Institute for Transportation

About the research

Advances in technology have introduced equipment and tools to facilitate three-dimensional (3D) engineered models for construction, including the use of automated machine guidance (AMG) for grading and excavating; fine grading and base preparation; and concrete paving. Contractors traditionally use the contract plan sets to create their own 3D models, but a trend to deliver digital data as a supplement to the plan sets is emerging. Incorporating 3D model-based design has enabled project teams to communicate design intent to downstream users more effectively, and offers opportunities to improve overall efficiency of the highway infrastructure project delivery process. However, changing the medium of construction contract information also creates a procedural challenge for field inspections.

To replace two-dimensional (2D) plan sheets with 3D models could make it challenging for inspectors to accomplish field verification of contract requirements, which requires user-friendly tools specifically designed for construction inspection tasks to review contract requirements in a new, digital medium. Therefore, research is needed to aid state departments of transportation (DOTs) to evaluate the technical requirements for the selection of 3D model viewers to be implemented for model-based construction inspection.

The objective of this research is to develop a guide for state DOTs to evaluate the technical requirements for the selection of 3D model viewers for construction inspection.

About the research

The aim of this project is to develop guidelines that provide departments of transportation (DOTs) with effective practices for retrieving, depicting, and managing utility location data that may come from a host of sources; may represent existing, proposed, abandoned, or relocated facilities; may involve and identify utility conflicts; and may entail inconsistencies requiring reconciliation.

About the research

The Transportation Research Board’s (TRB’s) National Cooperative Highway Research Program (NCHRP) Synthesis 439: Use of Transportation Asset Management Principles in State Highway Agencies explores the state of practice for transportation asset management among state departments of transportation.

About the research

While it is recognized to be in the public interest to permit the installation of utility infrastructure in roadway rights-of-way, the practice has contributed to utility-related issues being one of the leading causes of delays for transportation projects. Subsurface utility engineering (SUE) is an approach state departments of transportation (DOTs) have implemented to locate utilities and assist their project-development teams with avoiding these issues.

The TRB National Cooperative Highway Research Program’s NCHRP Synthesis 583: Implementation of Subsurface Utility Engineering for Highway Design and Construction documents state DOT use and practices related to SUE and specifically examines how and when SUE is implemented during the project-design and delivery processes.

About the research

Static soil shear strength parameters in the form of friction angle and cohesion are required inputs for the safe design of foundations and earth retaining structures for virtually all transportation infrastructure including bridges, buildings, railways, wharves, piers, ports, tunnels, and pavements. Additionally, measuring the dynamic and cyclic behavior of soil in terms of stress-strain hysteresis loops as well as the associated evolution of pore water pressure is important for obtaining modulus and damping parameters for seismic design, determining post-cyclic strength, and liquefaction susceptibility analysis. These soil parameters are typically obtained by retrieving soil samples and testing them in the laboratory, which is time-consuming, expensive, and the results are sensitive to sample disturbance. Alternatively, the shear strength parameters may be estimated using empirical correlations to in situ penetration tests such as the Standard Penetration Test (SPT) or Cone Penetration Test (CPT). However, neither of these tests directly measure the shear strength of soil and instead rely upon empirical correlations that can be imprecise due to large statistical variability. Furthermore, the SPT and CPT do not subject the soil to repeated continuous cyclic loading conditions like those imposed by earthquakes or vibration sources. The goal of this project was to develop a new in situ testing device that could measure static and dynamic soil properties in the soil’s natural setting, with less sample disturbance and requiring less time than laboratory tests.

In this project, a Cyclic Borehole Shear Test (CBST) device was developed to enable the rapid in situ measurement of cyclic behavior and monotonic shear strength properties of soil. Based on the results of several field testing trials, numerous refinements and modifications were made to the system including the physical testing apparatus inserted into the borehole, the electronic and pneumatic measurement and control system, and the software control program. Comparisons of field test results to those of conventional laboratory tests demonstrated that the device can measure meaningful cyclic behavior of soil in situ. Further research will be pursued to more rigorously relate the measured displacements from the device to shear strains in the soil surrounding the borehole, and to study applications of the device to in situ measurement of the liquefaction behavior of soils. With further research, the device thus has the potential to fundamentally transform the presently empirical techniques used in practice for assessment of soil liquefaction resistance into a more mechanistic physics-based framework.

About the research

The objective of this research was to identify best practices and prepare guidelines for state departments of transportation (DOTs) on how to evaluate and charge for the accommodation of utility and communication installations on public right-of-way (ROW). The guidelines include a comparison of fees, leasing, and in-kind trading used by a majority of state DOTs. Reasons for the variance in fees, valuation methods, and other factors were analyzed to explain the variation in approaches taken by state DOTs and standardized and normalized so that the comparisons are evaluated in like terms. The guidance should provide state DOTs the means and approaches necessary to execute a fee or leasing schedule for occupancy both for general utilities and for telecommunications facilities.

About the research

The determination of the level-of-service (LOS) at signalized intersections is an important activity for decision-making in the allocation of resources for managing public roads, estimating the impact of new developments, and designing signal timing plans. The Highway Capacity Manual (HCM) methodology for signalized intersections is the most widely used method of estimating the LOS. The core of this methodology is a delay equation that takes as its inputs the demand volumes for various movements at an intersection, the signal timing, and other parameters related to the configuration of the intersection.

For right-turn movements, the current HCM methodology instructs users to obtain field measurements of the right-turn-on-red (RTOR) flow rate or else to assume that all of the right-turning vehicles execute the movement during the green interval. A consequence of this is that the estimated delay for the right-turn movement is likely overestimated. Other estimated quantities related to characteristics of the right-turn movement, such as the pedestrian delay, are also likely to be inaccurate. Furthermore, the scenario of dual right-turn lanes has not received much attention in previous studies.

The main products of this research are the models, which are documented in the report and in this summary. In addition, a practitioner guide was developed that contains documentation of the models along with a spreadsheet tool to provide sample calculations. Additionally, the RTOR volume calculations have been integrated into the HCM Computational Engine. The practitioner guide also includes a synthesis of guidance on whether to permit RTOR at a given location. In addition, during the course of this research a survey was distributed to develop an understanding of current practice with regard to RTOR. The survey results are presented in this report.

About the research

Connected and autonomous vehicle (CAV) technologies have the potential to produce a number of safety, mobility, and environmental benefits for the users and operators of the nation’s surface transportation system. Due to the rate of turnover in the existing vehicle fleet, however, infrastructure will need to be maintained for both human drivers and CAVs for some time. Additionally, uncertainty regarding CAV technology can make it difficult for agency managers to select and invest in assets supporting CAV deployment and to determine future workforce needs.

The aim of this study was to identify likely infrastructure maintenance needs due to the implementation of CAV technologies, develop guidance on measurable maintenance standards (if feasible) and the resources required to implement those standards, and assess any implications for workforce needs. Available maintenance information for key infrastructure assets identified in Phase I was collected from 39 state responses to a national survey and 18 follow-up interviews with states, municipalities, asset vendors, and maintenance contractors.

Among the most significant findings of the research was that states are acting in anticipation of CAVs, but with significant limitations in the knowledge, skills, and abilities of their workforces. Agencies addressed that gap temporarily by contracting work to third parties such as universities, vendors, consultants, and contractors. Public-private partnership (PPP) relationships also represented an effective method to pilot emerging technologies.

However, long-term adverse outcomes could result if the agency deploying the technology does not retain the knowledge gained during deployment. Because agencies were in earlier stages of implementation than expected during this project, none of the agencies or maintenance contractors interviewed had significant experience with CAV asset maintenance. As a result, maintenance standards and best practices were not sufficiently mature for documentation.

About the research

Construction Manager/General Contractor (CMGC) project delivery is an integrated team approach to the planning, design, and construction of a highway project, to control schedule and budget, and to assure quality for the project owner. The team consists of the owner, the designer, which might be an in-house engineer, and the at-risk construction manager. The aim of this project delivery method is to engage at-risk construction expertise early in the design process to enhance constructability, manage risk, and facilitate concurrent execution of design and construction without the owner giving up control over the details of design as it would in a design-build project. The objective of this research is to address the needs for CMGC guidance for evolving alternative project delivery methods. The research documents the results of a survey of state DOTs (response rate of 84 percent), a content analysis of 50 CMGC solicitation documents, and 10 case studies of CMGC projects. The research yielded a set of CMGC delivery models that are specifically adapted for DOT projects, not a regurgitation of the models in use in vertical construction. The models are described in a Guidebook for initiating and implementing a CMGC project delivery system for highway projects at transportation agencies.

About the research