield pavements, there is considerable need to investigate both system approaches. The first one, which uses a constant value for the pressure while the radius is variable, is currently under use by the aircraft classification number—pavement classification number method of the International Civil Aviation Organization, but despite this fact it proved to be inadequate to express the aircraft loading in many situations. On the contrary, according to this study, the second model, which has a constant value for the radius while the pressure varies, is more reliable, and it can be an interesting alternative. Thus, based on this model, an aircraft loading index is introduced, which aims to be a simple and reliable factor for expressing the severity of the loading of the aircrafts and a utility for several matters related to the airfield pavement applications.