Field Validation of Equivalent Modulus for Stabilized Subgrade Layer

This report presents the findings associated with an effort to evaluate projects with weak subgrades utilizing the newly developed Equivalent Modulus Analysis (EMA) spreadsheet created by the Louisiana Department of Transportation and Development (DOTD). The EMA spreadsheet was developed to simplify the design process by allowing for easy application of the Method of Equivalent Thickness (MET) calculations that lies at the heart of the pavement design process. A validation was attempted by trying to compare the EMA spreadsheet\u2019s predictions to field collected data. Lime treatment projects were used to do the assessment as lime treatment is often employed in establishing working tables for construction equipment that cannot operate on very weak subgrades. This research attempted to accomplish two objectives: (1) to try to find a way to incorporate lime treatments into the design process in order to take advantage of the strength it offers and (2) to explore the strengths and weaknesses of the MET approach used in the design process through utilization of the EMA spreadsheet to see if there is a way to assess weak subgrades. Results, however, were both inconclusive and questionable because the untreated and lime-treated soils typically sheared during field testing which invalidated back-calculation efforts. Additionally, it proved problematic to assume that raw subgrades could be held as two-layer systems in order to carry out back-calculation. As such, the EMA spreadsheet could not be validated. More testing would be required to validate the approach

Maintenance of Roadway Edge Drop-Off Utilizing Readily Available Materials

LTRC Project Number: 19-1GTSIO Number: DOTLT1000The Louisiana Department of Transportation and Development (DOTD) District 05, which is in the northeastern corner of the state, spent 55,000 hours and over $1 million in 2016 attempting to maintain roadway edges along non-paved shoulders. Non-paved shoulders consist primarily of a soil and aggregate mixture, which is routinely disturbed and lost under normal traffic conditions primarily at the paved roadway edge. This problem is more prevalent on narrow winding roadways where the wheel path meanders closer to the edge of the roadway. Tires disturb this material leaving a drop-off (edge rut) that requires continuous maintenance and can be unsafe to the traveling public. The means and methods used to maintain non-paved shoulders statewide varies with undocumented performance. Reclaimed asphalt pavement (RAP) is readily available and used in many areas of the state for shoulder repair. Some parish maintenance units use 100% RAP while others use a mixture of native soils blended to local proportions. Although RAP is common among DOTD district offices, it needs a binder to help stabilize the often-rounded aggregate particles within. In so, additives (such as cement, fly ash, soil, and asphalt emulsion) can improve RAP strength and stability. Mix 1 (75% RAP and 25% lean clay) with an additive of 4% to 6% cement was successful in both feasibility (amount of material utilized by volume) and performance (strength and durability of test samples)

Evaluating Permitted/Protected Versus Protected Left-Turn Signals in Louisiana

DOTLT1000378The main objective of this study is to evaluate the safety and operation of existing left-turn signal phases at intersections and investigate relevant data to develop proper guidance on when it is appropriate to install each signal type. The study considered protected-only (PO), protected permitted left-turn (PPLT), and flashing yellow arrow (FYA) left-turn phases for the evaluation. The study was conducted in four different folds \u2014 nationwide survey, decision tree modeling, safety analysis, and operation analysis. The nationwide survey revealed that the majority of the respondents indicated FYA as the preferred left-turn signal in terms of operation, followed by PPLT. At the same time, from a safety perspective, PO was desired, followed by FYA. The decision tree revealed several factors such as total left-turn crashes, median types, number of left-turning lanes, speed limit, and annual average daily traffic (AADT) controlling the selection of PO over PPLT. The safety analysis showed almost double left-turn crashes per year at PPLT compared to PO and FYA intersections. Crash modification factor (CMF) of PO over PPLT for total crashes showed that PO was only able to reduce fatal and severe crashes by 25.5% compared to PPLT; however, PO was able to reduce all severe levels of left-turn crashes. It indicates that PO performs better than PPLT from a safety perspective. Before-and-after evaluation at FYA intersections revealed a left-turn crash reduction of 17.73%. In addition, delay analysis showed an average delay of 50.69 seconds per vehicle (sec/veh) at PO, 46.04 at PPLT, and 31.49 at FYA. However, the delay only during the morning peak hour at PO was significantly higher than at PPLT. At other periods, it was not. Delay at FYA was all-time low compared to PO and PPLT, but the outcome from FYA is less robust due to the limited sample size. With left-turn crash reduction by more than 50% and delays not significantly more at all times of the day, the study indicates PO performs better than PPLT. The framework from the decision tree provides key information to help select the suitable left-turn phase between PO and PPLT

Develop and Evaluate Performance Measures for Intelligent Transportation Systems (ITS) in Louisiana

The Louisiana Department of Transportation and Development (DOTD) established Intelligent Transportation System (ITS) programs over 20 years ago. Before DOTD expands or implements new ITS programs, a study needed to be undertaken to evaluate the performance of the current ITS programs to demonstrate their benefits. The primary objective of this research was to develop a set of performance measures for each existing ITS program in Louisiana and evaluate the benefits achieved through their implementation. The scope of this study was to use insights gathered from literature reviews, qualitative surveys, and inputs from stakeholders to develop performance measures for Louisiana's ITS applications. The scope also included using data from ITS applications in Louisiana to evaluate the performance of the deployed system and determine if the ITS applications were beneficial to the taxpayer. The ITS programs were grouped under six broad areas: Arterial Management; Commercial Vehicle Operation; Electronic Payment and Congestion Pricing; Freeway Management and Traffic Management Centers; and Traveler Information. For each program area, specific objectives linked to specific transportation goals that Louisiana needed to achieve were developed, along with performance measures to evaluate the state\u2019s efforts at meeting each goal. Data mainly between 2016 and 2020 were collected and used for the assessment. Overall, the benefits achieved through the implementation of some of the ITS programs were apparent, while in other cases, further studies are required

Structural Assessment of Inundated Roadways in Livingston Parish, Louisiana With the Falling Weight Deflectometer

Researchers discovered strong evidence of damage to Livingston Parish\u2019s inundated roadway system during the flood of August 2016. LTRC conducted a comprehensive structural assessment of inundated roadways in Livingston Parish, Louisiana with the falling weight deflectometer (FWD). Treated (inundated) versus non-treated (non-inundated) statistical methods were employed to prove damage. Three parameters from the FWD were used in the analysis, in-place structural number (SNeff), deflection at the first sensor of the FWD (D1), and subgrade resilient modulus (Mr). The damage was translated into an equivalent thickness of asphaltic concrete (AC) pavement from the parameter of SNeff using pavement design methods typically used by the Louisiana Department of Transportation and Development (DOTD). The data were sorted into three groups based on the thickness of the AC pavement: All data points (all thickness groups), 4 in. to 3 in. group, and 2 in. to 2.5 in. group. The statistical analysis of the entire set of data indicated that statistical differences existed for all three parameters, SNeff, D1, and subgrade Mr. Regarding SNeff, the difference between the mean values of the non-inundated and inundated roadways was equivalent to approximately 1 in. of AC. The differences in the mean values for D1 and subgrade Mr indicated that the inundated pavements were approximately 22.5 percent and 10.3 percent, respectively, weaker than the non-inundated pavements. Statistical comparisons on the 4 in. to 3 in. thickness group indicated that statistical differences existed for all three parameters, SNeff, D1, and subgrade Mr as with the all thickness group. In the case, the differences in SNeff was equivalent to approximately 2.5 in. of AC. Regarding the D1 and subgrade Mr parameters, the results indicated that the inundated pavements were approximately 56.5 percent and 25.3 percent, respectively, weaker than the non-inundated pavements. Statistical differences in the three parameters, SNeff, D1, and subgrade Mr for the 2.0 in. to 2.5 in. thickness group were not discovered; however, differences in magnitudes of the means for each parameter were discovered, all indicating that the inundated pavements were weaker than the non-inundated pavements. Regarding the SNeff, the difference in the mean values between the non-inundated and inundated pavements were equivalent to approximately 0.5 in. of AC. The difference in stiffness between the inundated and non-inundated pavements based on the D1 parameter was approximately 22.6 percent, while the strength difference in subgrade Mr was approximately 4.6 percent

Geotechnical Asset Management for Louisiana

18-4GT, 1000226This research advanced Geotechnical Asset Management (GAM) within DOTD. It describes the logic and software utilized to develop the DOTD retaining wall inventory and outlines a GAM path forward for the Department. The developed GAM GIS database provides geospatial locations, digital storage, digital rating applications, and visual interfaces for retaining walls including historical information. Inventory efforts utilized efficient and effective tools of aerial photography, mapping, and GIS software, web applications, and mobile applications. DOTD can replicate these efforts for other asset types. Researchers developed desk and mobile applications for efficient collection of condition and consequence assessment data into the GIS Database. Districts with their local knowledge should use these tools as part of the rating process. Full GAM development and implementation will provide the department a logical method to manage risk, address problematic locations, and effect a rationale to implement appropriate repairs in a timely manner

MASH TL-4 Engineering Analyses and Detailing of 36-In. And 42-In. High Median Barriers for LADOTD

23-1STDOTLT No. 1000464Single-slope median barriers are currently planned for several bridges in Louisiana. For these bridges, both 36-in. and 42-in. designs were developed and considered as part of this project. Both barrier designs can be used near a longitudinal joint that is approximately 1 in. wide. The 36-in. high barrier is similar to the single-slope traffic rail (SSTR) used by the Texas Department of Transportation (TxDOT), which was successfully crash tested according to the Manual for Assessing Safety Hardware (MASH) Test Level 4 (TL-4) in July 2010. The Louisiana Department of Transportation and Development has incorporated the TxDOT SSTR bridge rail height and profile for the median barriers planned for this project. The 42-in. high barrier maintains the same slope as the 36-in. median barrier but has a smaller top thickness. This project aimed to evaluate the strength of the proposed median barrier designs according to the American Association of State Highways and Transportation Officials Load and Resistance Factor Design (LRFD) Bridge Design Specifications for MASH TL-4 crash performance. The report presents the results of the strength analyses performed on these designs and offers recommendations for improving their strength and performance under MASH TL-4 impact conditions

Evaluate the Impacts of Complete Streets Policy in Louisiana

21-2SSDOTLT1000377The goal of Complete Streets is to accommodate all road users and bring attention to the needs of vulnerable road users. In the last 10 years, thousands of local/regional/state agencies in the United States (U.S.) have adopted Complete Streets policies. However, it is not clear how successfully these policies have been implemented and to what extent agencies have achieved related policy goals. The research team made a holistic review plan to observe the Policy\u2019s impacts on DOTD\u2019s inputs, activities, project outputs, project outcomes, and project impacts between 1/1/2011 and 12/31/2020 to evaluate whether/how Louisiana Department of Transportation and Development (DOTD) has made progress toward the adopted policy goals. Interviews and surveys were also conducted to better understand successes, barriers, and lessons learned in the first 10 years of DOTD\u2019s Complete provide potential solutions to the identified challenges. Overall, much progress has been made compared with where the state started in 2010. However, shifting agency culture to balance multimodal needs is a long-term process. The research team compiled a full list of recommended actions (in \u201cRecommendations\u201d) and highlighted those, that could potentially be done in the near term (in \u201cImplementation Statement\u201d) for DOTD\u2019s consideration

Mitigation Strategies of Reflection Cracking in Pavements

LTRC project Number: 14-4PFReflection cracking is a serious challenge associated with pavement rehabilitation. Practical experience shows that reflection cracking propagates at a rate of 1 in. per year. The primary objective of this synthesis study is to conduct an in-depth literature review of research projects on reflection cracking and a survey of the practices of highway agencies with regard to the types of cracking mitigation strategy used. Based on the results of the literature review and the survey questionnaire, a summarized assessment is presented for each reviewed treatment method. Further, a number of treatment methods were identified for further evaluation. For existing hot mix asphalt (HMA) pavements, crack sealing and overlay, chip seal and open-graded interlayers, full-depth reclamation, and cold-in place recycling are the most promising treatment methods. For existing Portland cement concrete (PCC) pavements, saw and seal, chip seal and open-graded interlayer systems, and rubblization are the most promising treatment methods. Based on the results of this study, the research team recommends that a follow-up study be conducted in order to evaluate the cost-effectiveness of the most promising treatment methods and to develop guidelines for the control of reflection cracking. The developed crack control guidelines will present recommended treatment methods for different classes of rehabilitated pavements in order to achieve adequate control of reflection cracking in a cost effective manner