Alabama Department Of Transportation Research Articles

Case Study on Using Warm Mix Asphalt at Reduced Production Temperatures for Balanced Mix Design

This study provides a case study to illustrate the feasibility of using warm mix asphalt (WMA) at lower production temperatures to design asphalt mixtures with balanced rutting and cracking resistance in a laboratory setting. Two balanced mix design (BMD) modification approaches were evaluated to modify an existing Superpave mix design with unbalanced performance because of inadequate cracking resistance: (1) adding asphalt binder and (2) using WMA with a surfactant-based chemical additive. The modified mix designs were tested with the indirect tensile asphalt cracking test and high-temperature indirect tensile strength test to determine compliance with the Alabama Department of Transportation’s (ALDOT’s) BMD performance requirements. The original and modified mix designs were then tested in the modified overlay test to characterize their reflective cracking resistance, and the results were input into the Texas Asphalt Concrete Overlay Design System (TxACOL) software for theoretical asphalt overlay design simulations. Finally, asphalt binder testing was conducted to determine the impact of BMD modifications on the rheological properties of extracted binders. Laboratory testing showed that both BMD modifications improved the cracking resistance of the mix design but through different mechanisms. All the modified mix designs met ALDOT’s BMD requirements with balanced rutting and cracking resistance at their corresponding optimum binder content (OBC), which was 0.4%–0.7% higher than the volumetric OBC, respectively. TxACOL simulations showed that BMD modifications significantly improved the predicted reflective cracking performance and service life of asphalt overlays, but the improvement varied depending on the underlying pavement and traffic conditions.

Evaluating the impacts of vehicle-mounted Variable Message Signs on passing vehicles: implications for protecting roadside incident and service personnel

This study aims to evaluate the Variable Message Signs (VMS) mounted over the cab of emergency vehicles as a safety countermeasure to protect roadside incident and service personnel. The research team collaborated with the Alabama Department of Transportation’s Safety Service Patrol (SSP) program, specifically the Alabama Service Assistance Patrol (ASAP) in the West Central Alabama region, to collect video data from their service vehicles. Deep learning techniques were employed to detect vehicles in the recorded videos. A total of 11,338 passing vehicles were detected in 135,946 frames of video footage, and their trajectories were extracted for analysis. The study focused on examining the behaviors and movements of passing vehicles, including their speed and lane change behaviors, and developed statistical models to systematically investigate the impact of VMS on these behaviors. Random intercept models were utilized to account for unobserved factors associated with different stop locations. The modeling results revealed significant relationships between the use of VMS and the behaviors of passing motorists. When the VMS was active, drivers were more likely to change lanes and reduce their speed compared to situations where the VMS was not active. The odds of a vehicle changing lanes were found to be 95% higher when the VMS was in use. These findings suggest that the utilization of VMS can have a positive impact on traffic, particularly for passenger vehicles. The study outcomes imply that the use of VMS could be an effective countermeasure in protecting roadside incidents and ensuring the safety of service personnel.

Heat Waves and Road Traffic Collisions in Alabama, United States

The effects of heat waves on traffic collisions require investigation to improve traffic safety during extreme heat events. A time-stratified case-crossover design was used to examine associations between heat waves and traffic collisions in Alabama between May and September from 2009 to 2018. We derived a heat wave index, defined as the daily mean temperature greater than the 95th percentile for two or more consecutive days, by meteorological data from Phase 2 of the North American Land Data Assimilation System. We obtained traffic collision records from the Alabama Department of Transportation. A nonsignificant and negative association between traffic collisions and heat waves was noted, with a 1.4 percent decrease (95 percent confidence interval [CI] [−3.1 percent, 0.4 percent]) in traffic collisions on heat wave days compared to non–heat wave days. Similar results were found when the analysis was stratified by driver-related factors (i.e., gender, age, race, employment status, and driver residence distances), vehicle-related factors (i.e., vehicle usage), and collision-related factors (i.e., rural or urban roads, speed limits, and intersections). A significant and positive association was observed on heat wave days without precipitation, however (23.5 percent increase; 95 percent CI [7.3 percent, 42.3 percent]). In conclusion, traffic collisions were not associated with heat waves in many collision-related conditions in Alabama.

A comparative analysis of freeway crash incident clearance time using random parameter and latent class hazard-based duration model

The effects of freeway incident clearance times on the flow of traffic have recently increased interests in understanding what factors influence incident durations. This has particularly become topical due to the financial and economic implications of traffic gridlocks caused by freeway incidents on industries and personal mobility. This paper presents two advanced econometric modeling methods, random parameters duration modeling and latent class duration modeling in understanding the factors that impact freeway incident clearance times in the State of Alabama. These two modeling approaches were further compared to identify which of them provides the best fit for the data with respect to accounting for unobserved heterogeneity. A total of 2206 freeway crash incident data from January 1 to December 31, 2018 were examined in developing the models. The study was based on a unique dataset that involved merging and matching Traffic Incident Management response data from the Alabama Department of Transportation (ALDOT) Traffic Management Center (TMC), freeway crash data from the Center for Advanced Public Safety (CAPS) at the University of Alabama, Alabama Service and Assistance Patrol (ASAP) data from ALDOT and traffic volume from ALDOT’s Highway Performance Management System (HPMS). The model estimation results reveal that a total of nineteen variables were found statistically significant with five random variables (on-road, nighttime, rain, AADT, and ASAP existing coverage area) and fourteen fixed effects variables for the random parameters model. For latent class model, a total of eighteen variables were observed statistically significant within two distinct latent classes (Latent Class 1 with class membership probability of 0.23 and Latent Class 2 with class membership probability of 0.77) at a 0.05 significance level. A comparison of the two models reveals that the latent class model provides the better fit for the incident duration data. The findings of this study are expected to contribute to the body of knowledge on incident duration by employing two advanced econometric modeling methods and to inform statewide efforts in significantly reducing the duration of freeway incident clearance time. Moreover, this is to ensure that policy decisions that may arise from the findings of the study are sound and based on data-driven evidence.

Protocol to Assess the Impact of Crude Oil Price Fluctuations on Future Asphalt Prices

It is clear for the transportation industry that asphalt prices are heavily affected by changes in the crude oil market. This occurs because asphalt is a byproduct of the process of refining crude oil. However, there is still a lack of research on assessing the economic implications of this relationship. This paper assesses those implications through an innovative statistical process designed to quantify the economic correlation between asphalt and crude oil price fluctuations in Alabama. The proposed statistical process is used in this paper to model the relationship between the Alabama Department of Transportation’s (ALDOT’s) monthly asphalt price index and a national crude oil index published by the US Energy Information Administration. The process quantifies the relationship between these two commodities in relation to two metrics: (1) the time gap between an observed change in the crude oil index and its corresponding impact on the asphalt price index and (2) the magnitude of that impact. It was found that the most likely time gap between crude oil and asphalt price fluctuations in Alabama is 3 months, with a change ratio of 0.58. This means that a 1% increase in the price of crude oil would most likely affect the Alabama asphalt market 3 months later with a price increase of about 0.58%. Recognizing that these are just average values, the paper also presents a risk assessment tool that provides ALDOT with the probability of occurrence of different scenarios taking into consideration the observed variability in time gaps and change ratios.

Friction and Texture Retention of Concrete Pavements

In the late 1980s and early 1990s, the Alabama Department of Transportation (ALDOT), U.S., noticed a decline in skid trailer numbers on concrete pavements shortly after grinding operations. The engineers at the time suspected that the coarse aggregate caused the decline in these numbers and the resulting conclusion led to a ban of carbonate aggregates in mainline concrete pavement in Alabama that is still in place. This detailed laboratory study re-examines the fundamental friction issues that led to this policy. A total of 48 aggregate, grinding, and grooving combinations were tested as part of this study. Three aggregate sources were examined: a siliceous source, a “hard” limestone source, and a “soft” limestone source. Two blade spacings were examined for grinding operations: 52 blades/ft and 60 blades/ft. Some ground specimens were also grooved. Finally, a set of specimens had the Next Generation Concrete Surface (NGCS) applied to them. The specimens were polished with the National Center for Asphalt Technology (NCAT) three-wheel polishing device (TWPD). The dynamic friction tester was used to evaluate friction values at various points through the polishing process. After the polishing, the macrotexture was characterized using the circular track meter. Across the board, the highest performing texture was that with no grooves and 52 blades/ft. Very generally, the loss of friction decreased with increasing siliceous content. However, some of the trends were extremely minor and, in a few cases, siliceous aggregates caused higher friction loss. There were numerous instances when blended carbonate/siliceous concrete pavement surfaces performed better than sole siliceous concrete pavement surfaces.

Assessing Work Zone Traffic Control Options for 3-to-1 Lane Closures

The presence of highway construction zones hinders mobility and affects traffic operations. A 2002 study by Wunderlich & Hardesty reported that nearly 20% of the National Highway System roads have scheduled construction work during the peak construction season. Additionally, approximately 24% of non-recurring delays on freeways are caused by work zones. To minimize time lost by travelers due to work zone induced traffic congestion, it is important to efficiently plan temporary traffic control (TTC) at work zones. Earlier research conducted by Sisiopiku & Ramadan, 2017 confirms that the majority of State Departments of Transportation currently rely on their earlier experience when planning for work zones, rather than consider operational and safety impacts. Using a study corridor in Birmingham, Alabama as a test bed, this study investigated the operational impacts of TTC options for work zones with 3-to-1 lane drop configuration using traffic data collected from the Alabama Department of Transportation. The VISSIM simulation platform was used to conduct the experiments. The experimental design considered two TTC strategies (i.e., static late and early merge) under 3-to-1 lane drop configuration for work-space length of 500 ft for long- and short-term lane closures. The study concluded that the 3-to-1 lane-drop configuration should not be scheduled for long-term duration. Maintenance work can be scheduled from midnight to early morning and under the 3-to-1 lane closure scenario the performance of early and late merge traffic control is similar. Overall, this study used simulation modeling to compare the effectiveness of two traffic control strategies at work zones on the basis of different performance measures. The results provide information about the impact of each control strategy on density, speed, travel time etc. They also help determine what time of the day is best for lane closings in order to reduce adverse impacts from capacity reduction. Thus, the findings are expected to provide valuable guidance for agencies responsible for planning, design, and operations of work zones in the future.

Access Control Techniques to Mitigate Wrong-Way Driving Activities on Multilane Divided Highways: Case Studies in Alabama

This paper documents the results of a second phase statewide research project on wrong-way driving (WWD) crashes funded by the Alabama Department of Transportation. The purpose of this effort is to investigate why people drive in the wrong direction on the multilane divided highways in Alabama. The field data were collected at locations where there were WWD crashes or incidents over 5 years. Video cameras were used to monitor the WWD activities for 48 h from Friday to Sunday. The WWD activities were analyzed by the research team watching the video data. The study found that drivers tend to drive in the wrong direction as a result of driveways with a close median opening, poor front access control, lack of backage road connection, and limited sight distance because of large median widths or grade difference. The study also found that there is a high frequency of intentional WWD at some access points connecting gas stations, business, and residential areas on divided highways. It is recommended that access management techniques are applied to mitigate WWD activities on divided highways based on four case studies, including (1) providing closer exclusive U-turn median openings for indirect left turns; (2) improving poor front access control, for example installing a channelized island for right-in and right-out driveways; (3) providing backage road connections for close mixed land use; and (4) improving sight distance for minor-road traffic at unsignalized intersections with large grade difference or wide median widths.

Development of a slope failure database for Alabama highways

Slope stability management systems (SSMSs) have been developed by multiple state transportation agencies to assess landslides adjacent to highways and aide in the effective allocation of resources for slope and/or roadway repairs. SSMSs catalog and analyze slope failures through the use of three main components: a landslide data collection system, a geographic information systems (GIS) database, and a hazard prioritization system. The components form a landslide management system used for the identification or prediction of landslide risk areas and the determination of landslide hazards to motorists. The Alabama Department of Transportation (ALDOT) has not previously employed a SSMS, which limits the ability of ALDOT engineers and geologists to effectively manage landslide hazards along highways. This paper discusses the development of a landslide collection system and database developed to improve the ability of ALDOT to identify common causes and locations of slope failures along Alabama highways. The collected data were converted into a GIS database, which allows for correlations between landslides and additional spatial data, such as average precipitation and surface geology. This paper presents a brief review of similar SMSSs, reviews the proposed database, and discusses preliminary observations. The data collected from this study can be used to identify common causes of landslides along Alabama highways and select efficient remediation options.

Development of a Hot Mix Asphalt Location Cost Index for the Alabama Department of Transportation

Asphalt is one of the most critical commodities for the U.S. infrastructure. It is used as a paving material on the majority of roadways across the country. In Alabama, this material is used in approximately 98% of all paved roads, consuming about 40% of the Alabama Department of Transportation (ALDOT) annual construction budget. Because of the considerable importance of this material, any improvements in ALDOT’s hot mix asphalt (HMA) cost-estimating procedures are expected to be reflected in better budget control and a more effective use of ALDOT’s limited available resources. This paper presents a HMA Location Cost Index (LCI) intended to contribute to ALDOT’s efforts toward the improvement of its cost-estimating practices. This is an annual LCI aimed to quantify changes in HMA prices among three geographic regions in Alabama: north, central, and south regions. The development of the LCI involved the use of advanced data collection, cleaning, and processing techniques to analyze historical bid data from 3661 projects awarded by ALDOT between 2006 and 2016. The potential contribution of the proposed LCI to improving ALDOT’s current cost-estimating system is demonstrated via statistical significance testing and through the application of an innovative moving-window cross-validation algorithm previously developed by the authors.

Five-Year Performance of Improved Open-Graded Friction Course on the NCAT Pavement Test Track

Open Graded Friction Course (OGFC) mixtures are used as the final riding surface on roadways as they offer many benefits, such as reducing hydroplaning, reducing splash and spray behind vehicles for improved driver visibility, improving wet-pavement friction, and reducing surface reflectivity during wet-weather conditions. Despite these benefits, the use of OGFC has diminished over the years due to durability and service-life issues. The typical OGFC pavements in Alabama have exhibited premature distresses (e.g., raveling) after approximately six or seven years in service. Therefore, there is a need to change the current OGFC mix design procedure to improve the mix durability. In this study, three modified OGFC mixtures were designed based on a 12.5-mm OGFC mix design previously approved by the Alabama Department of Transportation (ALDOT) and paved in three test sections (E9A, E9B, and E10) on the National Center for Asphalt Technology pavement test track to evaluate possible changes to ALDOT’s OGFC mix design procedure. The ALDOT-approved mix design lasted less than 20 million equivalent single-axle loads (ESALs) on I-85, a few miles from the test track, whereas the three modified OGFC mixtures lasted more than 20 million ESALs and remained in place for another research cycle (10 millions ESALs) on the test track. The three modified OGFC mixtures also showed improved laboratory performance characteristics compared with those of the ALDOT-approved OGFC mixture. Based on the field and laboratory test results, adjustments made in the three modified OGFC mixtures can potentially improve the long-term field performance of OGFC mixtures in Alabama.

Full-Scale Performance Evaluations of Various Wire-Backed Nonwoven Silt Fence Installation Configurations

Silt fences have long been a key component for controlling construction stormwater runoff; nonetheless, many silt fence installations fail to perform in the field as intended. Silt fences are temporary sediment control measures used to retain sediment by impounding runoff and allowing for sedimentation on-site, while simultaneously discharging stormwater runoff at a controlled rate. This study evaluated the performance of eight alternative configurations of the Alabama Department of Transportation (ALDOT) standard wire-backed, nonwoven silt fence. Standard installation parameters associated with the ALDOT silt fence include (1) 32-in. (81.3-cm) high fence, (2) 0.95 lb/ft (1.4 kg/m) support T-post, and (3) 10 ft (3.0 m) T-post spacing. Throughout the series of configurations tested, these standard parameters were varied individually and jointly in efforts to improve overall performance. Variations to the standard parameters include (1) 24-in. (61.0-cm) high fence, (2) 1.25 lb/ft (1.9 kg/m) support T-post, (3) 5 ft (1.5 m) T-post spacing, and (4) trench offsetting. Performance analyses were conducted on each configuration and results were evaluated to determine the best overall configuration to enhance the in-field performance of the ALDOT silt fence. Ultimately, the offset 24 in. (61.0 cm) fence with 1.25 lb/ft (1.9 kg/m) T-post spaced 5 ft (1.5 m) on-center resulted in the best overall improvement, retaining an average of 93% of sediment and deflection of only 0.18 ft (0.004 m) over the course of three simulated storm events.

Experimental and analytical investigation of end zone cracking in BT-78 girders

In the past decade, with a growing interest in long span bridge girders, designers are using an increasing number of prestressing strands. This scaling up has led to cracking issues in the end zone of narrow stemmed bulb-tees and I-girders, impacting the service life and possibly design capacities in case of excessive cracking. In a project funded by the Alabama department of transportation (DOT), a 180ft long girder design was developed by modifying a standard Bulb-Tee girder and using a 10 ksi self-consolidating concrete mix. The new girder is 78in. deep and has 66–0.6in. strands. The impact of the draping angle and debonding on the end zone cracking was first evaluated using a 3D finite element model (FEM) developed in ABAQUS. Subsequently, the critical stresses were monitored during the detensioning process of four 54ft long full-scale girders with different end zone details. It was found that the combination of limiting the draping angle and debonding the strands resulted in minimizing the end zone cracking. The detailed FEA model which was developed is also verified using experimental field data. The results of this experimental and analytical investigation will be presented in this paper.

Performance Evaluations of Three Silt Fence Practices Using a Full-Scale Testing Apparatus

Erosion and sediment controls on construction sites minimize environmental impacts from sediment-laden stormwater runoff. Silt fence, a widely specified perimeter control practice on construction projects used to retain sediment on-site, has limited performance-based testing data. Silt fence failures and resultant sediment losses are often the result of structural failure. To better understand silt fence performance, researchers at the Auburn University-Erosion and Sediment Control Testing Facility (AU-ESCTF) have evaluated three silt fence options to determine possible shortcomings using standardized full-scale testing methods. These methods subject silt fence practices to simulated, in-field conditions typically experienced on-site without the variability of field testing or the limited application of small-scale testing. Three different silt fence practices were tested to evaluate performance, which included: (1) Alabama Department of Transportation (ALDOT) Trenched Silt Fence, (2) ALDOT Sliced Silt Fence, and (3) Alabama Soil and Water Conservation Committee (AL-SWCC) Trenched Silt Fence. This study indicates that the structural performance of a silt fence perimeter control is the most important performance factor in retaining sediment. The sediment retention performance of these silt fence practices was 82.7%, 66.9% and 90.5%, respectively. When exposed to large impoundment conditions, both ALDOT Trench and Sliced Silt Fence practices failed structurally, while the AL-SWCC Trenched Silt Fence did not experience structural failure.

Contraflow evacuation e-planning system for I-65 in Alabama

Contraflow on major evacuation routes is one approach that has been adopted in many Gulf Coast states for hurricane evacuation. The idea is to reverse one direction of the roadway to accommodate the often substantially increased travel demand moving away from the impact area. Efficient planning and operation is critical to a successful contraflow implementation. The purpose of this paper was to develop a decision support system for contraflow evacuation planning for use by the Alabama Department of Transportation (ALDOT). User requirements were identified, and a literature review was conducted to determine applicable existing algorithms. A working prototype system was then constructed. The practical value of this paper is to provide state transportation officials with an effective computer-based tool for pre-planning and evaluating possible responses to such an event.

Evaluation of Wheat Straw Wattles for Velocity Reduction in Ditch Check Installations

Linear construction typically uses drainage conveyances to convey storm-water runoff away from construction sites to neighboring water bodies. These conveyances may be unstabilized and highly susceptible to erosive shear stresses associated with high-velocity flow. In certain situations, wattle ditch checks are used to help reduce channel erosion caused by high-velocity flow by creating an impoundment. However, with new technology emerging and limited scientific data available on the in-field performance of wattles, the quantification of an installation's effectiveness for improving runoff control is difficult. The effectiveness of various configurations of wattle ditch check installations was investigated at the Auburn University Erosion and Sediment Control Testing Facility to help the Alabama Department of Transportation (DOT) improve the performance of wattle ditch checks. Results indicate that Alabama DOT's current installation practice of staking a wattle only to an unstabilized channel can be improved. The addition of a filter fabric underlay protects the channel bottom from scour at the installation area, and the use of sod staples coupled with a teepee staking pattern secures the wattle in place and increases ground contact, which reduces undercutting. This configuration ultimately minimizes highly erosive supercritical flows and maximizes the subcritical flow length by 99% compared with the base installation.

Data Development for Implementing Integrated Land-use and Transportation Forecasting Models in Medium-sized Metropolitan Planning Organizations

Integrated land-use and transportation forecasting models require large amounts of data to calibrate and estimate. Obtaining reliable datasets for these models can be one of the most cost-prohibitive and time-consuming stages of such an endeavor. The purpose of this paper is to present a case-study data development program that was able to successfully provide all of the needed data for the estimation and calibration of an integrated land-use and transportation forecasting model. The recently developed Cube Land model was implemented in the Montgomery (Alabama) Area Metropolitan Planning Organization with funding from the Alabama Department of Transportation. The data development program was fiscally and temporally constrained and replicates typical model development conditions in medium-sized metropolitan planning organizations. This case study presents findings demonstrating that in the US locally developed datasets combined with national data sources and ‘off-the-shelf’, relatively low-cost but high-quality, purchasable datasets can be obtained in a relatively short amount of time and are sufficient to estimate and calibrate an integrated land-use and transportation forecasting model.

A Web-Based Geotechnical GIS

A web-based Geotechnical Geographic Information System (GeoGIS) was developed and tested for the Alabama Department of Transportation. This web-based system stores geotechnical information about transportation projects, such as subsurface data, construction drawings, and design information. Typically, this information is in a report or plan sheet format, but raw geotechnical data can also be accommodated in the GeoGIS. The goal of this system is to provide easy access and storage for all geotechnical and subsurface structural information from across a state. Access through a secure web interface allows for keyword searches and interactive map selection. The web-based GeoGIS has four geotechnical layers (project, bridge, foundation, and soil boring) that can be displayed on a road map, aerial photos, or USGS 7.5 minute quadrangles. For testing purposes the GeoGIS was populated with multiple document types, formats, and sizes. In all cases, the system performed above expectations.

Robust Determination of Liquidated Damage Rates for State Highway Agencies

Liquidated damages (LDs) in highway construction contracts are daily monetary rates meant to compensate the owning agency for additional costs incurred because a project did not meet its completion date because of contractor delay. When LD provisions are challenged in court, provisions that lack proper documentation outlining the procedure used to determine rates have been deemed a penalty and unenforceable. This research effort sought to develop a methodology for developing a schedule of LD rates to be adopted by the Alabama Department of Transportation (ALDOT). The procedure outlined is to be used periodically to review and update the LD rates found in ALDOT's standard specifications for highway construction contracts, since their current schedule and review procedure has come under legal scrutiny. A statistically justifiable procedure was developed to calculate LD rates using historical project cost accounting data to create a traditional provision based on FHWA guidelines with the LD rates stipulated in a contract-size categorized table. The proposed procedure was then compared with a typical procedure used for developing LD rates. After comparisons, the proposed procedure stipulating LD rates in a table by contract value was determined to be the more robust method. The final product of this research is stepwise guidelines for practitioners to use on a periodic basis to review and update their schedule of LD rates.

Screening Tool to Assess Adequacy of Bridge Pile Bents during Extreme Flood/Scour Events

A common design/construction procedure for highway bridges in Alabama is the use of steel HP piles driven to a firm stratum with a length above ground up to the level of a concrete bent cap which supports the bridge superstructure. The use of three, four, five, or six such piles in a row with the two end piles battered are very common bridge pile bents. Because of the large number of bridges in the state and the tendency to use standardized designs with pile bent substructures, the Alabama Department of Transportation recently developed a “screening tool” to assist its engineers in assessing the adequacy of bridge pile bents for extreme flood/scour events. The evaluation procedure employed in the screening tool is presented in macro and microfloodchart form in this paper, and basically moves through the following sequence: (1) preliminary or general checks such as the bridge bent being located in water with scour possible, etc.; (2) checking the bent piles for possible “kick-out” or plunging failure; (3) ...