Shear stresses at the interface between an existing concrete pavement and an overlay are calculated using the finite‐element method for different loading conditions. The effects of vertical wheel loads, temperature loading, and wheel braking forces are considered. Perfect bonding between the overlay and the pavement is assumed. The pavement‐overlay slab is modeled using thin plate elements for calculating the stresses due to the vertical wheel load and temperature gradient. In analysis for stresses due to wheel braking loads, the slab is modeled with solid elements. The results are checked against Cerrutti's closed‐form solution in the case of horizontal wheel braking. The computed shear stresses at the pavement‐overlay interface for typical values of pavement and overlay thicknesses, wheel loads, and thermal gradients are compared to reported values of shear strength of laboratory‐prepared overlaid specimens. The shear stresses at the interface are found to be small in relation to the interfacial bond strength of laboratory‐prepared overlaid specimens. The findings suggest that debonding in overlay construction in the field is likely to be caused by stress concentrations due to local defects.

This paper describes a reliability model developed for continuously reinforced concrete pavements (CRCPs) for the Texas Department of Transportation. The model predicts the probability that a CRCP section with a certain amount of distress manifestations will last at least a certain number of equivalent‐single‐axle‐load (ESAL) applications. An existent Texas CRCP distress index was used to quantify the pavement condition, and accurate predictions of ESALs to failure were obtained for each reliability level using a CRCP database containing more than 80% of nonfailed sections. While conventional methods for model calibration would preclude use of more than 80% of test sections in the database, the approach used here takes into account the data provided by nonfailed sections, maximizing the amount of information extracted from the data, and allowing timely development of an operational pavement management system to comply with the 1991 Intermodal Surface Transportation Act. An example of the model application in pavement management is presented, and the practical advantages of the CRCP model over traditional models are discussed.

Gravelly subgrade materials are frequently evaluated on the basis of laboratory testing on material passing the number 4 sieve size due to difficulties in obtaining representative samples and because laboratory testing of soils containing rock is more difficult or expensive. When the large aggregate is not considered in the evaluation process, it is quite possible to discard a material as being inappropriate as subgrade material when in fact it may be quite suitable. For example, the presence of rock or gravel materials may have an ameliorating effect for clayey soils having potential for expansion upon wetting. The effect of large aggregate on the moisture sensitivity of subgrade materials are reviewed. It is more difficult to establish field specifications and to conduct field inspections for compaction of subgrades containing large aggregate. The potential pitfalls in obtaining the desired relative compaction in the field are discussed. The various comonly used techniques in writing field specifications for compaction of materials containing rock or gravel are reviewed.

An innovative method of applying a spatial autocorrelation function to analyze pavement image data is presented in this paper. One of the major advantages of using a spatial autocorrelation function is its capability of suppressing the noise. By calculating the autocorrelation function of the pavement image, we can measure direction and area of the crack under the presence of background noise. An algorithm is developed and programmed using C language to identify crack type and to measure crack density automatically. The algorithm is illustrated using artificially prepared crack images. Randomly selected sample video images of real cracks are used to demonstrate the accuracy of the proposed automated crack‐imaging procedure. Based on the limited set of data, it is concluded that the proposed automated procedure can identify crack type and density with a reasonable accuracy. It is proposed that the crack‐density measure could be used as a combined index of various crack types for managing pavements at the network level.

The ability to accurately evaluate roadside hazards is very important to highway safety officials and researchers, who are concerned with reducing the frequency, severity, and ultimately, the cost of “run‐off‐the‐road” highway accidents. The roadside environment in the province of British Columbia, Canada, contains many hazards to motorists due to severe topographical characteristics, including steep embankment slopes and numerous roadside features that would cause harm if struck by a vehicle. This paper describes the need to accurately evaluate hazardous roadside locations by outlining the limitations in the existing procedures and summarizing the effectiveness of a computer simulation model, the roadside‐hazard—simulation model: version 9. The model contains dynamic vehicle simulation with traffic and roadway conditions to estimate the effectiveness of a variety of countermeasures. These countermeasures can then be ranked by economic evaluation criteria, such as benefit/cost ratio and cost‐effectiveness.

Toll collection on freeway main lines can have serious repercussions on freeway operation and management. There are currently no suitable methodologies for level‐of‐service analysis of main‐line toll plazas. To bridge this gap in the state of the art of level‐of‐service analysis of highway facilities, a methodology is developed. This methodology relies heavily on a computer simulation model referred to as toll‐plaza—simulation model. The reliance on computer simulation reflects a recognition of the limitations of analytical models and the popularity and computing power of personal computers. The operating characteristics of toll plazas are examined through field observation and computer simulation. The performance of a toll gate can be significantly affected by a number of factors such as service capacity, vehicle arrival pattern, number of available gates, and driver behavior. A stable performance can generally be expected if the average queue length at a toll gate does not exceed three vehicles. An average queue length of more than 10 vehicles represents a rather unstable and undesirable operation. Average queue length and average time spent in a toll‐collection system are used as the measures of effectiveness to classify quality of service into six levels. The essential features of the recommended methodology are presented.

Variable message signs are used as part of freeway management systems to provide drivers with real‐time information on roadway and traffic conditions. Fiber‐optics and light emitting diodes are two emerging technologies currently being marketed for use as variable message signs. As these technologies become increasingly used in freeway management systems, it is important that drivers be able to read and to comprehend their messages. This paper presents data on legibility distance, target value, and viewing comfort measured by observers as part of a comprehensive human‐factors study of two light emitting diode and four shuttered fiber‐optic variable message signs in Phoenix, Ariz. Data for these parameters are given for an older and a younger group of observers. The presentation of these data leads to a discussion on design considerations for fiber‐optic and light emitting diode variable message signs.

Walking and bicycling are the two modes predominantly used for travel in urban areas of developing countries, and the location of transport‐related facilities in urban areas thus is influenced by the characteristics of these modes. The promotion of trips by these nonmotorized modes will also help, to a significant extent, in energy conservation and environmental protection. Herein, the home‐based walking and bicycling trips of Tiruchirapalli, India are analyzed with respect to trip length, and the influential variables like age, sex, occupation, trip purpose, and time of day of travel. Significant variations in trip lengths by walk and bicycle were found to exist among trip makers of different categories. As walking and bicycling modes cannot be used for longer trips, it is necessary to determine the acceptable trip lengths by the two modes. The acceptable trip length for these modes was found by fitting polynomials to the trip‐length distributions. Use of probability distributions for determining the acceptable trip length has also been illustrated in selected cases.

An optical inspection system has been developed to detect the presence of defects on the surface of rails. The system classifies each 6 in. (15 cm) length of railhead as defective or nondefective and generates large quantities of disaggregate, sequential condition data. Defective rail surfaces can then be corrected by grinding the surface of the rail. However, this requires that condition data be aggregated to a level suitable for making maintenance decisions, and that prior recognition be given to practical constraints such as adjusting minimum grinding length to the configuration of the particular grinding machine. Data‐aggregation procedures range from rule‐based techniques to mathematical optimization methods. This paper reviews these aggregation techniques and, consequently, formulates the grinding problem as a set‐packing integer programming formulation. Two heuristic solution methods are proposed to solve a set‐packing problem of high dimension resulting from a large number of feasible packs for rail‐surface‐condition data. These methods effectively moderate the computational intensiveness and time complexity associated with using existing procedures.

The principles of temperature‐related stresses are discussed. Statistical evidence of temperature effects on water‐main breaks are also presented from the Washington (D.C.) Suburban Sanitary Commission's experience. A strong correlation was found between water temperature and main break activity. The temperature drop was shown to be a significant factor. A new low in the water temperature resulted in a sharp increase in the number of main breaks. The breaks were mostly circular and occurred on grey cast‐iron pipes ranging in size from 76 mm (3 in.) to 203 mm (8 in.) A failure mechanism is presented to explain the complex nature of temperature related main breaks. The mechanisms explains why break activity is not uniquely related to the temperature. It also shows how different break activities may occur under similar temperature‐drop conditions. The complex nature of temperature‐related water‐main breaks does not lend itself to a simple forecasting model. However, a practical and simple procedure is presented that may be used to provide advanced warning of high break activity. This information helps the utility manager to prepare for the heavy repair demand on the maintenance crew.

Vehicles that run off the road and then slide sideways into fixed objects along the roadside are an important accident scenario that has been often overlooked in developing roadside hardware. This paper combines the results of the 1991 side‐impact crash testing program conducted at the Federal Outdoor Impact Laboratory (FOIL) with those of previous side impact crash tests on energy absorbing, slipbase and transformer base poles to develop new injury measures related to the thoracic and head body regions. Regression models that link the crash test performance to the probability of occupant injury in the field are presented. These models predict the TTI and the HIC using vehicle‐based observable parameters that can be measured in crash tests. The predicted TTI and HIC can then be used to estimate the probability of injury based on injury distributions developed in human tolerance research. These vehicle‐based criteria, while preliminary, demonstrate a method that could be used to hypothesize about the survivability of similar real‐world collisions.