The Materials and Soils Section of the South Dakota Department of Highways has been cognizant of the problems connected with design of road surfaces, through the highly expansive Pierre Shales for many years. During these years they have made changes in their methods of design and construction procedures which they believed would tend to reduce the expansion of the soils and its resultant effects. They have consulted with several Materials Engineers, from different parts of the country, in an effort to find a design that would reduce if not completely eliminate the rough surface conditions that develop on roads built on highly expansive soil areas. The authors presently have under study an experimental road near the Big Bend Dam in the Missouri River Hills. The primary objectives of this experimental road are: 1. To determine if it is possible to achieve the degree of stability necessary to prevent warping of road surfacing materials by the addition of chemicals, or other additives, to the highly expansive soils; 2. To determine if additives in the in-place soils are more effective than replacing with non-expansive materials; and 3. To determine to a certain degree the economy of using stabilizing agents for the in-place soils, as compared to hauling in non-expansive soil. The authors have just completed their third year of testing on this project.
The design of safe highway alignments is a complex task, with horizontal curves being the most critical components from both safety and operational perspectives. This is because, from the tangent to curve transitions, maintaining a constant operating speed in line with driver expectations rather than the designer’s judgment is essential from a safety standpoint. The relationship between the highway elements and static/dynamic characteristics of the various vehicles on the highway geometry motivates the development of reliable safety strategies for the curve design and safety evaluation. In this study, the authors selected passenger cars (PCs) and trucks as non-compliant drivers and passenger taxis (PTs) as compliant drivers to evaluate highway safety. The authors chose 22 horizontal curves from the Ghat region of India’s Mumbai to Pune Expressway. On selected curves, 5940 samples of vehicle spot speeds using a radar gun for PCs/trucks and data from 16 PTs using an e-tracker were collected. The authors then investigated a stopping sight distance and speed-based reliability framework for assessing horizontal curve design at the curve and alignment system levels. The results show that PCs in non-compliant conditions operate faster than PTs in compliant and trucks in non-compliant conditions. Therefore, the curve has a higher probability of non-compliance, P[subscript nc], (lower reliability) for PCs in non-compliant conditions, followed by PTs in compliant and trucks in non-compliant conditions. The higher P[subscript nc] indicates more chances of crashes on the subject curves. Subsequently, the authors conducted a sensitivity analysis for the curve radius ranging from 400 to 900 m. The results show that the mid-ordinates must be changed to obtain a lower P[subscript nc] by offering a longer sight distance.
The understanding of the settlement deformation law of lakeside soft soil foundations and the definition of a reasonable settlement calculation formula are essential when setting the basis for road design and construction. The present study focuses on the application of a statistical analysis of physical and mechanical indexes to study the settlement law of the lakeside soft soil foundations, with the Jinan-Weishan expressway in China as the study case. With this aim, a correlation among the natural void ratio, compressive modulus, natural water content, density, and liquid index of the lakeside soft soil layer was performed. An improved method for settlement calculation was proposed by combining the calculation formula for predicting settlement for soft soil foundations in the lakeside area with the layer-wise summation method. Laboratory tests were performed to verify its validity. The results evidence a positive correlation of the natural void ratio with the water content and the liquid index, as well as the compressive modulus with the density. The natural void ratio reveals a negative correlation with the density, as well as the compressive modulus with the natural water content and the liquid index. Both the theoretical calculations and the experimental results illustrate that the settlement initially increases rapidly with time, then increases slowly until eventually reaching a stable state after about the 190th day. The settlement deviation between experimental findings and theoretical calculations after 190 days was less than 10%. This supports the suitability of the improved method of determining e–p curves based on density.
The primary objectives of this research are to synthesize the state-of-the-practice of existing national, state, and local agencies regulations and legislation related to autonomous and connected vehicles (AVs/CAVs), to identify infrastructure, traffic management policy, roadway design and standardization needs in order to facilitate deployment of autonomous driving, to investigate requirements for workforce development as well as changes needed for engineering curriculum for the era of autonomous driving. The results of this research will provide important implementable guidelines for the Wyoming Department of Transportation (WYDOT) decision makers to support the development of a strategic plan for cooperative automated transportation (CAT) activities in Wyoming. The recommendations in this report include: the development of Wyoming AV regulations, legislation, as well as guidance for testing and platooning procedures, the potential impacts of AVs on the physical and multimodal infrastructure, changes in traffic control devices and warrants for traffic signals.
The TR-726 research project investigates and produces the modernization of the Iowa Transportation Program Management System, TPMS. This report describes TPMS background information, application development processes, and User Manual and Developmental Specifications used to create the web-based application modernization and incorporated improvements. The three distinct sections of this report include research activities, a User Manual, and functional/technical specifications for the newly created TPMS 2020 application. TPMS 2020 is a modern multi-modular web-based software application designed to augment programming, review and acceptance, and project development requirements of Iowa’s transportation projects. The full functional process spans project concept development and programming to project turn-in for letting, with all intermediate milestone submittals and reviews documented throughout the process. The TPMS 2020 processes allow for coordinated interaction of multi-agency participants including local, regional, and state representatives. The final TPMS 2020 product will be housed and maintained by the ICEA Service Bureau, with access to all authorized users through a secure user interface, and will accommodate “real-time” secure API data exchange with the Iowa DOT PPMS software application.
The project described in this report was developed in response to a documented need for more readily available guidance related to decision-making about roadway cross section reconfigurations. More specifically, there was a need for information that might help during the decision-making process involved in converting four-lane undivided roadway cross sections to three lanes (four- to three-lane conversion) with one through lane in each direction and a two-way left-turn lane. In response to this need, this project, through consultation with practitioners, identified and developed summary responses to 14 commonly asked questions related to the planning, design, operation, and/or implementation of four- to three-lane conversions. Some of the responses to these questions may also be relevant to the process implemented for other types of conversions and roadway improvements. The summary responses to the questions identified were purposefully kept short and are contained in Appendix A of this report. All responses are also available online and are intended to be separate standalone documents. References for each summary response, if needed by the user of this guidance, are provided in Appendix B of this report. Conclusions and recommendations are summarized in this report based on the tasks completed as part of this project. The conclusions are related to the amount and relevancy of material available on four- to three-lane conversions and how the approach to roadway design and operational analysis is changing overall. Recommendations are made about the potential to answer more questions as they are identified, the development of materials specifically for elected officials, and a possible update of the Iowa guidelines for four- to three-lane conversions as an addendum to the national guidelines.
Industry guidance on the planning, operation, and design of airfield vehicle service roads (VSRs) is limited and dispersed across multiple documents. For that reason, VSR systems vary across the industry and are usually influenced by an airport’s unique operational demands, vehicle types, airfield and facility configurations, and other airport-specific characteristics. The objective of this synthesis is to describe planning, design, and operations for airfield VSR systems, including operations on apron, non-movement, and movement areas. The synthesis considers VSR issues such as maintaining the road, driver’s training, safety concerns, and operational challenges of VSR layouts. Information used in this study was attained through a literature review and interviews with 10 airport operators representing 22 airports of varying airfield sizes, activity levels, and geographic locations.
Two-stage turn queue boxes (TSTQBs) are designated for bicyclist spaces that are installed to improve the safety of left turns at intersections. This project studied the effectiveness of TSTQBs in Massachusetts by investigating left-turning bicyclist behavior at TSTQBs and correlating it with design elements. A comprehensive inventory of 88 TSTQBs was developed and a field study that allowed for capturing left-turning bicyclist behavior at six intersections in Massachusetts, including 14 TSTQB and 6 control (no TSTQB) approaches was performed. The results indicate a much lower TSTQB bicyclist utilization rate compared to other studies and no statistically significant difference in utilization at approaches that also feature bike boxes. The findings also suggest the need to install TSTQBs when crosswalk usage for bicyclists’ left-turning is high, and when approaches lack protected left-turn phasing or dedicated left-turn lanes. Future work should focus on understanding bicyclists’ and motorists’ perceptions, comprehension, and familiarity with TSTQBs as well as the impact of TSTQB dimensions and bicyclists demand to further inform design recommendations.
The United States has three million miles of rural roadways (U.S. Department of Transportation, Federal Highway Administration, 2000). Some bicyclists enjoy recreating on low-volume rural roadways because they are looking for long rides to physically challenge themselves. Some rural Americans commute to work by bicycle or travel by bike for other trips (e.g., to the grocery store), whether they are driven by environmental motivators (they do not want to further pollute the environment) or practical purposes (they have limited or no vehicles in their households but still need to make trips). Regardless of the reason, bicyclists can be found on rural roadways. While many riders may self-select onto lower-volume roadways and roadways where there are fewer large vehicles, the limited redundancy of some rural roadway networks may force bicyclists to travel on roadways with higher traffic volumes, with higher posted speed limits, and with large vehicles. With extensive miles in the rural context, the question then becomes: can providing additional pavement in the form of wide shoulders benefit both motorists, particularly those in large vehicles carrying freight, and bicyclists on roadways used by both, or should a separated facility, like a cycle highway, be considered instead? Thus, the purpose of this project is to consider whether wider road shoulders could benefit both freight and bicyclists traveling along rural roadways. Through a literature review focused on the crash experience of bicyclists, the impact of the road design on a bicyclist’s crash experience, the impact of the vehicle type and vehicle technology on a bicyclist’s crash experience, and policies impacting how and where a bicyclist may travel, recommendations and conclusions are made regarding if benefits can be had by both bicyclists and freight (a.k.a., large vehicles) within a corridor.
This report describes the results of a pop-up traffic calming project investigating exploring vehicle speed and pedestrian visibility and safety in the town center of Big Sky, Montana. This project used low-cost, temporary materials to test different strategies to assess the effects on driver and pedestrian behaviors. The community defined the goals and provided input on the project before long-construction plans were decided upon. The project included curb extensions, planters, and crosswalks designed to slow down drivers and bring more visibility to pedestrian crossings. A survey was used to collect data to determine the effectiveness of the installation.
