Capacity analysis is an essential task in the planning and design of signalized intersections. This task becomes difficult to perform satisfactorily when shared permissive left‐turn lanes are present. A shared permissive left‐turn lane allows opposed left‐turn vehicles and vehicles of other directional movements to proceed into the intersection when signal operation enters a permissive left‐turn phase. Because the vehicular movement in such a lane during a green interval may not be continuous, modeling the saturation flow and capacity of a shared left‐turn lane is a complex matter. Existing models are inadequate. To address this problem, an improved model is developed. This model provides logical explanations of the causal relationships between the capactiy, as well as ther saturation flow, of a shared left‐turn lane and a number of governing variables. The governing variables include number of opposing lanes, opposing flow rate, proportion of left turns in opposing lanes, proportion of left turns in shared lane, flow rate in the lane adjacent to the shared lane, proportion of opposing vehicles arriving in red interval, cycle length, green interval, and signal change interval.

The single‐point urban interchange (SPUI) is a relatively new type of diamond interchange. It is claimed to offer improved operational efficiency, improved safety, and reduced right‐of‐way requirements over other interchange forms. This paper addresses the area of operational efficiency by focusing on the SPUI's change interval requirements and the implications of these requirements on the amount of lost time incurred at the end of the signal phase. Values of end lost time are calculated for the SPUI and compared to those of a typical, high‐type at‐grade intersection (AGI). End lost time calculations for the SPUIs and AGIs indicated that the SPUI signal phases have longer end lost times than do the AGI phases. In particular, the SPUI through phase was found to have 1.5‐2.5 sec more end lost time than the AGI through phase. Similarly, the SPUI left‐turn phase was found to have about 1.0‐2.0 sec more end lost time than the AGI left‐turn phase.

This paper examines statistics of truck overloads on highways. An overload is defined as a load that exceeds the legal truckload limit. The overload statistics depend on truck types; each is specified by the number of axles. The truckload spectra examined in this paper reveal that overloads generally appear with a distinctly different pattern than that in lower load levels. This is especially true among trucks with five or more axles. To derive a theoretical probability distribution model to represent different patterns in a load spectrum, mixed distribution models are introduced in this paper. A mixed distribution is made of two different functions, each representing one of the different patterns appearing in the load spectrum. These functions are linearly combined and adjusted to represent the overloads and all other loads statistics properly. Using the statistics of overloads, along with a damage estimation model, one can determine to what extent overloads are responsible for damage done to bridges and highways. The probability of occurrence of specific truck weights exceeding the legal load limit can be used to estimate the frequency of occurrence of heavier loads in transportation facilities and thus determine the damage potentials of overloads. This information can be used along with routine engineering analyses that many pertinent state agencies conduct when issuing truck‐overload permits.

John F. Kennedy (JFK) International Airport is one of the largest and busiest airports in the world. Effective maintenance and management of JFK's extensive network of runway, taxiway, and other airfield pavements presents a major engineering challenge. To accomplish this, the Integrated Airport Management System (IAPMS) has been developed and implemented at JFK. IAPMS couples state‐of‐the‐art pavement engineering methods with powerful information management technology to provide data base management, pavement engineering analysis, and forecasting tools for airfield pavement maintenance management. The basic components of IAPMS and the steps involved in the implementation of IAPMS at JFK are outlined. An example application of IAPMS to hypothetical but typical maintenance management questions at JFK is also provided.

One of the innovative approaches for maintaining and rehabilitating the nation's highways is to develop and implement some form of pavement management system (PMS). This paper documents results of a survey on PMS use in the United States. In addition, a simple method for a PMS based on priority ranking is presented. The model uses the theory of fuzzy sets to process the information obtained from a typical pavement condition survey. An index, called unified pavement distress index (UPDI), is defined and used to measure the pavement distress condition. The new approach is presented in a few key elements: guidelines for rating of six types of distresses, weights among the different types of distresses, fuzzy‐set representations of the linguistic grades and fuzzy mathematics, and the definition of UPDI and its use in a pavement data base. An example is presented to show how the new approach can be employed to analyze data bases generated from a pavement condition survey. While the proposed approach has shown its potential in the example application, more positive feedbacks from large‐scale field tests are needed to demonstrate its reliability and ease of use.

This paper presents work towards the use of histogram‐based machine vision for the automated sensing of unprepared cracks in highway pavement. Machine vision is being developed for purposes of identifying and locating cracks in the size range from 1/8 to 1 in. (3–25 mm) in width in both asphalt concrete (AC) and portland cement concrete (PCC) pavements. The machine vision being developed is intended to work in real time in an automated crack‐sealing machine that will operate at approximately 2 mph. The method is based on segmenting the pavement image into a grid of tiles, and then representing each tile's properties by histogram‐based parameters. Comparison to a localized set of tiles provides information of crack existence and direction. This paper presents preliminary results showing the capability of the approach to find unprepared cracks in real pavements, and additionally, remaining work that will lead to its real‐time implementation is discussed.

The low‐speed cornering of large trucks on urban streets and intersections is a major problem in terms of public safety and traffic congestion. These problems can be alleviated in two manners: (1) Modify the roadway dimensions to allow large vehicles to pass more easily; or (2) modify the size or maneuverability of the large trucks. This paper presents a methodology for the geometric design of articulated vehicle‐roadway systems for optimum low‐speed maneuverability. It is recognized that the highway and vehicle dimensions are inherently linked, and an optimization problem is formulated to achieve the largest possible truck passing through a corner in a dimensionless manner. Such an approach yields optimum truck dimensions in terms of road width. Tractor‐semitrailers moving both forward and backward, as well as tractor‐tandem trailer combinations moving forward, are considered. This paper shows the large improvement in maneuverability through the addition of trailer rear‐wheel steering. In addition to large trucks on the road, this paper can have an impact on the design of two other types of vehicles, those being internal transport systems, such as material‐handling systems in manufacturing facilities, in which space requirements must be minimized but high‐speed performance is rarely of concern, and low‐speed highway‐maintenance machinery, which must operate on a full‐lane width with minimal effect on traffic in adjacent lanes.

As vehicle weight and dimension (VWD) regulations governing the Canadian trucking industry are relaxed, the need to understand the competitive relationship between trucking and the nation's railways becomes acute. The 1990s will see the highway freight industry adapt to larger allowable vehicle weights and dimensions, strengthening its competitive position in the freight service marketplace. This paper predicts the impacts of trucking weights and dimensions reform on the railway industry in Canada. Commodity sections moved by the two main modes, rail and truck, are studied. The annual tonnage of freight for the four. largest commodity sections are identified, where the competition between the railway and trucking industries is very high.

The national and western vehicle weight and dimension regulations agreements and the Roads and Transportation Association of Canada report entitled Economics of Truck Sizes and Weights in Canada, as well as the writers' recent research to model Canadian interprovincial freight movement, are applied. The impacts on the rail transportation industry, including the necessary improvements in order to retain its existing market share, the link‐by‐link railway revenue loss for each freight section, and the total loss in railway revenue, are presented.