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FY 2018 TRC Projects




Evaluation of WIM Auto-Calibration Practices and Parameters   Performance-Based Asphalt Mixture Design (PBD) for Arkansas

Weigh-in-Motion (WIM) systems capture weight and axle configurations of vehicles using the state highway network. This data serves as valuable and essential input for evaluating the performance of our transportation infrastructure.  In particular, WIM data is needed to support Federal truck size and weight regulations, and to design, maintain, and preserve pavements.  To produce accurate weights, sensors must be calibrated at installation and at regular intervals following the procedures outlined in ASTM E1318.  Poor scale calibration can lead to significant errors in determining the load on the pavement: a 10% over-estimation in axle weight results in 45% overestimation of equivalent single axle loads (ESALs).  On-site calibration requires repeated passes over the sensors of test vehicles with known weights. This is a time consuming and expensive process.  Therefore, several states have adopted auto-calibration procedures developed by WIM vendors.  Auto-calibration is an algorithmic procedure by which weights measured by the WIM sensor are adjusted based on tunable parameters set by the WIM vendor. The parameters should reflect site conditions such as truck conditions (e.g. average weight of steering axles) and environmental conditions (e.g. temperature and aging).  For auto-calibration techniques to be effective, a state must monitor and understand site conditions used to set parameters.  The proposed research will evaluate the auto-calibration techniques used for the AHTD’s 40+ piezoelectric sensors.  This will ensure that truck size and weight measurements gathered from WIM accurately reflect the loads and configurations of trucks traversing Arkansas highways.

Historically asphalt mixture design has been based on component specifications and volumetric properties. With volumetric based design, engineering properties of asphalt mixtures are controlled only indirectly -- influenced by properties of the components and proportions of each component.  Superpave was intended to include performance-based tests -- that is, tests that measure engineering properties directly related to performance, but these tests proved to be non-implementable.  As a result, Superpave is based solely on volumetric properties.  Performance-Based Mixture Design (PBD) includes performance tests to evaluate rutting potential, cracking potential and moisture resistance during the mixture design process.  Performance tests provide a more direct evaluation of expected performance than volumetric properties.  Such tests can better characterize the effect of new materials and processes (e.g. RAP, RAS, Warm-Mix) as well as changes to mix design criteria.

Recent surveys (NCHRP Synthesis 492; FHWA Expert Task Group; LTRC; Arkansas Asphalt Pavement Association) have indicated concern that current mixture design procedures do not ensure adequate field performance.  Of prime concern is early-age cracking in asphalt pavements.  In addition, the AAPA survey suggests differences in the cracking performance of mixtures with different aggregates (e.g. sandstone versus limestone) in Arkansas.  TRC 1404 identified mixture design related issues as a significant contributor to early-age pavement distress.  A key item to note is that many agencies have implemented a 'rutting test' to accompany the Superpave volumetric design process (AASHTO M323, R35) -- however, only a few have implemented a cracking test into routine mix design (although surveys indicate the number is growing).

Research is needed to develop/adapt and implement a 'cracking test' for asphalt mixture design - and to use this test in conjunction with the current APA rutting test (AHTD Test Method 480) to shift mixture design in Arkansas to a performance basis, rather than a volumetric basis.  In addition, the research should re-evaluate the effectiveness of the current method for estimating resistance to moisture damage (AHTD Test Method 455A) - and develop/adapt alternate methods as appropriate. A performance-based mixture design system will provide a much higher degree of confidence that Arkansas roadways will not experience materials-related premature distresses and failures.






Mapping Subsurface Conditions for Transportation Applications

  Annual Average Daily Traffic (AADT) Estimation for Local Roads

Each year AHTD spends millions of dollars to deal with troublesome soil and rock layers, which cause slope stability issues along roadways or require removal of rock layers. The remediation of slopes or removal of bedrock can be both time consuming and expensive. While slope stability and shallow bedrock issues may be unavoidable or even expected on certain projects, unexpected subsurface conditions during construction can lead to significant cost overruns, change orders, and construction delays. If a more accurate/complete 3D understanding of the subsurface conditions was available during the design phase, some problems could be avoided or at least budgeted for during construction. Currently subsurface conditions are assessed on transportation projects using drilling and sampling along the project alignment. While this provides an acceptable level of accuracy for projects where problematic soil and rock layers depth and thickness are consistent, significant errors can exist when conditions are variable both inline and crossline to the alignment. To provide a more complete picture of the subsurface layering where conditions are quite variable, a continuous 3D subsurface profile can be developed rapidly using Capacitively Coupled Resistivity (CCR). CCR is a drag along array resistivity system that measures the electrical resistance of soil and rock formations. This system can be used to provide continuous 3D models of the subsurface and has been shown to be effective at identifying weak clay seams, which exhibit higher moisture levels (due to high PI) and bedrock location (due to lack of moisture). Knowledge regarding the location of these layers can be used in slope stability analysis and used for developing better estimates of rock cut quantities on transportation projects.


Moving Ahead for Progress in the 21st Century (MAP‐21) requires AHTD to report Average Annual Daily Traffic (AADT) for every paved roadway across the state, whether it is owned by the state, county or city.  Traffic counts are expensive and the requirement of AADT for each intersection and intersecting roadway is a monumental task, both logistically and financially.  Additionally, there are no viable means to accomplish this under the current staffing or funding scenarios.




Access Management Implementation    

Access management concepts were well in place by the 1970s, and state departments of transportation begin to implement access management programs in the 1980s. Since then, research and experience has contributed to the evolution of the concepts and the implementation mechanisms. Even though access management improves both traffic flow and safety, the extent to which state and local agencies have adopted it varies widely. Adoption and implementation of access management is challenging because it cuts across organizational lines and involves a number of interrelated practices. Before an agency embarks upon an access management program, it should examine current organizational structure and practices within the agency, and then develop a plan that presents a detailed strategy for adoption and implementation.