In the purely theoretical approach of pavement design, percentage fatigue cracking is related to damage in a probabilistic manner according to the Miner’s law. Two methods that are currently widely in use are based on assumptions of damage distribution. One method assumes fatigue damage being normally distributed, while the other one assumes fatigue damage being lognormally distributed. Since mechanistic-empirical pavement design and pavement management require precise forecasting of pavement fatigue cracking, much effort should be taken to characterize and predict fatigue cracking in terms of damage distribution. In this paper, we formulate the probability density distribution of fatigue damage of flexible pavements according to the underlying structure of fatigue cracking equations so that pavement fatigue-cracking damage can be interpreted in a more meaningful way. Numerical computation is conducted for a case study. It is found that damage is neither normally nor lognormally distributed. It is therefore recommended that methodology and damage distribution model established in this paper be used in practice to predict damage distribution and percentage cracking so that a better estimation of fatigue cracking can be made.

This paper presents an evaluation of long-term performance of an alternative flexible pavement design referred to here as stone interlayer pavement. This pavement design was introduced to reduce/defer reflective cracking experienced with soil-cement bases. The stone interlayer pavement consisted of a crushed limestone base on top of a cement-stabilized base. The performance of the stone interlayer pavement was compared to that of the conventional pavement design with a cement-stabilized base. The stone interlayer and conventional pavements were constructed on State Highway LA-97 near Jennings, Louisiana. Both pavements were monitored for 10.2 years after construction. During the evaluation period, pavement distress surveys, testing of roughness and permanent deformation, and evaluation of pavement structural capacity using dynamic nondestructive testing were conducted. Additionally, as a part of the Louisiana Transportation Research Center accelerated pavement testing research program, both pavement designs were tested to failure under the Accelerated Loading Facility in Port Allen, Louisiana. The results of this investigation showed a superior performance of the stone interlayer pavement over the conventional soil cement pavement as tested in the field as well as under accelerated loading.

Several methods for distributing highway superelevation (e) and side friction (f ) have been presented by the American Association of State Highway and Transportation Officials (AASHTO). Based on a subjective analysis, AASHTO has recommended the curvilinear distribution method. This paper presents an objective method that distributes superelevation using mathematical optimization. A safety margin is defined as the difference between the maximum limiting speed (corresponding to $f_{\max })$ and the design speed. The objective function of the model minimizes the overall variation of the safety margin along the highway (aggregate analysis) or the individual variations of the safety margin between adjacent curves (disaggregate analysis). Both objectives maximize highway design consistency. The model includes constraints related to the maximum side friction, minimum and maximum superelevations, centripetal ratio, and safety margin. The e and f distributions can be discrete values with no specific mathematical shape or follow a general quadratic curve with a parameter determined by the optimization model. Application of the model was illustrated using two examples, and the results show that the design consistency obtained by the model is considerably better than that obtained by the AASHTO methods.

A case-based reasoning (CBR) model is presented for freeway work zone traffic management. The model considers work zone layout, traffic demand, work characteristics, traffic control measures, and mobility impacts. A four-set case base schema or domain theory is developed to represent the cases based on the aforementioned characteristics of the problem. It includes a general information set, a problem description set, a solution (or control) description set, and an effects set. To improve the interactivity of the CBR system and its user-friendliness, a hierarchical object-oriented case model is developed for work zone traffic management. The model is implemented into an intelligent decision-support tool to assist traffic agencies in the development of work zone traffic control plans and to better design and manage work zones for increased mobility and safety. Three examples are presented to show the practical utility of the CBR system for work zone traffic management.

Auto manufacturers have begun to market an adaptive cruise control system (ACCS) as an option that promotes driver safety. This paper examines how the presence of vehicles equipped with ACCS affects stability and safety of a flow consisting of both ACCS and non-ACCS vehicles. We focus on the effects of the short perception-reaction time of the ACCS vehicles. Given a perturbation to the first vehicle in the platoon, the behavior of each following vehicle is tracked for changes in headway, speed, and location using a simulation model. A fuzzy rule based car-following model is selected as the test-bed for simulation after reviewing other models. Simulation is conducted under many scenarios with respect to the number of ACCS vehicles, the perception-reaction times, and the ACCS vehicle’s placement in the platoon. We introduce two measures to evaluate stability and safety: one, the pattern of changes in the minimum spacing for each pair of two consecutive vehicles, and two, the total time during which the following vehicles cannot stop safely. It is found that, generally, the shorter perception-reaction time of the ACCS vehicles can shorten the process of achieving stability, and also can promote safety to both the ACCS and the non-ACCS vehicles under congested conditions. The findings generate an interesting debate on the issues of the benefits that non-ACCS vehicles enjoy as a result of the presence of ACCS vehicles in the traffic flow.

A new concept to estimate the passenger car unit (PCU) of different types of vehicles under mixed traffic conditions is presented. It utilizes the area, as opposed to only the length, and speed of a vehicle. Data were collected at ten sections of two-lane roads in different parts of India. The width of carriageway (this term is commonly used in India for the total width of the paved surface of a road excluding its shoulders) ranged from 5.5 to 8.8 m. All vehicles were divided into nine different categories and their PCU’s were estimated at each road section. It was found that the PCU for a vehicle type increases linearly with the width of carriageway. This is attributed to the greater freedom of movement on wider roads and therefore a greater speed differential between a car and a vehicle type. The capacity of a two-lane road also increases with total width of the carriageway and the relationship between the two follows a second-degree curve. This relationship is used to derive the adjustment factors for substandard lane widths and the results are compared with literature.

The efficient control of traffic on motorways or freeways can produce many benefits, including quicker journey times, fewer pollutant emissions, and reduced driver stress. If it were possible to accurately predict the future state of traffic on a motorway, active measures could be taken to forestall congestion and its attendant negative impacts. This paper presents an intuitive method of producing these forecasts using a pattern matching technique. The technique adopted is novel in that it is a multivariate extension of nonparametric regression that exploits the three-dimensional nature of the traffic state. The application and other facets of the technique are illustrated with actual data from the London orbital motorway. The technique is able to produce forecasts for two of the three traffic state variables with reasonable accuracy and is capable of application on site.

Real-time speed and vehicle-classification data are important inputs for modern freeway traffic control and management systems. However, these data are not directly measurable by single-loop detectors. Although dual-loop detectors provide speeds and classified vehicle volumes, there are too few of them on our current freeway systems to meet the practical ATMS (Advanced Traffic Management System) needs, and the cost of upgrading from a single-loop detector to a dual-loop detector is high. This makes it extremely desirable to develop appropriate algorithms to make single-loop detectors capable of performing the tasks of double loops. This paper presents just such an algorithm, i.e., one that uses single-loop measurements to provide accurate speed and vehicle-classification estimates. There are three steps in the algorithm: (1) to separate intervals with long vehicles (LVs) from those without; (2) to use measurements of intervals without LVs for speed estimation; and (3) to identify LV volumes for the intervals with LVs using the estimated speed. Preliminary tests for both spatial transferability and temporal transferability of the algorithm were performed, and the results were encouraging.

This paper presents a microscopic stochastic simulation model developed to emulate the traffic movement at signalized intersections and estimate vehicular delays including the acceleration/deceleration delay. The structure and overall logic of the model is discussed in this paper, and validation work using field data proved the model validity to represent real systems. The simulation model was applied to experiment 48 cases and evaluate the impact of the cycle length, approach speed, and degree of saturation on vehicular delays. The impact of each parameter was assessed and analyzed. It was found that the acceleration/deceleration delay component is directly proportional to the cycle length and degree of saturation and inversely proportional to the approach speed. In addition, the impact of approach speed is not significant compared to that of the other two parameters. Furthermore, the ratio of total to stopped delays was also estimated and found to vary between 1.5 and 3.0. The relationship between simulated and the Highway Capacity Manual (HCM) 2000 model delays was analyzed for the 48 cases and represented by a linear regression model with $R^2$ of 94.6%. This relationship indicated that simulated delay is higher than the HCM delay by about 6%, and this may be attributed to the different methods applied in both models for calculating delay due to acceleration and deceleration at the signalized intersection.

Transit route network design for urban bus systems involves the selection of a set of routes and the associated frequencies that achieve the desired objective, subject to the operational constraints. This can be formulated as an optimization problem that minimizes the total system cost, which can be expressed as a function of bus operating cost and passenger total travel time. In the first phase of a two-phase solution process, a large set of candidate route is generated using a candidate route generation algorithm. In the second phase, a solution route set is selected from the candidate route set using genetic algorithms, a search and optimization method based on natural genetics. The simultaneous route and frequency coded model proposed in this investigation considers the frequency of the route as the variable, thus differing from the earlier models in terms of coding scheme adopted. A sample study on a medium-sized network has established that the coding scheme adopted for the route network design enhanced the performance of the model.

Safe pedestrian movement is essential in all cities, but particularly in such densely populated cities as Hong Kong. This paper aims to investigate the levels of service (LOS) for stairways in Hong Kong Mass Transit Railway (MTR) stations. Space requirements and several qualitative factors were gleaned from the observation of pedestrian preferences and behavior. A pilot study was carried out before the pedestrian preference interview survey was conducted in a Hong Kong MTR station. On the basis of the survey results, six LOS design standards for stairways in Hong Kong MTR stations are proposed. The survey results are also compared with previous research findings. Lighting/clear visibility on the Hong Kong MTR station stairways is found to be the major factor of concern, with interest in the environment being of low priority. The proposed LOS standards can be used as a basis for the design and development of pedestrian stairways both in Hong Kong MTR stations and in stations of other Asian cities with similar environments.

This paper focuses on evaluating the role intelligent transportation systems (ITS) are likely to play in alleviating traffic congestion in a developing congested city. Hot Spot Management (HSM) is selected as the ITS application for this study. The various HSM tasks and components are identified, and the detection, verification, and response techniques are discussed. A case study is presented for the introduction of ITS to Lebanon, within the context of local constraints. A simulation-based evaluation of the potential benefits of HSM is conducted using DYNASMART. Various scenarios are tested, with the main parameters being incident (hot spot) location as well as type and severity of incidents. The implication of information provision techniques and market penetration was also considered. The overall network benefits are demonstrated through change in average network trip time and speed. It is concluded that HSM application involving incident detection and response based on local information and communication infrastructure is likely to provide tangible benefits, and that such benefits are robust with respect to expected penetration rates.

Airport leakage refers to the phenomenon where travelers in small, single-airport regions avoid using their local (nearest) airports and prefer to use the more distant but larger metropolitan airports. Past studies of airport choice did not consider airport leakage tendencies of air travelers in single-airport regions, nor considered how the choice probabilities of individual travelers are affected by the goodness or badness of the travelers’ experiences with one or more of the candidate airports. This paper extends the research on airport choice by considering the airport leakage tendencies of travelers in single-airport regions, and by incorporating variables that capture the individuals’ heterogeneity of airport experience. The results indicate that single-airport area travelers are more likely to leak to larger metropolitan airports when their trip purpose is leisure than when it is business, and that travelers are more likely to choose the airports in which they gained good experiences than those which they have never used or had bad experiences.

Load transfer in rigid pavements needs to be appropriately considered for portland cement concrete (PCC) pavement analysis and evaluation. One assumption has been extensively used: that the sum of deflections on two sides of a joint equals the free edge deflection. In this paper, the assumption is theoretically proved to be true when the slabs are in full contact with the base. However, it is also proved that it is generally not true when the slabs are curled up. Therefore, in analysis and evaluation for significantly curled PCC pavements, the assumption should not be used.