This paper describes laboratory and field tests conducted using a new fiber stabilization technique for sands. Laboratory unconfined compression tests using 51 mm long monofilament polypropylene fibers to stabilize a poorly graded (SP) sand showed an optimum fiber content of 1% (by dry weight). Field test sections were constructed and traffic tested using simulated C-130 aircraft traffic with a 13,608 kg tire load at 690 kPa tire pressure and a 4,536 kg military cargo truck loaded to a gross weight of 18,870 kg. Test results showed that sand-fiber stabilization over a sand subgrade supported over 1,000 passes of a C-130 tire load with less than 51 mm of rutting. The top 102 mm of the sand-fiber layer was lightly stabilized with tree resin to provide a wearing surface. Based on limited truck traffic tests, 203 mm thick sand-fiber layer, surfaced with a spray application of tree resin, would support substantial amounts of military truck traffic.

Quarter-car model-based indirect statistics of road surface roughness are analyzed in this paper. The stochastic process theory is used to establish the relationship between the international roughness index (IRI) statistic of a quarter-car response and the power spectral density (PSD) of road random excitation. Under the circumstance of a linear vehicle model and homogeneous roughness with a zero-mean Gaussian distribution, we prove that the average of the absolute response of the quarter-car model is directly proportional to the standard deviation of that response quantity. This result enables us to further correlate the indirect statistics with PSD roughness. A theoretical relation between the IRI and the PSD roughness is established. Based on the road classification proposed by the International Standards Organization (ISO), it is found that a linear correlation exists between the IRI and the standard deviation of roughness. Furthermore, corresponding to the ISO PSD-based road classification, an IRI-based road classification is provided to categorize pavement into five classes, ranging from very good surface condition to very poor surface condition.

The design method for pavements in the Takalimakan desert was proposed through the investigation of test roads and theoretical analysis. The function of geotextile in pavement structures is analyzed by the shear lag model, with a result that the shear bearing capacity of geotextile is proportional to its tensile modulus and the second derivative of its tensile deformation. Combining the layer-peeling method, a bearing plate method, and modulus back—calculation, the modulus of resilience of each layer in the pavement structure is determined. By means of multilayer elastic theory, the influence of contact conditions in the pavement on the tensile stresses and displacement is quantitatively analyzed. Stresses for unbonded wearing course and gravel-base course increase by more than four times. Change of contact conditions has little effect on the surface deflection. Therefore, the variation of surface deflection cannot reflect the shear instability between subbase and subgrade. Direct shear testing must be utilized to guarantee the shear stability in the pavement structure.

Satisfactory maintenance of its highway network is essential for any nation's economic growth. A pavement management system (PMS) formulated according to specific needs and resources of a particular highway maintenance agency would assure satisfactory pavement performance with minimal maintenance cost. Since the collection of detailed pavement condition data is extremely costly and time-consuming, innovative approaches for rapid data collection is in increasing demand among highway agencies with limited PMS budgets. A time-saving and effective data collection approach based on subjective judgment is introduced by the writers for rating predominant distress types found in asphaltic pavements. Inclusion of both severity and extent ratings of distresses is expected to provide a strong basis for eventual maintenance cost computations. The mathematical techniques of fuzzy sets are used to deal with the subjectivity associated with human judgment of distress severity and extent. In addition, the relative importance of each distress type with respect to maintenance is also utilized in the determination of the combined condition index. Several fuzzy aggregation and ranking approaches are explored and the one with the highest computational efficiency is employed for ranking pavement sections with respect to rehabilitation needs. Finally, a fuzzy pavement condition forecasting model is also developed by incorporating subjective probability assessments regarding pavement condition deterioration rates, in the Markov transition process. Specific transition probability matrices for different distress types are used in this approach to overcome the deficiencies of the traditional PCI approach. The potential applicability of the methodology is tested on the major pavement network of Sri Lanka and its effectiveness and the execution ease are demonstrated.

Highway pavement maintenance is very expensive not only in terms of costs to the responsible agencies but also in terms of disruptive delays to users. Construction and maintenance activities on four-lane highways (with two lanes in each direction) often require the closure of one of the two travel lanes. Longer work zones tend to increase the user delay costs. Maintenance work can be performed more efficiently, i.e., with fewer repeated setups, in longer zones. A relatively simple mathematical model is developed to optimize work zone lengths on four-lane highways where one lane in one direction at a time is closed. The objective is to minimize the total cost, including the agency cost, the accident cost, and the user delay cost. The optimized variable (e.g., work zone length) and the sensitivity results generated from a numerical example are presented in this study. With user-specified input parameters, this model can be used to optimize work zones on four-lane highways for a wide variety of circumstances.

This paper compares the capacities of shared left turn lanes obtained by four methods for varying lane configurations, through and left turn volumes, and traffic signal timings. The 1997 Highway Capacity Manual (HCM), Canadian, SIDRA, and Levinson methods were analyzed for left turn volumes ranging up to 250 vehicles per lane per hour (vph) for both 60- and 90-s cycles, assuming 50% effective green time per cycle. Scenarios were tested assuming both equal and unequal volume. More than 700 individual computations were performed. The methods provide generally consistent patterns for each scenario tested. The 1997 HCM method (unlike the 1994 HCM method) consistently provided higher capacities than the other three methods for single-lane approaches. The SIDRA method consistently provided the lowest capacities on multilane approaches where left turn volumes exceed 100–150 vph. The research suggests further field tests and analyses to see if modifications in left turn equivalency factors for single-approach lanes associated with the 1997 HCM method are desirable to bring the results more in line with those of the other models. The general consistency of the shared lane capacities obtained by the Canadian and Levinson methods, along with their simplicity, clarity, and ease of use make them well suited, especially for quick response applications.

This paper compares the performance of roundabouts with four leg intersections under yield control, two- and four-way stop control, and signal control for various traffic conditions using the SIDRA package. Such conditions include variations in volume levels, turning volume splits, number of approach lanes, and lane widths. The results from the analysis indicate that roundabouts are the best alternative designs for intersections with two-lane approaches that carry heavy through and/or left traffic turning volumes. The performance of roundabouts compares well to the performance of signalized intersections with one-lane approaches and heavy traffic volumes. Roundabout capacities are found higher than capacities of signal controlled intersections with two- and three-lane approaches for any proportion of left-turning traffic volume. This study provides recommendations to traffic engineers on the conditions under which roundabouts perform better than controlled intersections and, thus, should be considered as design alternatives.

This paper describes the development of accident prediction models for estimating the safety performance of urban arterial roadways in the Greater Vancouver Regional District, British Columbia, Canada. The traffic- and road-related variables that appear to underlie the occurrence of accidents are examined and models that explain the occurrence of accidents as a function of these variables are developed. To determine which variables have a significant effect on the safety of urban arterials, the study investigated a large number of models with different combinations of these variables. The investigation led to the conclusion that, among those variables examined, the ones that had a significant effect on accident occurrence were section length, traffic volume, unsignalized intersection density, driveway density, pedestrian crosswalk density, number of traffic lanes, type of median, and type of land use. The models were used to investigate the effect of the median type on accident occurrence. The study estimated that conversion from an undivided arterial to one with a raised-curb median could result, on average, in a 10% accident reduction.

This paper describes a study to investigate hazards with the potential to close the Desert Road section of New Zealand's major north-south road link, State Highway 1. The risks caused by snow and ice, volcanic eruptions and lahars, earthquakes, and traffic accidents were evaluated in terms of their expected frequency of occurrence and duration of road closure. The effects of road closures on traffic flow patterns were assessed using a traffic assignment model, with and without allowing for the elasticity of travel demand. A probability distribution for the annual economic impact of road closure was found for each hazard. The viability of various mitigation options for reducing the risk of road closure was assessed, using probability distributions of the benefit-cost ratio for the mitigation options.

The effects of the October 1994 gasoline price increase in Nigeria on urban travel expenditures are examined. Results show that, although the established inverse relationship between travel money expenditure and income has not changed, significant changes have occurred in travel money expenditures across socioeconomic strata. The fuel price elasticities of travel expenditures were below unity overall and across all socioeconomic strata, except for the highest age group considered. Thus the energy policy change has, in general, not produced adverse effects on travel expenditure. Elasticities are apportioned not only by income level but also by the levels of other socioeconomic factors that are usually considered in travel demand studies. Age has proved particularly relevant because elastic responsiveness was recorded for the respondents in the oldest age bracket. One implication of this is that in the future it may be necessary to evolve energy and transportation policies that will ensure preferential treatment for the elderly to cushion the effect of energy policy changes on this group of people.

A high accident trend of rental cars is observed. The size of the problem attracted the attention of researchers, officials, and legislators. The goal of this study is to evaluate the problem and to identify possible causes. A questionnaire survey was conducted to identify potential causes. Statistical analysis (ANOVA) was used to decide significant causes. Study analyses include comparison of accident rates before and after implementation of modifications to regulations controlling rental cars. Analyses indicate that the problem is correlated to behavioral trends. The study reveals that the high accident rate of rental cars is mainly attributed to a low level of understanding and adherence to traffic regulations. The low level of adherence is mainly associated with inadequate driving experience and the young age of rental-car drivers. Findings of this study are applicable in many other countries, especially in ones with drivers of similar behavioral characteristics.