Vichika Iragavarapu

Driver performance at high speeds using a simulator

The goal of a Texas Department of Transportation project was a better understanding of driver performance at high speeds. Because of limited opportunity to study high-speed driving, one of the approaches used in the study was a driving simulator. The objective of the study was to measure how long drivers took to notice and react to a lead vehicle decelerating. Conditions that varied were initial speed, lead vehicle type, lead vehicle deceleration rate, and workload level. The recorded simulator data provided the research team with the drivers actual proximity to the lead vehicle at each time increment. Findings from this study included the following: higher initial speeds were associated with statistically significant longer reaction times; reaction times when following a smaller vehicle (a car in this experiment) were longer than those when following a large vehicle (a truck); brake reaction times were shorter with faster deceleration rates; and greater headways present at the start of a deceleration event were associated with longer reaction times.

High-Beam Usage on Low-Volume Rural Roads in Texas

This study evaluated high-beam usage on low-volume roadways in Texas. Most previous studies used a subjective approach to determine high-beam usage that involved a stationary observer or an observer driving around the study section. For more efficient data collection, this study used photometric readings as the methodology. This approach allowed for a quantitative measure of high-beam use, in that it did not rely on an observers opinion as to whether the headlamps were on high or low beam. Preliminary data collection was conducted as part of the study to estimate the threshold high-beam illuminance value; these illuminance data showed moderate use of high beams on low-volume, rural two-lane highways, with 42% of the free-flow drivers using high beams. There was a wide variation in high-beam use between sites, so site characteristics were reviewed to identify potential reasons for this variation. The data were fit to a logistic regression model to estimate the impact of various site characteristics on a drivers decision to use high beams. The results showed that vehicle speed, paved surface width, number of access points within 1,000 ft of the site, and presence of horizontal curves within 1 mi of the site were statistically significant factors that contributed to the probability of high-beam use. The results also showed that higher vehicle speeds, narrow paved surfaces, presence of horizontal curves, and few or no access points led to a higher probability of high-beam use. These results are intuitive and support the observations made in the exploratory data analysis.

Determining Level of Service on Freeways and Multilane Highways with Higher Speeds

The Highway Capacity Manual provides a means for evaluating level of service on freeways, highways, and urban streets. Presently, the Highway Capacity Manual methodology is not able to evaluate level of service on freeways with free-flow speeds greater than 75 mph or multilane highways with free-flow speeds greater than 60 mph, and many states now have facilities with posted speed limits that exceed these free-flow speeds. Recent research, conducted by the Texas A&M Transportation Institute (TTI), developed speed prediction equations for uninterrupted flow facilities with higher posted speed limits. From these equations, this paper develops procedures for calculating free-flow speed on facilities with higher posted speed limits and develops methods for estimating level of service on freeways with free-flow speeds up to 85 mph and multi lane highways with free-flow speeds up to 80 mph. For freeways, the recommendations call for utilizing the TTI speed prediction equations to calculate free-flow speed and using the calculated free-flow speeds to determine level of service from speed–flow curves developed within this paper. For multilane highways, recommendations call for utilizing the TTI speed prediction equations to calculate base free-flow speed, which is part of the equation for calculating free-flow speed, and then using the calculated free-flow speed to determine level of service from speed–flow curves developed within this paper. To aid practitioners, step-by-step procedures are provided for applying the TTI speed prediction equations within the Highway Capacity Manual methodology.

Development of Left-Turn Lane Warrants for Unsignalized Intersections

Left-turn movements at intersections, including driveways—especially movements that are made from lanes that are shared with through traffic—cause delays and adversely affect safety. Although some left-turn warrants have been updated, many agencies still use research performed by M. D. Harmelink in the mid-1960s. Most states use procedures that are based on Harmelinks work, but several limitations have been identified. Economic analysis can provide a useful method for combining traffic operations and safety benefits of left-turn lanes to identify situations in which left-turn lanes either are or are not justified economically. This project used a benefit–cost approach to determine when a left-turn lane would be justified. The steps included simulation to determine delay savings from installing a left-turn lane, crash costs and crash reduction savings determined from safety performance functions and crash modification factors available in the Highway Safety Manual, and construction costs. Left-turn lane warrants were developed for rural two-lane highways, rural four-lane highways, and urban and suburban roadways. In addition, warrants for bypass lanes were developed for rural two-lane highways.

Review of Tribal Transportation Safety

For more than a decade, the proportion of American Indians and Alaskan Natives killed in motor vehicle–related crashes (per population of 100,000) has been much higher than that of other ethnic groups in the United States. Between 1975 and 2002, the number of fatal motor vehicle crashes increased by 52.5% on Indian reservations, while the number declined by 2.2% nationally. Seat belt underuse, child seat restraint underuse, and operation of a motor vehicle under the influence of alcohol have been identified as key concerns for tribal transportation safety during various tribal safety summits and in the published literature. Without detailed data, identifying specific risk factors and developing effective solutions (as well as securing federal and state funding for safety programs) is difficult. This report summarizes the information available on crashes in tribal communities to generate a fact-based understanding of the status of transportation safety within these communities. Gaps in crash data and a study procedure to overcome these gaps are discussed to understand and work better to improve transportation safety on tribal lands. Results showed that readily available information could provide only a broad overview of the status of tribal transportation safety. For the major transportation safety concerns within a tribal community to be identified and addressed, data need to be obtained at the community level. For crash patterns and best practices to be identified, information should be aggregated from tribes that have successfully established a data collection procedure and have implemented safety programs.

Potential MUTCD Criteria for Selecting the Type of Control for Unsignalized Intersections

The 2009 Manual on Uniform Traffic Control Devices (MUTCD) includes guidance for the use of various types of traffic control at unsignalized intersections. Despite changes and advances in traffic engineering in recent decades, the MUTCD content related to selection of traffic control in Part 2B has seen only minor changes since 1971. In an effort to update the MUTCD, this research addressed the following types of unsignalized traffic control: no control, yield control, two-way stop control, and all-way stop control. The research team developed recommendations using information available from reviews of existing literature, policies, guidelines, and findings from an economic analysis, along with the engineering judgment of the research team and panel. The language proposed for the next edition of the MUTCD for unsignalized intersections developed at the conclusion of this research is provided in the appendix. It includes consideration of high-speed (rural) and low-speed (urban) conditions along with the number of legs at the intersection. Because the number of expected crashes at an intersection is a function of the number of legs, the decision on appropriate traffic control should also be sensitive to the number of legs present. The proposed language includes introductory general considerations, discusses alternatives to changing right-of-way control, and steps through the various forms of unsignalized control from least restrictive to most restrictive, beginning with no control and concluding with all-way stop control. Supplemental notes are provided to suggested additions to the current text, which show the reader the source(s) of the material and/or the research team’s reasoning for proposing the text.

Analysis of Expected Crash Reduction Benefits and Costs of Truck-Mounted Attenuator Use in Work Zones

A truck-mounted attenuator (TMA) is a device that attaches to the back of a work truck to help protect work crews and the traveling public from the severe consequences of rear-end crashes between motorists and slow-moving or stopped work vehicles. Although TMAs have been used by most highway agencies and contractors for many years, there are few data on the actual in-field performance of TMAs and on reductions in crash costs attributable to their use by agencies and contractors. Such data would be useful in establishing criteria on when and where TMAs must be used. An analysis of potential rear-end crashes of motorists with work vehicles in mobile and short-duration operations found that TMAs were highly effective in reducing the severity of rear-end crashes and the costs of crashes. Each crash involving a TMA resulted in a savings of

Characteristics of Texas Pedestrian Crashes and Evaluation of Driver Yielding at Pedestrian Treatments

196,855 in crash costs relative to the costs that would have been incurred had no TMA been present. On the basis of current TMA prices, agencies can recoup the cost of the TMA in terms of reduced rear-end crash costs in less than a year of daytime work shifts on facilities serving 20,000 vehicles per day or more and of nighttime work shifts on facilities serving 50,000 vehicles per day or more.