Showing papers in "Transportation Research Record in 1975"

Permanent deformation characteristics of subgrade soils due to repeated loading

Abstract: Various procedures are examined for controlling or estimating the contribution of the subgrade to the total permanent deformation that occurs in the pavement structure as a result of repeated traffic loads. The use of layered elastic analysis to estimate the vertical compressive strain at the subgrade surface is suggested as one procedure to control such deformation. A summary of available strain data is included. If these criteria are used for design purposes, the same range in stiffness for the asphalt-bound layer and the same values of Poisson's ration must be used as were used to develop the criteria. Layered elastic analysis is also suggested for estimating the amount of permanent deformation caused by the subgrade. This analysis is based on relationships among permanent strain, applied stress, and number of stress applications based on repeated-load triaxial compression tests; and these relationships are discussed. Data also indicate the importance of stress history effects. Time hardening and strain hardening permit estimates of cumulative loading effects from the results of tests at single stress levels. Although neither method predicts precisely the accumulation of permanent strain under different stress sequences, both bound the measured data and therefore have the potential to assist in the estimation deformation or rutting from cumulative traffic loading.

Aggregate travel demand forecasting from disaggregated behavioral models

Abstract: This paper derives an expression for obtaining aggregate (interzonal) travel forecasts given a probit disaggregate demand model and zonal averages and intrazonal variances of the independent variables. It also derives expressions for the biases in aggregate model calibrations resulting from zonal homogeneity assumptions in the variables. The conditions under which these biases are important are discussed. Expressions are also determined for obtaining consistent, unbiased estimates for both aggregate and disaggregate models that take into account nonhomogeneous zones and practical data limitations.

Significance of cyclic confining stress in repeated-load triaxial testing of granular material

Abstract: A number of research projects have been concerned with determining the nonlinear stress-strain characteristics of granular materials by using repeated-load triaxial tests. Improvements in materials testing equipment have lead to experiments in which the confining stress and the vertical stress were applied cyclically. There is an apparent difference in the resilient Poisson's ration determined under constant and under variable confining stresses. This difference is best explained by considering the behavior of granular materials in terms of volumetric stress-strain and shear stress-strain relationships. By doing this, one can show that Poisson's ratio is a function of the ratio of volumetric strain to shear strain. Resilient strains were investigated separetely from permanent strain because the permanent strain developed depended on the loading history of the sample and because the resilient behavior was not affected by any previous subfailure stress applications. To keep materials testing techniques simple, a constant confining stress equal to the mean value of a cyclic confining stress can be considered to be equal to the cyclic confining stress for determining the resilient modulus and permanent deformation.

Identification of hazardous rural highway locations

Abstract: An effective procedure was developed for identifying hazardous rural highway locations based on accident statistics. Indicators of accident experience that are necessary include the number of fatal accidents, total number of accidents, number of equivalent-property-damage- only accidents, and the nature of the local safety improvement program, local traffic and roadway conditions, and prevailing attitudes toward highway safety. Specific recommendations are given for use of the procedure in Kentucky. Critical accident rates are established by using quality control procedures. In identification of hazardous highway locations, distinction is made between short highway segments (spots) and large segments (sections), and spots are further classified as intersection and nonintersection locations. Intersection spots should include a distance of 0.15 mile (0.24KM) along all approaches; nonintersection spots should be 0.3-mile (0.48-km) floating segments; and sections should be 3-mile (4.8-km) floating segments. Both spots and sections should be classified by highway type and location. The use of 1- and 2-year intervals for accumulating and evaluating accident statistics was found to be desirable.

Capacity of walkways

Abstract: Flow and space standards for walking facilities and their application are focused on. Consistency is shown in a comparison of work done by various researchers on speed, flow, and density relationships. Levels of comfort at different fractions of maximum capacity are defined. The effect of short-term fluctuation of flow, know as platooning, is evaluated and related to average conditions. Levels of service for platooning are postulated based on available space per pedestrian. Key flow rates for defining walkway service levels are 2, 4, 6, and 10 pedestrians/ min/ft (7, 13, 20, and 33 pedestrians/min/m) of walkway width corresponding to 130, 65, 40, and 24 sq ft/pedestrian (12.08, 6.04, 3.72, and 2.23 sq m/pedestrian) respectively.

Role of waiting time, comfort, and convenience in modal choice for work trip

Abstract: This paper is concerned with the development and use of a policy-oriented, disaggregated behavioral choice model for transportation planning problems and emphasizes the impacts of changes in travel comfort, convenience, and waiting times. The econometric method chosen was logit analysis, and, in that the logit model can be derived from demand or choice, we can interpret logit coefficients as trade-off values. The model is based on survey data for commuters' work trips in the Stockholm metropolitan area in 1968 and 1971. It contains choice variables, socioeconomic variables, and transportation policy variables. The most important choice variable is "the use of car for work," which supposedly restricts the possibility for public transit use. The socioeconomic variable is income. The Transportation policy variables are travel time, travel cost, and the chance of getting a seat. A dummy variable technique is applied to the binary-choice approach so that stratification of the choice situation for different types of transit modes within the same model is possible. This allows for differences among the various transit modes in relation to comfort. The survey data are subdivided into two income groups to test the hypothesis that the value of time and comfort depends on the level of income. Results from our research are of particular interest when suggested changes in public transportation are compared with each other or with the do-nothing alternative.

Corrosion testing of bridge decks

Abstract: When the corrosive half-cell potentials on a bridge deck exceed about 10 percent or when corrosion-caused delamination exceeds about 1 percent of the deck area, a chloride analysis generally would not be required because the chloride content is already too great. For the average depth of reinforcing steel, the quantity of chloride apparently needed to cause corrosion was statistically related to the maximum amount at the 95 percent confidence limits of 1.0 lb/ cu yd (0.59 kg/ cu m). The accuracy of chloride determinations was about equal whether the concrete was drilled or cored. Although the half-cell potential of -0.35 volts CSE is indicative of active corrosion, an equipotential contour map is the most reliable means for evaluating the corrosion activity of steel in concrete. After repair of concrete delaminations, the percentage of corrosive potentials decreased by about 50 percent. Repairing concrete delaminations does not prevent or necessarily control corrosion at other locations.

Preloading by vacuum: current prospects

Abstract: The concept of using atmospheric pressure to apply a precompression load for accelerating the consolidation of foundations for embankments constructed on soft clay soils was first described by Kjellman in 1952. The method, although theoretically sound, was impractical then because the plastic sheets that covered the sand filter deteriorated rapidly in field use, and consequently the vacuum could not be easily maintained. Recently, new plastic and fabric materials have been developed that promise to make the Kjellman vacuum preloading method practical. The materials are cheap, strong, and resistant to deterioration by sunlight and weather. Practical applications and several specific advantages of the vacuum method are described, and factors affecting the costs of highway and other preloading construction are given. Depending on the relative costs of the fill materials and the plastic membranes, the vacuum method be significantly cheaper than conventional preloading using sand or gravel surcharge fills.

CORQ-a model for predicting flows and queues in a road corridor

Abstract: A procedure has been developed for predicting the self-assignment of time-varying traffic demands in a network. The procedure's computer program, CORQ, has been used to validate and apply the model in a real corridor. It is intended as a tool to enable the traffic analyst to assess the systemwide effects of any traffic-control strategies proposed for a network as long as the total system's demands remain invariant or at least have a predictable response to the controls. The model has been specialized to give detailed treatment to the critical elements of a corridor that affect traffic flow, capacity, queuing, and delays. It can be used for a form of microanalysis of areas that are about 500 blocks large. For these cases it considers only the major intersections, freeway interchanges, and their surface-street links but gives them a detailed treatment. It can be used for much larger areas if only the freeway network needs to be modeled. Time-varying traffic controls can be simulated. CORQ also can serve as a partial optimization technique by selecting metering rates that fully use the capacity of a merge without queuing on the freeway. CORQ is intended for use in estimating quantitatively the effects of various types of traffic control strategies before a commitment to any specific control schemes and installation of specialized hardware. It can serve as a traffic-management game, and it has been used in training students in the design of traffic-engineering and traffic-control schemes including ramp closure, ramp metering, restriping, and altering traffic-signal splits.

Transverse, Pavement Markings for Speed Control and Accident Reduction

Abstract: Transverse pavement markings were placed ahead of a sharp curve that had a history of high accident rates. Before-and-after studies of speed and accidents were conducted. The markings were placed so that drivers who failed to slow when approaching the curve would see the transverse lines on the pavement at an increasing rate. The spacing of lines was intended to create an illusion of acceleration that would cause the driver to slow. The results indicated that pavement markings can be an effective speed-control measure and reduce accidents. At the single site studied, the obedience of drivers to this type of hazard warning was more effective than signing alone. Further use of this type of marking may be warranted at locations at which excessive speed contributes to accidents. The length or roadway marked in this trial was 247 m (810 ft). Although the striping tape performed satisfactorily, painted lines could be used as an alternative.

Asphalt binder hardening in the michigan test road after 18 years of service

Abstract: Analysis of six binders used in a Michigan test road has given an indication of the mechanism of compositional change and resultant hardening occurring during service. All the binders show the same directional changes in composition, namely a decrease in naphthene aromatics, which convert to polar aromatics and in turn to asphaltenes. This conversion is more pronounced in the top 1/8-in. (3.2-mm) layer than in the underlying 1/4-in. (6.4-mm) layer. The mechanism proposed here clearly explains the increase in softening point, increase in hardness, and loss of ductility. Change in composition and physical properties also accounts for the slight but observable differences in the wear, weathering, and raveling qualities of the different sections. The Michigan test road and its overlays are still in service, although they show considerable reflection and joint cracking. Superficial judgment indicates that two of the test sections show more wear and weathering than the others. Although this is of technical interest, these differences are not large enough to permit quality judgment or selectivity between sources.

Generalized combination method for area traffic control

Abstract: A simple generalization of the British combination method is given for optimizing offsets in synchronized, traffic- signal networks of a general structure. The method then is used in a recursive procedure to determine values for the offsets along each street, the splits of green time at each intersections of the network, and the common cycle time of the controlled area. The signals' cost to travelers is evaluated as the sum of 2 components: one associated with a deterministic traffic-flow model and the other associated with randomness in traffic behavior. The deterministic component is a function of the coordination among the signals in the network and generally increases with cycle length. The stochastic component depends on the expected overflow queue at each traffic light and decreases with cycle length. It is shown that optimal settings are determined at the equilibrium point of minimum total cost resulting from the combined effect of the 2 components.

Relationship of accident patterns to type of intersection control

Abstract: The change in accident patterns accompanying a change in intersection control was investigated. The investigation include a review of previously made studies, an analysis of before and after accident data, and a detailed statistical analysis of a large, specially assembled, nationwide accident data base. Analysis of variance and regression techniques was used to show that the relationship of accident patterns to type of control must be represented by a complex model and that a simple-signal-no-signal division cannot explain changes in accident patterns. A large number of different measures of effectiveness that describe changes in accident patterns were computed and analyzed. Hypothesis testing revealed that, although there was a definite shift in the distribution of accident types, there was no evidence that signalization, by itself, would lead to a significant decrease in net accident-related disutility, especially for traffic signals not warranted by traffic volume. No conclusive evidence was found to justify a general reduction of minimum volume requirements for rural conditions or high-accident locations.

Relationships between roadway geometrics and accidents

Abstract: Statewide average and critical rates of accidents were determined from 1970, 1971, and 1972 Kentucky accident records for each type of rural highway. Accident data, obtained from state police computer tapes, were summarized to give the number of accidents on each highway type as well as information on accident severity, road surface conditions, light conditions, road character, and type of traffic control. Four-lane undivided highways had the highest average accident rate, and parkways (toll roads) had the lowest rate. The severity of accidents was related to types of accidents, highways, and traffic control and to safety belt use. Accidents involving pedestrians were the most severe, and single-vehicle accidents ranked next highest in severity. Excluding accidents at railroad crossings, accidents that occurred on curves had the highest severity index. The use of safety belts was associated with reduced severity.

Driver work load for various turn radii and speeds

Abstract: The need exists for a method by which a highway designer can determine, during the design stage, whether a highway design will demand so much of a driver's attention that there is insufficient time to look for and avoid accidents. One aspect of attentional demand is tracking the lane in curves and tangent sections. A study was done to determine (by use of a secondary task) what percentage of a driver's attention is required to track a lane while various curves are negotiated at various speeds. In addition, data were gathered about how drivers control their lane position. Results indicated that lane tracking in a 17-deg turn demanded 26 percent of the subject's attention at 20 mph (32 km/h) and 42 percent at 40 mph (64 km/h) and that attentional demand in the straightaway remained around 23 percent for speeds from 40 to 80 mph (64 to 129 km/h). Lane-tracking data indicated that the median location was 5 in. (12 cm) to the left of the lane center in straightaways, 7 in. (18 cm) to the left in left turns, and 6 in. (15 cm) to the right in right turns. Distributions of drift distances from these three median locations were also determined.

Asphalt Properties in Relation to Pavement Perfomance

Abstract: Six asphalt cements from different sources were used during 1964 in the construction of the pavements studied and reported in this paper. These asphalt cements ranged in viscosity at 140 F (60.c) from 966 to 2,649 poises (96.6 to 265 Pa-s) and in penetration from 62 to 149 units. Tests have been conducted to determine the properties of the original asphalts, as well as the asphalts recovered from time to time from the pavements in service. The performance of these test pavements was evaluated in 1974 by a team of eight evaluators. Changes in the asphalt properties have been observed to be a hyperbolic function of time. According to this study, viscosity or shear susceptibility of the aging asphalt alone does not, necessarily, indicate the pavement performance. The rate of gain in shear susceptibility relative to increase in viscosity at 77 F (25 C) seems to be one of the major factors affecting pavement performance. Asphalt ductility values, determined at 39.2 F (4.c) before and after pug mill mixing, seem to be consistent with the pavement performance observed so far. Higher ductility values are associated with better pavement performance.

Simulation of an unconditional preemption bus priority system

Abstract: An urban network traffic model has been modified to simulate a bus priority technique that automatically grants a green signal to buses as they approach an intersection. Such a technique could be implemented at individual intersections. Bus routes along 18th and 19th streets in downtown Washington, D.C., were simulated, and traffic data representing the morning peak were used as model input. Repeated simulation runs tested the effect that the bus priority system had on bus and nonbus traffic for combinations of bus headways (from 0.5 to 4 min) and near-side and far-side bus stop locations. The technique substantially improved many aspects of bus operations, including reduction of the mean number of unnecessary stops, and the mean, 90th percentile, and standard deviation of travel time. An improvement of 15 to 20 percent in bus travel time was supported by statistical test. Other vehicles on bus streets also benefited from this type of system. Cross-street traffic was adversely affected by shorter headways, but far-side stops were far superior to near-side stops under those conditions. Under the conditions simulated, the bus priority system would have the least impact on other vehicles in applications with far-side bus stops when headways were 2 min and greater. However, a consideration of passenger movement rather than vehicle movement may indicate that the system should be operated at shorter than optimum headways.

Effects of increased enforcement at urban intersections on driver behavior and safety

Abstract: The study described in this paper was initiated in 1972 in an attempt to define the nature and magnitude of the effects on driver behavior and safety resulting from increased levels of enforcement of traffic laws. A major purpose of the study was to investigate the increased benefits to be obtained from higher enforcement levels to determine how police can be cost effectively employed. The results of the study indicated that visible police presence at an urban intersection can significantly reduce the incidence of traffic violations. This effect appeared to be restricted to the time of actual police presence; it disappeared almost immediately after the police left. Traffic conflicts were recorded as representing a measure of safety, but, although their effects were similar to those on violations, results were not judged significant. Based on effectiveness in reducing violations the most significant improvement occurred in employing a single policeman for a period of 1 h/day. Further increases in effort did not produce appreciable further improvement.

Thermal stresses in concrete bridge superstructures under summer conditions

Abstract: Current design practice for deep concrete bridge superstructures generally ignores the influence of the diurnal heating cycle on the flexural response of members and instead, considers mean temperature effects. A 1-demensional heat-flow analysis is used to study the flexural deformations and stresses that are developed in deep concrete sections as a result of a typical summer heating cycle. Both nonlinear temperature and stress distributions are observed, and nonlinearity increases with member depth. An analysis of 2 typical continous concrete structures indicates stresses exceeding those associated with live load and amounting to 40 percent of the allowable area possible for concrete structures having a depth of more than 4 ft (1.22 m).

Physiological reactions of drivers as indicators of road traffic demand

Abstract: Sixty drivers, all accustomed to a certain make of car, performed test drives along a certain test road. A digital tape recorder was used for real-time recording of the driver's physiological characteristics (electrodermal response, heart rate, and muscle activity), steering, and braking; the vehicle response (accelerations in three directions, velocity, and distance traveled); and traffic events as coded by the experimenter. The characteristics of the test road were measured in the field. Average responses were calculated for the test road, and significant covariations were demonstrated by using the physiological measures as the dependent variable and vehicle behavior on the road as the independent variable. It was also found that the difficulty of a traffic event affects both the driver's brake use and physiological responses. Stress- inducing road characteristics are downhill grades and short sight distances. It is suggested that the driver's capacity to process information varies flexibly as task demand changes. Sudden increases in task demand can be leveled out by modeling the road environment, and this makes the driver more competent at dealing with hazardous situations.

Effects of design alternatives on quality of service at signalized diamond interchanges

Abstract: This paper examines the effects of minimum phase length and variations in the spatial arangement of ramp intersections on the capacity of diamond interchanges operated with 4-phase-overlap signalization. The introduction of practical minimum constraints on phase lenghts can significantly alter the performance characteristics of this type of interchange. This paper also illustrates a method by which interchange design can be assessed in terms of quality-of-service measures. A computer program, written in FORTRAN IV, was developed to speed up the analysis. Examination of some typical cases illustrates that an efficient design can be selected if one uses the program for a given set of minimum green-phase lengths and traffic demands.

Capacity of signalized intersections

Abstract: Standardized methods for estimating capacity at signalized intersections have been sought for at least 25 years. The publication by the Bureau of Public Roads of the 1950 Highway Capacity Manual was the first extensive effort made toward this objective. In 1960, W.R. Bellis, of the New Jersey Department of Transportation, developed a more simplified technique. The results of the research discussed in this paper indicate that the techniques in the Highway Research Boards 1965 Highway Capacity Manual yield greater than 20 percent error in estimating the through capacity of the approach to a signalized intersection for at least half the locations studied. When the Bellis technique was used, less than 20 percent of the locations showed this error. Revisions were made to techniques in the 1965 Highway Capacity Manual, and 20 percent error then was found in only 25 percent of the locations studied. It was concluded that measuring the capacity of an approach in the field is preferable to estimating capacity by using the 1965 Highway Capacity Manual. A method of determining capacity from field measurements is described briefly in the paper.

Assessment of pedestrian attitudes and behavior in suburban environments

Abstract: Suburban area pedestrianism was examined from the points of view of the walking and nonwalking public. Nine case studies were conducted to determine the role of walking as an exclusive mode of travel. The sites examined comprised the 3 major types of pedestrian facilities: overpasses, tunnels, and at-grade crossings. Locations where new pedestrian facilities are anticipated also were examined. In each case, linkages between land uses were established to define reasons for local travel. The data then were analyzed to show how pedestrian facilities act to sustain the linkages. Various pedestrian characteristics were found to be related to walking activity. For example, age has a direct bearing on walking behavior, and children constitute the largest walking group. Acceptable walking distance of up to 0.25 mile (0.4 km) were given for adults. Distances of up to 1 mile (1.6 km), however, offer little impedance to children. Along with distance, fear of attack is a primary impedance to potential adult walkers, especially women. Overpasses were cited as the most desirable pedestrian accommodation to bypass traffic. The public showed little enthusiasm for tunnels because of the mischief they attract. People have also shown that, if the reason exists, they will cross heavy traffic to travel by foot. The results of this study given general principles for successful pedestrian planning in suburban areas, and they support the idea of combined pedestrian and bicycle ways.

Comparison of effectiveness of various measures of socioeconomic status in models of transportation behavior

Abstract: Socioeconomic status is often theorized to be associated with variables measuring transportation behavior, and, income is the most frequently used measure of socioeconomic status in most transportation studies. However, sociologists have long hypothesized that other measures of socioeconomic status, e.g., education or occupation, are more appropriate describers of individuals or households in certain situations. The purpose of this paper is to decide on empirical grounds whether income is more appropriate than some of the other indicators of socioeconomic status in transportation modeling contexts. Data was from a stratified probability sample of 223 households in the Santa Monica-west Los Angeles, California, area. Income of the household, education of the respondent, and occupations of the household head and the respondent were the indicators of socioeconomic status. Classes of variables measuring transportation behavior (dependent variables) were trip frequencies and indicators of modal selection. Dependent variables were used in models that included the indicators of socioeconomic status as independent variables and in simple two-variable relationships involving these indicators. Regression analysis, correlation analysis, logic analysis, and simple tests of the significance of differences in means showed that at least one of the other indicators was more strongly associated with the dependent variables in almost all cases.

Effect of certain roadway characteristics on accident rates for two-lane, two-way roads in connecticut (abridgment)

Abstract: This study identified and defined which roadway elements are statistically correlated with accident occurence and evaluated the relative merit of each element as an index of accident prediction. Of the three principal factors associated with accidents, the vehicle, the driver, and the roadway, this paper considers contribution of the roadway. Four selected geometric elements, roadway width, horizontal curvature, vertical clearance, and restricted sight distance were rated for adequacy, and these ratings were then correlated with accident rates. Multiple linear regression analyses were performed to examine these relationships. The resulting correlation coefficients were quite small. Of the four geometric characteristics considered, restricted sight distance and horizontal curvature appear to have some effect on accident rates and vertical clearance appears to have no effect.

Case studies of variations in subgrade moisture and temperature under road pavements in virginia

Abstract: Changes in moisture under uncovered ground and in the subgrades of pavements were evaluated. The pavements ranged from new to about 10 years old. Moisture content was determined by a nuclear probe to determine moisture depth. The findings were as follows: (a) the higher the compaction and dry density of the subgrade soil were, the lower the moisture content would be; (b) subgrade moisture content increased sharply from the beginning to the end of construction; (c) for 1 or 2 years from the date of the subgrade construction, moisture content increased because of precipitation and after this time the rate of increase in moisture decreased; and (d) after about 10 years, there was little increase in the subgrade moisture content.

Probabilistic approach to prediction of consolidation settlement

Abstract: The method of derived distributions is used to develop a probabilistic model for predicting the total settlement in a compressible clay layer in terms of uncertain soil compressibility and loads. The settlement ratio (total settlement divided by thickness of compressible layer) is a function of two independent random variables (compressibility factor and load factor). The compressibility factor is a function of two dependent random variables (compression index and initial void ratio), and the load factor is a function of two independent random variables (total stress at the midheight layer and the preconsolidation stress). The compressibility factor can be described by a normal distribution, and the load factor by a log-normal distribution. The derived distribution of the settlement ratio is also well approximated by a log-normal distribution that approaches a normal distribution as the number of soil samples taken for the settlement prediction increases. Graphs are developed to estimate the settlement ratio parameters in terms of the average dry density of the soil. The effect of the number of samples and the vertical and horizontal correlation on the density function of the settlement ratio is also evaluated.

Temperature distributions in asphaltic concrete pavements

Abstract: The straight-line relationship derived from Maryland data between temperatures at a given depth and the surface temperatures plus 5-day average air temperatures is as valid for upper New York State and Arizona as for Maryland. The main differences were in the annual ranges and annual mean temperatures. The concept for estimating pavement temperature distributions appears to be valid and may be used with confidence for estimating pavement temperatures at all latitudes and longitudes.

Improved framework for predicting permanent deformation in asphalt layers

Abstract: When permanent deformation in asphalt pavements is predicted by elastic analysis and repeated-load triaxial testing, problems arise in the tension zone because of tensile stress in both horizontal directions. This stress situation cannot be directly reproduced in the triaxial test. An approach is suggested to deal with this problem in particular and with pavement materials characterization in general. It recognizes that strains developing in any particulate material depend on the combination of mean normal stress and octahedral shear stress. These stress invariants are functions of the principal stresses but are independent of their directions. Triaxial tests can be more flexibly used by reproducing the appropriate values of these stress invariants rather than the in situ principal stresses. Measurement of vertical and lateral strains during the test permits the evaluation of corresponding strain invariants that can be used to calculate the in situ vertical strain, which is of interest in rut depth prediction. Elastic analysis indicates that the suggested approach should lead to better predictions of permanent deformation in high temperatures and thick layers. The very high tensile stresses associated with lower temperatures and thinner layers still, however, present a problem because only one tensile stress can be applied in the triaxial test.

Pavement cracking in west texas due to freeze-thaw cycling

Abstract: Freeze-thaw contraction of the base course material used in west Texas is considered an important element in pavement deterioration. Samples from two compactive efforts were frozen in a biaxial closed system. Suction and temperature within the samples were monitored and volume changes after each freeze-thaw period were recorded. Coefficients of thermal activity were calculated from the dimension measurements. These coefficients showed a relationship with the as-compacted total soil moisture suction, which was similar for all materials. Finite element studies of the thermal strains that develop in a typical pavement showed that the thermally induced tensile stresses in the base course are far in excess of typical tensile strengths for initially intact pavements. The surface course did not develop excessive stress levels. Freeze-thaw cycling produced plastic deformations in all samples, and the permanent expansion or contraction was related to the as-compacted total soil moisture suction. These permanent deformations from freeze-thaw cycling imparted a residual tensile stress to the asphalt concrete. During a freeze, suction in the sample showed a marked increase, often 10 to 20 times the initial value. The suction then dropped below the initial value during the thaw cycle. This drop was consistent regardless of the thermal activity of plastic deformation. This indicated a reorganization of the moisture in the sample, which may be related to strength losses caused by freeze-thaw cycling. The data in this study give new insight into the mechanism of freeze-thaw in pavement deterioration.