The energy dissipation characteristics of steel tube clusters are investigated with a view toward using such a system as a stationary energy absorbing device. Experiments performed on small scale models made up by connecting mild steel rings cut from tube stock are described. Six different configurations were chosen for testing to establish their stability and load‐carrying capabilities, and all systems were tested both quasi‐statically and dynamically. The energy adsorption properties of all six systems are shown to be remarkably insensitive to the line of action of the loading. For a given kinetic energy, an individual system collapsed by essentially the same amount regardless of whether the impact angle was 0° or 15° with respect to the line of symmetry of the device. A design example is presented in the paper to illustrate how the results of the model tests can be applied to design a full scale impact attenuation device.

The capacity of exclusive left‐turn lanes and the passenger car equivalent of left‐turn vehicles are two parameters commonly used for the planning, design, and operation of signalized intersections. Existing methods for estimating the two parameters, however, may not have adequately accounted for the effects of signal settings and the presence of multiple opposing lanes. This study examines whether such effects are significant enough to warrant modifications of existing models. It analyzes relationships of the left‐turn movement to signal settings and the presence of one and two opposing lanes on the basis of existing understanding and computer simulation. In estimating the leftturn lane capacity, the study reveals that the use of a single formula regardless of the number of opposing lanes could lead to significant errors. It also shows that signal settings and the number of opposing lanes should be treated explicitly in estimating the passenger car equivalent.

Subgrade contact pressures under rigid pavements were analyzed using the finite element method for concrete slabs on liquid and elastic subgrades. It was found that when the maximum bending stress in the slab is made in agreement in the two analyses, the deflections and subgrade contact pressures are much greater for elastic than for liquid subgrades. Although initial bending stresses in the concrete slab are well below the concrete strengths, excessive subgrade pressures undoubtedly cause large permanent deformations in the subgrade soil, possibly increasing the stresses in the concrete slab rapidly and eventually leading to early failure of the concrete pavement. The computation of large subgrade pressures at slab edges only in pavements with weak subgrade soil supports the Corps of Engineers design practice of reduction of pavement thickness for pavements with high subgrade k values, although bending stresses in the concrete slab are only slightly affected by variations in k values. Once initial cracking in the concrete slab has occurred, the large contact pressures at slab edges computed for concrete pavements on weak subgrade must have escalated multiple cracking in the concrete slab. The subgrade contact pressures under rigid pavements should be experimentally measured to verify the results computed by the finite element method.

A technique to determine the usage of carpools on high occupancy vehicle (HOV) lanes has been developed for the Washington, D.C., region, but can be applied to any metropolitan area. Planning and testing HOV facilities is an important part in performing an alternatives analysis of future transportation systems. The approach is to adjust zone‐to‐zone average car occupancies, which are output from the traditional four‐step transportation planning process, using an observed relationship between HOV travel time savings and increased car occupancies. These “new” average car occupancies can then be used to develop discrete trip tables by vehicle occupancy sizes based on Washington, D.C., data for corridors with and without HOV facilities. These trip tables stratified by vehicle occupancy sizes can then be loaded to a highway network using a traffic assignment computer program called MULTILOAD. This program available through the Metropolitan Washington Council of Governments loads up to four trip tables to a network using capacity restraint based on the total assigned volume, and produces assigned volumes for each carpool size on every link in the network.

Recently, a great deal of importance has been placed on improving the efficiency of bus transit systems. This is motivated by a recent shift in objectives from those emphasizing expansion of transit systems to those emphasizing the conservation of transit resources. Such a reformation of objectives has focused management's attention on the bus maintenance function. In order to increase the efficiency and effectiveness of the maintenance function, managers will require accurate information systems capable of forecasting equipment failures, parts, needs, and manpower requirements. This paper describes the development of a maintenance simulation model and presents an example to demonstrate the feasibility of bus maintenance simulation modeling. The use of a bus maintenance simulation model for maintenance system planning and policy analysis is described.

Environmental concerns and physical constraints involved in the design of Interstate 70 through Glenwood Canyon, a scenic river gorge in Colorado, resulted in a design approach unique for highway projects. The Highway Act of 1976, which allowed variance from interstate standards, led to a complex and lengthy process to develop a functional and environmentally acceptable design solution. The design process is examined and several elements of the design solution are described, including terraced roadways, cantilevered roadways, retaining walls, tunnels, and a comprehensive revegetation program. The unique design process has resulted in an environmentally sensitive highway design, but the delay in implementation significantly increased the cost of the project.

Current procedures for air traffic require that certain distance separations be maintained between aircraft operations on the same runway. The capacity of the runway is inversely proportional to the time headway between operations. With a fixed distance separation this headway can be reduced by increasing the speed of aircraft. However, increased speeds will invariably result in increased runway occupancy times, and consequently, a reduction in capacity. Therefore, the attempt to match aircraft headways with runway occupancy times might prove to be a useful way of increasing capacity. The implications are that aircraft separations should be based on time headway rather than distance. Aircraft speeds and distance separations could be adjusted to achieve desired headways. The operational implications, and some technological suggestions, are presented in this paper. The safety implications of these types of procedures are identified as a subject that needs further research.

Oil field traffic is identified and an estimate of increased annual cost associated with a reduced pavement serviceability is determined. Identification of oil field traffic through photographic documentation yielded a count of the number of axle repetitions as well as a description of the physical characteristics of each vehicle. Equivalent 18 kip (8,154 kg) single axle load repetitions were determined using standard “W‐Tables” for Texas rural highways. The analytic procedure examines the effects of oil well traffic on a light‐duty pavement. Evaluation is based on the concept of pavement serviceability developed at the AASHTO Road Test. A reduced pavement service life results in an increased annual cost for a low volume light‐duty pavement section.

Although use of red turn arrows in traffic signals has been adopted by the Manual On Uniform Traffic Control Devices, a review of literature shows that there is great reluctance on the part of jurisdictions in using red turn arrow. This reluctance is rooted in the fear that the red arrow is an ambiguous and inherently unsafe traffic control device. Earlier studies of the red arrow did not present conclusive evidence of the parity or superiority of the red arrow in any traffic control setting. Based on observed violations of the red arrow and red ball at fifteen intersections of different types, located in different geographical areas, and more than 17,900 observed signal cycles, the study concludes that there is no evidence that the red arrow is less safe or more ambiguous than the red ball when used in equivalent traffic control settings. The study shows that the red arrow receives significantly less violations than the red ball, and appears to be more effective for exclusive turn control at T‐type intersections and at night time.

Moments in the intersecting pipelines can be reduced by placing flexible joints. A closed form stiffness matrix for buried pipelines with flexible joints is obtained by solving two differential equations for bending and axial effects. Numerical results demonstrate that network effects take place within a predetermined distance from the junction point, depending upon the properties of soil and interconnecting pipelines. The pipe joint effect occurs within π/2 pipe diam of the joint. Analytical expressions have been provided for the distribution of the axial pipe forces based on the resistance of the soil.

The problem of subgrade rutting is an important factor in the overall structural design system of flexible pavements. This paper introduces the parameter stress factor in pavement design and research as an expedient and useful test to check the subgrade rutting potential in a flexible pavement. The larger the computed stress factor in the subgrade is, the greater the potential of the pavement to rut. If several different types of pavements are designed for a given subgrade soil and for a given aircraft load at the same performance level, the pavement with the largest stress factor will most probably have the greatest potential of subgrade rutting. Also for a given subgrade soil, if two pavements are designed for two different aircraft loads at the same performance level, the heavier aircraft load will have a greater stress factor in the subgrade.

The problems associated with traffic signal maintenance have intensified in recent years as more sophisticated equipment has been installed, and the lack of maintenance has resulted in systems operating in an unacceptable manner. Recognizing this situation, a project was undertaken to establish general guidelines for maintenance of traffic signals, including control equipment, signal poles, and other relative hardware. Information was gathered from a number of sources, including a literature search, the use of questionnaires for both maintenance contractors and municipal agencies, and field trips to municipal maintenance departments. A classification for maintenance was developed, which was divided into preventive, response, and design modification. Guidelines were developed to evaluate a municipality's capabilities to perform traffic signal maintenance and to determine present‐day manpower and equipment requirements. Using these procedures, a municipality can also estimate their future maintenance cost.