In this paper, a series of unconfined compressive strength (UCS) tests were performed to study the effect of cement content, zeolite content, initial moisture content, number of freeze-thaw cycles, and curing time on the UCS of low-plasticity silty sand-clayey sand. The results indicate that zeolite can be used along with cement as a stabilizer to enhance mechanical behavior of the soils. The specimens containing cement and zeolite show better response with a higher UCS than the stabilized samples with cement or zeolite alone. The addition of zeolite has an important effect on the increase in both UCS value and failure strain of cement-stabilized specimen. However, the stress-strain curve of stabilized specimens is not influenced significantly by the increase of zeolite content from 3 to 9%. The UCS values of the stabilized specimens decreased as the number of freeze-thaw cycles increased. The cement-stabilized samples have freeze-thaw durability when zeolite content increases from 3 to 9%. The stabilized specimens with 6% cement and 9% zeolite have slightly higher freeze-thaw durability than other specimens. The UCS of the specimens compacted on the dry side is more than that of the compacted sample on the OMC or wet side of optimum for given additives contents. The specimens compacted on the dry side of optimum exhibited a lower failure strain. The implication of this work is significant in geotechnical practice; it provides a general knowledge of stabilization of soils using cement and zeolite and the quantities to use to achieve the desired geotechnical properties.

Transportation networks respond differently to applied policies. The Tehran Metropolitan Area has one of the most complex networks with complex users, which has experienced many of these policies change within the past decades. In this study, some of these policies and their effect on air pollution is investigated. The goal is to pinpoint the variables which have the most effect on various transportation models and investigate how new policies should be focused. In order to do so, long-term variations of air pollution monitoring stations were analyzed. Results show that the most significant parameter that may affect air pollution is users' behavior due to the lack of a public transportation network and its level of comfort. The results of this study will be useful in developing new policies and evaluating their long-term consequences in appropriate models.

Transport forms one of the primary needs in all categories of the population in modern society; it is of paramount concern for traffic engineers, transport planners, and policy makers to understand and evaluate the quality of service being provided by the transport facilities designed by them. This paper presents an investigation in profile geometric design and traffic flow operation on two-lane two-way highways and provides analyses that will help in a better understanding of traffic operation on these facilities to select the optimum profile configuration. The effects of influencing parameters consisting of grade, length of grade, traffic composition, and traffic volume are evaluated and finally a systematic procedure to evaluate flow rate under the base condition is presented. Finally, based on these achievements an algorithm is introduced to select optimum Finished Ground of profile view. Results show that the percentage of heavy vehicles has a contributing effect on traffic operation so that the optimum profile configuration is incredibly affected by this factor. Source data have been obtained from Highway Capacity Manual (HCM) as a pioneer document in respect of quantifying the concept of capacity for a transport facility.

Poor urban air quality is one of the most pressing environmental problems, and the rapid growth in the number of motor vehicles is a major contributor to it. To tackle this problem, low emission zones (LEZs) were introduced and they have been applied in many of the mega cities around the world. Yet, a scientific approach to design the boundaries of LEZs is missing. This study develops an innovative model to address this gap, using total vehicle kilometers traveled (VKT) as the basis. The model allows defining and/or optimizing the LEZ boundaries. It is applied for the Tehran metropolitan area, as a case study, and the results show the optimality of the existing LEZ boundaries; however, they challenge the efficiency of the proposed policies on modifying current boundaries.