An analysis of data of the past few decades from cities around the world indicates that history is repeating itself. Although there are significant differences in socioeconomic and technological characteristics among these cities, a remarkable similarity exists in trends in urban transportation. The current growth in the use of automobiles in many cities of developing countries follows similar trends experienced in the United States and other developed countries several decades earlier. Even though there is much awareness and knowledge about sustainability, private vehicle ownership, and use continue to grow at an increasing pace with rising personal incomes and desires to experience faster and more reliable transportation technology. Urban density, expressed in number of people and/or jobs per unit of land, is the key indicator of the level of automobile ownership and use, and of associated parameters of sustainability. As personal incomes rise, choice of residential and job location increases, causing a decrease in urban density and affecting the relative use of private transportation and public transit. There are policy options related to land use, pricing, and technological factors that can have far reaching influence on the long-term sustainability of urban-transportation systems around the world. The basic implication of the analysis is that urban-transportation sustainability can be greatly enhanced if there are profound changes in urban structures and activities that can slow or reverse the growth in the use of private automobiles and can make transit and other modes attractive and viable.

Linear and nonlinear multivariate statistical analyses are applied to determine how the types of accidents that occur on heavily used freeways in Southern California are related both to the flow of traffic and to weather and ambient lighting conditions. Traffic flow is measured in terms of time series of 30-s observations from inductive loop detectors in the vicinity of the accident prior to the time of its occurrence. Results indicate that the type of collision is strongly related to median traffic speed and to temporal variations in speed in the left and interior lanes. Hit-object collisions and collisions involving multiple vehicles that are associated with lane-change maneuvers are more likely to occur on wet roads, while rear-end collisions are more likely to occur on dry roads during daylight. Controlling for weather and lighting conditions, there is evidence that accident severity is influenced more by volume than by speed.

This paper examines how different price elasticities of travel demand would impact traffic on a toll road with a time-of-day variable toll rate. Price elasticities were derived from data collected on a pair of bridges that currently offer tolls that vary by time of day. Both aggregate traffic data and disaggregate driver data were used to determine a range of probable elasticities. The aggregate method applied the short run price elasticities observed at the operational bridges to a hypothetical toll road. To determine disaggregate elasticity rates, discrete choice models of a driver’s willingness to alter his or her time of travel due to the variable toll were estimated using survey data. Using these models, and varying the socioeconomic and commute characteristics of drivers on the hypothetical toll road, it was possible to determine the impact of different price elasticities on the flow of traffic. Elasticities from −0.076 to −0.15 caused travel times to improve by 8.8 to 13.3%, respectively.

Incidents, defined as unplanned events that temporarily reduce roadway capacity, contribute significantly to urban freeway congestion. Transportation agencies have developed incident management programs in order to support the effective identification and response to incidents. An important element of an effective incident management program is the ability to accurately estimate the freeway capacity remaining following an incident. The objective of this research was to characterize urban freeway capacity reduction resulting from traffic accidents using a large set of traffic flow and accident data. Traffic accidents, a subcategory of incidents, were investigated since they, in particular, result in significant urban freeway congestion due to their frequency and generally substantial reduction of capacity. The results of this effort lead to the following conclusions: (1) Accidents significantly reduce remaining capacity on freeway segments, well beyond the physical blockage of lanes. This research found that an accident blocking one of three freeway lanes resulted in a mean capacity reduction of 63%, while an accident blocking two of three freeway lanes resulted in a mean capacity reduction of 77%; and (2) There is evidence to suggest that accident capacity reduction is best modeled as a random variable, not a deterministic value. The results of this research indicate that the beta distribution provides a good representation of accident capacity reduction for one or two lanes of three lanes blocked.

Under intelligent transportation systems, dynamic route guidance systems (DRG) provide routing information to motorists based on current traffic conditions on a network. Not enough attention, however, has been given to the impact of such dynamic routing decisions on network safety in terms of the predicted number of accidents. The objectives of this paper are to investigate the variation of network-wide accidents caused by traffic redistribution subject to various levels of DRG market penetration, and to examine the potential of a new safety-enhanced route guidance system. A microsimulation model was developed and integrated with a set of accident prediction models for links and intersections. Accident estimates were plotted against time to produce an accident profile that could describe the change of accident occurrence over a time period. Accident profiles, together with average travel time, were used to explain the relationships between DRG market penetration and the number of network-wide accidents. The integrated simulation model was also applied to enhance DRG by suggesting routes with the fewest estimated accidents and hence making route guidance safety conscious.

At signalized intersections, rear-end accidents are frequently the predominant accident type. These accidents result from the combination lead-vehicle deceleration and the ineffective response of the following vehicle’s driver to this deceleration. This paper mathematically represents this process, by expressing accident probability as the product of the probability of the lead vehicle decelerating and the probability of the driver in the following failing to respond in time to avoid a collision. Using this premise, a model of rear-end accident probabilities is estimated using information on traffic flow, traffic regulations, roadway geometrics, and human factors from four-legged signalized intersections in Tokyo, Japan. Estimation findings provide some important preliminary evidence for the development of countermeasures to reduce the frequency of rear-end accidents at signalized intersections.

Improvements to road safety have become a high priority for road authorities due to increasing public awareness and concern of the high social and economic costs of collisions. However, satisfying this priority in an environment of limited budgets and growing fiscal constraints is difficult. It is therefore important to ensure that the funding available for road safety improvements is efficiently utilized. In an attempt to maximize the overall road safety benefits, safety professionals usually invoke a process to evaluate the cost effectiveness of road safety projects. Road safety benefits are normally determined using collision reduction factors (CRFs) that are reported in the road safety literature. However, the results from many previous safety studies are unreliable due to the inability to apply the CRFs to all conditions and because many safety studies suffer from problems with the evaluation methodology and accommodating the random nature of collisions. To resolve these problems, safety analysis software known as the information system for estimating crash reductions (ISECR) has been developed. Information system for estimating crash reductions is an intelligent database that uses a case-based reasoning approach to compile the results from previous road safety research. Information system for estimating crash reductions evaluates the applicability of the results by accounting for site-specific characteristics and the study methodology by assigning a quality score. The system determines the expected CRFs and the range and reliability associated with a safety improvement at a specific location. The evolution of ISECR, a description of current and future enhancements, and the applications for this road safety-engineering tool are the subjects of this paper.

Timing plans for coordinated signals are developed online using real-time traffic data collected by detectors or offline using traffic data previously collected but is representative of the period in which the timing plan is to be implemented. The timing plans developed using offline techniques are generally known as time-of-day (TOD) timing plans as they are generally implemented during a specific time of the day. One of the downsides of the TOD timing technique is the handling of coordination parameters—defined by cycle length, phase split, and offset—when one plan is transitioning to the next plan. This paper presents a methodology to optimize traffic flow during the transition period. The methodology, based on dynamic quadratic optimization, achieves synchronization of coordination parameters through an optimum number of cycles and an optimum number of increments (or decrements) of the coordination parameters. The proposed transition period optimization method has the advantage that the user does not need to specify minimum and maximum cycle lengths in the optimization process, as is the case with current methods. Preliminary simulation results that compared the proposed methodology to transition methods embedded in CORSIM showed that it has the potential of reducing queue delay, particularly on minor street approaches. The delays on major street approaches were comparable and similar in both scenarios in which traffic volumes were increasing or decreasing between the succeeding plans. Additional simulation runs involving various scenarios of geometric, traffic, and signalization conditions as well as field evaluation are needed before the efficacy of this method over current methods used in practice can be ascertained.

The perception of the driver of the road features ahead is an important human factor that can considerably affect traffic safety and design consistency, and should be addressed in road design. An erroneous perception of the road can lead to actions that may compromise traffic safety. Previous studies have shown that combined horizontal and vertical alignments can cause a wrong perception of the horizontal curvature. In this paper, the hypothesis that the perception of the driver of the horizontal curvature is affected by the overlapping vertical alignment is examined analytically. Computer animation was selected as a three-dimensional presentation method of the road perspective, and was found to produce a realistic view of the road. A sample of drivers was interviewed to determine the radius of a horizontal curve on a level grade that would look equal to a radius of a horizontal curve overlapping with a vertical curve. The statistical analysis showed that the horizontal curvature looked consistently sharper when it overlapped with a crest curve and consistently flatter when it overlaps with a sag curve. Field measurements of operating speed profiles on a selected sample of combined alignments confirmed that, for the selected sample of alignments, driver behavior on horizontal curves depended on the overlapping vertical curve rather than the vertical grade of the approach tangent.

The climbing lane is an effective means by which to increase roadway capacity, improve safety, and provide smooth traffic operation on mountainous and rolling terrains where significant trucking prevails. Current critical length design guides for the climbing lane in the American Association of State Highway and Transportation Officials (AASHTO) Green Book is based on truck speed profile charts derived using the design standard of the weight-to-power ratio equal to 120 kg/kW (200 lb/hp). For locations where a significant mix of larger and heavier trucks with more axial loads exists, AASHTO suggests one apply a more representative weight-to-power ratio but gives no specific computational procedure other than a cautionary statement. This study proposes a well-defined approach and formulation to obtain truck speed profiles, based on the nominal dynamic, kinematic, and operating characteristics of trucks on grades. The design controls that regulate the resultant speed profiles include not only the weight-to-power ratio and the grade used in the current AASHTO manual, but also the design engine power of trucks (or the corresponding design load). The formulations, design charts, and tables derived from the design standards consistent with prevailing truck manufacturing specification allow designers to deduce the appropriate critical length for the climbing lane when significant deviation is found between the prevalent truck weight-to-power ratio and the current design standard. For practical design purposes, a tractable approximation model of reasonable accuracy that is suitable for manual calculation is also proposed, thus providing a feasible alternative to the look-up design chart currently employed by AASHTO.

In the design of skid resistant asphalt pavements, it is a common practice in pavement engineering to perform laboratory tests to ensure that the paving aggregate has the required frictional resistance and wheel-polishing resistance, and to specify a minimum surface texture depth of the completed pavement to provide adequate surface drainage for safe travel in wet weather. These controls, however, may not be adequate for all types of pavement construction. For instance, field experience in Singapore indicated that aggregate spacing, or gap width between aggregates, had important effects on the skid resistance of asphalt pavements. This paper describes a laboratory study to examine the effect of aggregate gap width on frictional resistance of laboratory prepared specimens. Aggregate gaps ranging from 2 to 10 mm were studied. The 2 mm gap represents that of a dense graded mix, while 10 mm gaps are found in a typical porous asphalt mixture. The British pendulum tester was adopted for the experimental evaluation of frictional resistance. The laboratory test results confirmed the effect of aggregate spacing as observed in the field. Further experimental tests using laboratory fabricated portland cement specimens indicated that the area of the contact surface, as well as the number of gaps within the test area have significant effect on the measured frictional resistance. There is a need for pavement engineers to examine this effect in the asphalt pavement mix design process to ensure that adequate skid resistance will be achieved in actual construction.

The deterioration of Portland cement concrete pavement is most often due to intrusion of water into the pavement system as well as due to inferior performance of the transverse joints. The infiltration of surface runoff most commonly happens at the transverse joints and cracks. This problem could be solved by eliminating transverse joints and constricting the cracking capability of the pavement by applying an external force to the pavement in the form of posttensioning. The posttension stands are arranged diagonally resulting in cross tensioned concrete pavement (CTCP). The advancement of posttensioning products and procedures over the last 20 years has made this a fairly simple and inexpensive procedure. A reduction in slab thickness and elimination of the need for transverse joints can offset the cost of the posttensioning hardware and process. However, many new design challenges have arisen as a result of the skewing of the posttension strands in CTCP. The edge stresses of CTCP are addressed in this paper. Potential problem areas in the vicinity of the edge were investigated using the finite element method and possible solutions are discussed.

To avoid cumbersome traditional techniques for pavement subgrade evaluation such as the California bearing ratio and the plate loading test, several nondestructive tests (NDT) as well as suitable analysis processes have been introduced to assess the properties, the structural condition, the residual life, and the possible need for improvement of pavement soils. This paper deals with the implementation of the falling weight deflectometer (FWD), one of the most popular NDT techniques for pavement evaluation. The goal is twofold: a simplified dynamic simulation of the FWD test is first presented and consequently the dynamic stiffness modulus (DSM) is proposed as an indicator of pavement subgrade performance. Computation of the DSM requires only the central deflection measured during FWD testing and can be directly performed in the field. A preliminary analysis of field data suggests that the DSM represents the average dynamic modulus of elasticity of the subgrade material. Furthermore, it follows notably well the trends in the results of conventional nondestructive testing techniques and can be consequently adopted to describe the performance of pavement subgrade soils under traffic-induced dynamic loads.

The primary purposes of joint sealing in jointed concrete pavements are to minimize moisture infiltration through the joints, to reduce moisture-related distress (such as pumping), and to prevent the intrusion of incompressible material into joints to minimize pressure-related distress (such as spalling). However, the dilemma of whether “to seal or not to seal” has frequently arisen since the benefit of improvement in pavement performance with joint sealing could not be clearly demonstrated in a number of previous studies. Premature failure of sealant has been considered as a major cause of the ineffectiveness of joint seal. Poor construction quality and material properties of sealant have been considered as problems that induce the premature failure of joint seal. In this study, other causes, which are related to the shortcomings of the AASHTO joint seal design method, which may induce premature failure of joint seal, are addressed. The first cause is in situ joint openings larger than AASHTO predictions. Variability of joint openings in a given pavement section, including erratic large openings at a considerable portion of joints, has been discussed. High chances of adhesion-type failure are plausibly related with such erratic large openings. The relationship between sealant damage and the ratio of in situ maximum joint opening to permissible sealant elongation was demonstrated in this study based on the observations from 90 joints in 16 jointed concrete long term performance pavement special pavement studies (LTPP SMP) sites. The second cause is joint freezing (defined as joints showing no movement). At frozen joints, joint seals are likely to be redundant, and a waste of money. A method for joint seal design with survival criteria is suggested in this study. In this model, joint openings are estimated based on the Lee-Stoffels model. The Lee-Stoffels model is a probabilistic model that can predict the magnitudes of joint opening with its probabilities. The joint seal designs for 16 LTPP SMP sites, based on this survival model, indicated that some sections should have sealant-type changed, to permit more elongation with the given joint reservoir, whereas other sections do not need joint seal.

A new accelerated pavement testing (APT) tool has recently been developed between relatively inexpensive laboratory testing and expensive but more realistic full-scale accelerated load testing. The one-third scale model mobile load simulator (MMLS3) applies a scaled load on a single tire smaller than a standard truck tire used in full-scale devices and can be used for both laboratory and field applications. For two hypothetical and eight actual pavement structures at a location where both full-scale APT devices and the MMLS3 were used, stress analyses were conducted to: (1) explore the hypothesis of comparable stress distribution; and (2) compare theoretical and measured rutting performance toward validating a performance prediction methodology. For the hypothetical pavement structures, the comparable stress hypothesis was upheld. Theoretically calculated rutting ratios based on stress analyses after correcting for differences in loading and environmental conditions were compared with actual measured field rutting ratios. The results were credible and demonstrated that when all influencing factors are taken into account, rutting performance under full-scale loading can be predicted based on MMLS3 results and stress analysis.

This paper describes validation results of a video image processing systems: PEEK VideoTrak 900. For this research, 12 PEEK VideoTrak 900s were installed on Interstate Highway I-75 in the Atlanta metropolitan region, and traffic movements were videotaped during several time periods. The test results showed that tracking strip type and location are critical factors in obtaining the best data accuracy. The test results showed that the system provided relatively stable speeds, but some cases showed huge volume errors. The system provided reasonable volume and speed results during the daytime, but its performance diminished during the nighttime.

This paper details a way to improve asphalt pavement durability by making specific changes to asphalt paving machines.