Research Digest FORWARD ALL REQUESTS TO: The University of Texas at Austin Center for Transportation Research LIBRARY 1616 Guadalupe St. | Suite 4.202 | Austin, Texas 78701 Phones: (512) 232-3126 and (512) 232-3138 Email: ctrlib@austin.utexas.edu In this Issue:
State DOT Research Reports -- VIRGINIA
Table of Contents Item 1.
Feasibility of Using Jobs / Housing Balance in Virginia Statewide Planning : Final Report (VTRC 10-R26).........................................................................................................................................................
1
Item 2.
Evaluation of the Lightweight Deflectometer for In-Situ Determination of Pavement Layer Moduli : Final Report (VTRC 10-R6)................................................................................................................
1
Item 3.
Safety Performance Functions for Intersections on Highways Maintained by the Virginia Department of Transportation (VTRC 11-CR1)...............................................................................................
2
Item 4.
Quantifying the Benefits of Coordinated Actuated Traffic Signal Systems : A Case Study (VTRC 11-CR2)........................................................................................................................................................
2
Item 5.
Evaluation of Environmental Impacts of Two Common Restoration Methodologies for Pipes that Convey Stormwater Runoff (VTRC 11-CR3)................................................................................................ 3
Item 6.
Development of a Framework for Evaluating Yellow Timing at Signalized Intersections (VTRC 11-R12)...................................................................................................................................................................
3
Item 7.
An Evaluation of the Potential Use of Non-Nuclear Density Gauges for Asphalt Concrete Acceptance (VTRC 11-R15)................................................................................................................................
4
Item 8.
Field Trials of High-Modulus High Binder-Content Base Layer Hot-Mix Asphalt Mixture : Final Report (VTRC 11-R2)..................................................................................................................................
5
Item 9.
Analysis of the Mechanistic-Empirical Pavement Design Guide Performance Predictions : influence of asphalt material input properties (Final Report) (VTRC 11-R3)................................................
5
Item 10.
A Planning-Level Methodology for Identifying High-Crash Sections of Virginia's Primary System : Final Report (VTRC 11-R4)................................................................................................................
6
Item 11.
Investigation of Optimized Mixture Design for Superpave Surface Mixtures (VTRC 11-R5)..................
6
Item 12.
Characterization of Unbound Pavement Materials From Virginia Sources for Use in the New Mechanistic-Empirical Pavement Design Procedure (VTRC 11-R6)..........................................................
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Item 13.
Examination of an Implemented Asphalt Permeability Specification (VTRC 11-R7)................................
7
Item 14.
Best Practices in Traffic Operations and Safety, Phase II : Zig-zag Pavement Markings (VTRC 11-R9)........................................................................................................................................................................
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Research and Technology Implementation Office
June 2011
Research Digest Item 1 Feasibility of Using Jobs / Housing Balance in Virginia Statewide Planning : Final Report VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 10-R26 • 2010 The Code of Virginia (§ 33.1-23.03) requires that the Statewide Transportation Plan include "quantifiable measures and achievable goals relating to... job-to-housing ratios." Such ratios reflect jobs/housing balance, defined as an equivalence in the numbers of an area's jobs and area residents seeking those jobs. This report identifies planning policies based on jobs/housing balance, examines the impact of such balance on commuting, and demonstrates how to measure this balance using Virginia data. Full-text of this report ia available for free download from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r1.pdf
Item 2 Evaluation of the Lightweight Deflectometer for In-Situ Determination of Pavement Layer Moduli : Final Report VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 10-R6 • 2010 The quality of base and subgrade construction has conventionally been evaluated using specifications based on density and moisture content. Such specifications for highway base and subgrade require the use of a nuclear density and/or moisture gauge that poses potential health hazards to the operator and requires expensive certification and monitoring. Moreover, density and moisture do not relate to pavement design input parameters or performance. The fundamental material properties such as elastic and resilient moduli that are key inputs in the new mechanistic empirical-based design cannot be obtained from density and moisture content measurements. The primary objective of this study was to investigate the suitability of the lightweight deflectometer (LWD) to measure in-situ pavement layer moduli. The LWD, along with two pother devices, the GeoGauge and dynamic cone penetrometer (DCP), were used to measure and monitor subgrade and base layer moduli during construction. Three existing gravel roads were also tested. Full-text of this report ia available for free download from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/10-r6.pdf
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Research and Technology Implementation Office
June 2011
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Research Digest Item 3 Safety Performance Functions for Intersections on Highways Maintained by the Virginia Department of Transportation UNIVERSITY OF VIRGINIA. DEPT OF CIVIL & ENVIRONMENTAL ENGINEERING
VTRC 11-CR1 • 2010 The Federal Highway Administration (FHWA) has developed a procedure for identifying highway locations that have the highest potential for crash reduction (ITT Corporation, 2008). A critical component of this method is the use of safety performance functions (SPFs) to determine the potential for crash reductions at a location... Although the Safety Analyst User’s Manual presents several SPFs for intersections, these were developed using data from Minnesota. FHWA also suggested that if feasible, each state should develop its own SPFs based on crash and traffic volume data from the state, as the SPFs that are based on Minnesota data may not adequately represent the crash characteristics in all states. SPFs for intersections in Virginia were developed using the annual average daily traffic as the most significant causal factor, emulating the SPFs currently suggested by SafetyAnalyst. The SPFs were developed for both total crashes and combined fatal plus injury crashes through generalized linear modeling using a negative binomial distribution. Models were also developed for urban and rural intersections separately, and in order to account for the different topographies in Virginia, SPFs were also developed for three regions: Northern, Western, and Eastern. This report covers Phases I and II of the study, which includes urban and rural intersections maintained by VDOT. Statistical comparisons of the models based on Minnesota data with those based on the Virginia data showed that the specific models developed for Virginia fit the Virginia crash data better. The report recommends that VDOT’s Traffic Engineering Division use the SPFs developed for Virginia and the specific regional SPFs suggested in this report to prioritize the locations in need of safety improvement. Full-text of this report ia available for free download (1.2 MB) from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-cr1.pdf
Item 4 Quantifying the Benefits of Coordinated Actuated Traffic Signal Systems : A Case Study VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 11-CR2 • 2010 Coordinated actuated traffic signal systems have been widely implemented for the past few decades because they provide better progression along the major corridors through proper coordination. However, little has been done to quantify the benefits that can be obtained from coordinated traffic signal systems. Most efforts reported in the literature focused on system performance estimated from simulation software as opposed to field studies. The purpose of this study was to quantify the benefits of coordinated actuated traffic signal systems by conducting an analysis of before-and-after data. The travel time on the coordinated arterials and the stopped delay on a few key approaches were selected as measures of effectiveness. Synchro, a macroscopic traffic signal timing evaluation and optimization software, was used to generate the coordinated actuated traffic signal timing plans for comparison purposes. In addition, the performance of an adaptive split feature, implemented within the coordinated actuated traffic signal system, was evaluated through a before-and-after study. Full-text of this report ia available for free download from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-cr2.pdf _______________________________________________________________________________________________
Research and Technology Implementation Office
June 2011
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Research Digest Item 5 Evaluation of Environmental Impacts of Two Common Restoration Methodologies for Pipes that Convey Stormwater Runoff VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 11-CR3 • 2010 The Virginia Department of Transportation (VDOT) is responsible for the maintenance of underground pipes that convey stormwater runoff from roadways and other relatively impervious surfaces. Due to normal fatigue, cracks can develop in these pipes over time. Excavation and replacement of the damaged pipe section are expensive, intrusive, and time-consuming. As an alternative, VDOT has used pipe-repair technologies that involve the insertion of the synthetic liner material inside the damaged pipe. Although this technology can effectively seal water leaks caused by cracks in the pipe, the environmental impact of chemicals that leach from the liner materials into water in the pipe are not known. In this work, we have investigated two common commercial pipe-repair technologies: Ultraliner and Troliner. Both technologies employ a synthetic liner material. Troliner installation also requires the use of grout that helps to provide an effective seal between the synthetic liner and the original host pipe wall. Full-text of this report ia available for free download (3.0 MB) from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-cr3.pdf
Item 6 Development of a Framework for Evaluating Yellow Timing at Signalized Intersections VIRGINIA CENTER FOR TRANSPORTATION INNOVATION AND RESEARCH (VCTIR)
VTRC 11-R12 • 2011 Studies show that the proper design of clearance intervals has significant implications for intersection safety. For example, in 2001, approximately 218,000 red-light-running crashes occurred at signalized intersections in the United States. These crashes resulted in nearly 181,000 injuries and 880 fatalities and an economic loss of $14 billion. Driver behavior while the driver is approaching high-speed signalized intersections at the onset of a yellow indication varies as a function of many parameters. Some of these parameters are related to the driver’s attributes, e.g., age, gender, perception-reaction time, and acceptable deceleration levels. Other parameters that relate to the intersection geometry include the approach speed, distance, and time to the intersection at the onset of the yellow indication. This study developed a novice approach for computing the clearance interval duration that explicitly accounts for the reliability of the design (probability that drivers are not caught in a dilemma zone). Lookup tables based on the limited data available from this study are provided to illustrate how the framework could be used in the design of yellow timings. The approach was developed using data gathered along Virginia’s Smart Road test facility for dry and clear weather conditions for two approach speeds: 72.4 km/h (45 mph) and 88.5 km/h (55 mph). Each data set includes a complete tracking of the vehicle every deci-second within 150 m (500 ft) before and after the intersection. A total of 3,454 stop-run records were gathered. These include 1,727 records (687 running records and 1,040 stopping records) for an approach speed of 45 mph and 1,727 records (625 running records and 1,102 stopping records) for an approach speed of 55 mph. Using these data, models that characterize driver perception-reaction times and deceleration levels were developed. The application of the proposed approach demonstrates that the current design procedures are consistent with a reliability level of 98%. Full-text of this report ia available for free download (2.4 MB) from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r12.pdf _______________________________________________________________________________________________
Research and Technology Implementation Office
June 2011
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Research Digest Item 7 An Evaluation of the Potential Use of Non-Nuclear Density Gauges for Asphalt Concrete Acceptance VIRGINIA CENTER FOR TRANSPORTATION INNOVATION AND RESEARCH (VCTIR)
VTRC 11-R15 • 2011 This report describes the results of a study using non-nuclear density gauges (NNDGs) to measure the in-situ density of asphalt concrete (AC) material in Virginia. The study compared the NNDG results with those obtained from the use of two traditional AC density acceptance methods: the core method (AASHTO T 166) and the nuclear density gauge (NDG) method. Although these two methods are the most widely used methods of accepting AC density, the core method is time-consuming and destructive and involves bulky test setups and the NDG method, although portable and non-destructive, is associated with safety concerns related to the presence of radioactive materials in the gauge. The purpose of the study was to evaluate the use of two NNDGs as a potentially safe, portable, and expedient method of measuring AC density—a key indicator of pavement performance. The direct comparison of NNDG and core density and the acceptance rates with the use of NNDGs and NDGs were the focus of the study. Extensive field and laboratory tests were conducted to determine AC density using two models of NNDGs (i.e., the Troxler PaveTracker Plus and the TransTech Model PQI 301) and one model of an NDG (i.e., the Troxler Model 4640-B). Density measurements of AC cores/plugs taken at gauge testing locations were conducted in the laboratory in accordance with AASHTO T 166 for comparisons. The results of the field testing showed that NNDG measurements were not well correlated with core density or NDG measurements. However, there was good agreement between readings from NNDGs and NDGs in terms of identifying core cutting locations (67%), control strip acceptance (75%), and test section acceptance (95%). This apparent contradiction between the acceptance rate among the gauges and the poor correlation could be explained by the relatively low ranges in measured field density (0-5 lb/ft3), which is within the precision ranges of the gauges used. Full-text of this report ia available for free download (303 KB) from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r15.pdf
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Research and Technology Implementation Office
June 2011
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Research Digest Item 8 Field Trials of High-Modulus High Binder-Content Base Layer Hot-Mix Asphalt Mixture : Final Report VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 11-R2 • 2010 The purpose of this study was to document the field experience of the Virginia Department of Transportation (VDOT) in the use of high-modulus high-binder-content (HMHB) base layer hot-mix asphalt (HMA) mixtures. Information was gathered with regard to the construction of HMHB base mixtures at three field trial sites in Virginia, and laboratory tests were conducted on samples that were gathered before and during construction. The three locations were the sites of deep rehabilitation or new construction, and HMA base mixtures were used at designed asphalt content, designed asphalt content plus 0.4% additional asphalt, and/or designed asphalt content plus 0.8% additional asphalt. This study documented the field and laboratory knowledge gained by VDOT when producing and placing HMHB mixture test sections in an effort to achieve a long-lasting perpetual-type flexible pavement. These designs offer the potential to reduce fatigue cracking by incorporating additional asphalt binder and reducing the void content of the mixture. The use of an adjusted binder grade or RAP to maintain the necessary stiffness for high binder contents should provide the necessary stiffness to minimize the susceptibility for rutting during service. Quantification of the economic benefits of using HMHB mixtures is a future goal that can be realized after longer term study of field performance. Full-text of this report ia available for free download from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r2.pdf
Item 9 Analysis of the Mechanistic-Empirical Pavement Design Guide Performance Predictions : influence of asphalt material input properties (Final Report) VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 11-R3 • 2010 The Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures (MEPDG) is an improved methodology for pavement design and the evaluation of paving materials. The Virginia Department of Transportation (VDOT) is expecting to transition to using the MEPDG methodology in the near future. The purpose of this research was to support this implementation effort. A catalog of mixture properties from 11 asphalt mixtures (3 surface mixtures, 4 intermediate mixtures, and 4 base mixtures) was compiled along with the associated asphalt binder properties to provide input values. The predicted fatigue and rutting distresses were used to evaluate the sensitivity of the MEPDG software to differences in the mixture properties and to assess the future needs for implementation of the MEPDG. Two pavement sections were modeled: one on a primary roadway and one on an interstate roadway. The MEPDG was used with the default calibration factors. Pavement distress data were compiled for the interstate and primary route corresponding to the modeled sections and were compared to the MEPDG-predicted distresses. The implementation of these recommendations and use of the MEPDG are expected to provide VDOT with a more efficient and effective means for pavement design and analysis. The use of optimal pavement designs will provide economic benefits in terms of initial construction and lifetime maintenance costs. Full-text of this report ia available for free download from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r3.pdf _______________________________________________________________________________________________
Research and Technology Implementation Office
June 2011
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Research Digest Item 10 A Planning-Level Methodology for Identifying High-Crash Sections of Virginia's Primary System : Final Report VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 11-R4 • 2010 The Virginia Department of Transportation (VDOT) has been developing safety performance functions (SPFs) as a way to identify sites with a potential for safety improvement more effectively. An SPF estimates the expected safety performance of a roadway as a function of its characteristics. Using SPFs, VDOT can identify which roads have a significantly higher number of crashes than would be expected based on site conditions. Other VDOT studies have developed SPFs with a microscopic perspective that separately examine individual intersections or discrete roadway segments. The purpose of this study was to develop an SPF-based methodology to conduct more intermediate-scale safety analyses. VDOT's Traffic Engineering Division indicated that such a methodology would be useful for corridor screening and planning-level applications. The scope of the study was limited to the following roadway types in Virginia's primary system: rural two-lane, rural multi-lane divided, rural multi-lane undivided, urban two-lane, urban multi-lane divided, and urban multi-lane undivided. For each type, roadway inventory data, traffic volume data, and crash data from 2003 through 2007 were compiled and integrated into a database. The study then took an approach that diverged from that of other SPF research to develop intermediate-scale SPFs. Full-text of this report ia available for free download from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r4.pdf
Item 11 Investigation of Optimized Mixture Design for Superpave Surface Mixtures VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 11-R5 • 2010 Since the adoption of the Superpave asphalt mixture design, it has been suspected that mixtures have been deficient in asphalt content, even though some changes have been made in the design specifications. The primary purpose of this study was to determine if Virginia’s current Superpave mixtures are deficient in asphalt and if they are to determine ways to remedy the situation. Analysis of current 9.5 mm mixture production data and production data of similar mixtures produced prior to the adoption of Superpave revealed no significant difference in asphalt content. Gradation differences may have affected these results. Additional analysis of the production 12.5 mm mixtures possibly over certain time intervals is recommended. Analysis of several mixtures in the laboratory revealed that some mixtures may be able to tolerate more asphalt, thereby improving durability; however, additional asphalt would be detrimental to the performance of other mixtures. Based on the findings of this study, the Virginia Department of Transportation’s specifications regarding mixture design should not be changed at this time, but additional research work is justified. Full-text of this report ia available for free download (152 KB) from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r5.pdf
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Research and Technology Implementation Office
June 2011
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Research Digest Item 12 Characterization of Unbound Pavement Materials From Virginia Sources for Use in the New MechanisticEmpirical Pavement Design Procedure VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 11-R6 • 2010 The implementation of mechanistic-empirical pavement design requires mechanistic characterization of pavement layer materials. The subgrade and base materials are used as unbound, and their characterization for Virginia sources was considered in this study as a supplement to a previous study by the Virginia Transportation Research Council. Resilient modulus tests were performed in accordance with AASHTO T 307 on fine and coarse soils along with base aggregates used in Virginia. The degree of saturation as determined by moisture content and density has shown significant influence on the resilient behavior of these unbound materials. The resilient modulus values, or k-values, are presented as reference for use by the Virginia Department of Transportation (VDOT). The results of other tests were analyzed for correlation with the results of the resilient modulus test to determine their use in estimating resilient modulus values. The results of the triaxial compression test, referred to as the quick shear test in AASHTO T 307, correlated favorably with the resilient modulus. Although the complexity of such a test is similar to that of the resilient modulus test for cohesionless coarse soil and base aggregate, fine cohesive soil can be tested with a simpler triaxial test: the unconfined compression test. In this study, a model was developed to estimate the resilient modulus of fine soil from the initial tangent modulus produced on a stress-strain diagram from an unconfined compression test. Full-text of this report ia available for free download (272 KB) from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r6.pdf
Item 13 Examination of an Implemented Asphalt Permeability Specification VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 11-R7 • 2010 Much research had been conducted and reported regarding the permeability of asphalt mixtures in Virginia. Because of the susceptibility of many mixtures to the entrance of water, a new permeability specification for approval of asphalt job mixtures was implemented by the Virginia Department of Transportation (VDOT) in 2005 in an attempt to eliminate permeable mixtures. A testing program was conducted during the year of implementation to examine the effectiveness of the new specification, and those results are reported herein. The purpose of the study was to determine if the contractors had to change the mixture designs so that the mixture would comply with the new permeability requirement and whether the specification produced pavements with acceptable permeability. Contractors were asked to indicate voluntarily whether mixture designs had to be redesigned because of permeability issues. In addition, each district materials engineer in the nine VDOT districts was asked to sample and test at least two surface mixtures to determine the level of permeability being achieved in the pavement. Some mixtures had to be redesigned in 2005 to comply with the new specification. Generally, pavements that had been designed in accordance with the new specification and complied with density specifications had satisfactory permeability. The new specification appears to be performing as intended, and no changes are needed. As a consequence, the results of this research were implemented. Full-text of this report ia available for free download (121 KB) from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r7.pdf _______________________________________________________________________________________________
Research and Technology Implementation Office
June 2011
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Research Digest Item 14 Best Practices in Traffic Operations and Safety, Phase II : Zig-zag Pavement Markings VIRGINIA TRANSPORTATION RESEARCH COUNCIL (VTRC)
VTRC 11-R9 • 2010 The Washington and Old Dominion (W&OD) Trail is a 45-mile multiuse trail that spans the Virginia counties of Fairfax and Loudoun. The more than 70 highway crossings of the trail create a significant potential for serious crashes between vehicles and bicyclists/pedestrians. In an attempt to increase safety at two of the crossings, VDOT installed zig-zag pavement markings in Loudoun County where the trail crosses Belmont Ridge Road and Sterling Boulevard. This study assessed the effectiveness of the zig-zag pavement markings. Effectiveness was defined as: (1) an increase in motorist awareness in advance of the crossing locations; (2) a positive change in motorist attitudes; and (3) motorist understanding of the markings. Motorist awareness was assessed by before and after speed studies. Motorist attitudinal changes were assessed through a survey targeting motorists, pedestrians, and bicyclists familiar with the markings. The survey was distributed via links posted on the Loudoun County government office website and electronic newsletters distributed by the Broad Run and Sterling District supervisors’ offices (respective districts for Belmont Ridge Road and Sterling Boulevard). Links were also distributed to bicycle clubs operating throughout the Northern Virginia area. Motorist understanding was assessed through a hand-out survey in a different region of the state that targeted motorists unfamiliar with the zig-zag marking installation in Loudoun County. Full-text of this report ia available for free download (3 MB) from: http://www.virginiadot.org/vtrc/main/online_reports/pdf/11-r9.pdf
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Research and Technology Implementation Office
June 2011
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