bluuebunny/crossref_metadata_2025 huggingface dataset:
Operational Effects of U-Turns as Alternatives to Direct Left Turns from Driveways
Authors: Zhou Huaguo , Lu Jian , Yang Xiao , Dissanayake Sunanda , Williams Kristine M.
Published: April 2007

Recently, many state and local transportation agencies have begun considering using U-turns as alternatives to direct left turns (DLT) from driveways through installing nontraversable medians on multi-lane highways. Some of the concerns are that this proposed change may transfer operational problems to the downstream median opening and increase delay or travel time of vehicles making a left-turn egress from driveways. However, the effect of this treatment on roadway operations is not clear. A comprehensive study of operational effects of this treatment would be beneficial, both in setting design policy and in project-level design. Field studies were conducted to obtain the data necessary to quantify operational effects of this treatment at eight sites in the Tampa and Clearwater areas of Florida. About 300 h of field data were collected, including delay, travel time, traffic volume, speed, traffic control, and geometric data. An operational effects database was developed to perform statistical analyses. Delay and travel-time models of DLT and right turn plus U-turn (RTUT) were developed as a function of major and minor road-traffic-flow rates. The curves developed based on delay and travel-time models present a clear picture of the operational effects of the two types of movement. Moreover, a ratio model was developed to estimate how many drivers would prefer to make a RTUT rather than a DLT under certain traffic-flow conditions. Finally, the operations models were used to measure system performance of a full median opening versus a directional median opening from the standpoint of weighted-average total delay.
Freeway On-Ramp Design Criteria for Ramp Meters with Excessive Queue Detectors
Authors: Chaudhary Nadeem A. , Messer Carroll J.
Published: April 2007

Guidelines were developed for designing freeway on-ramps in which ramp metering is envisioned. More specifically, design issues were probed for ramps in which the ramp meter utilizes a queue detector to identify and prevent a queue of vehicles from blocking the upstream intersection. First, the benefits of ramp metering operation were delineated, and general design considerations were then drawn up. Finally, design criteria were developed for three distance requirements for freeway on-ramps: safe stopping distance, storage distance, and acceleration distance.
Intervehicle Spacings and Queue Characteristics
Authors: Long Gary
Published: April 2007

The lengths of queues of stopped vehicles are important in the design of storage bays for left- and right-turning traffic, for timing signal phases to clear queues, for simulation of traffic operations, and for other purposes. Queue lengths depend on the numbers and types of vehicles stored, the lengths of vehicles, and the spacings allowed by drivers between vehicles. The lengths of both trucks and passenger vehicles have been changing over the past two decades. On the basis of recent observations of queue component lengths, guidance was developed for estimating queue lengths for the current vehicle fleet. It was found that the 7.6 m (25 ft) per vehicle, including an intervehicle gap that is often assumed for design, and 0.915 m (3 ft) between vehicles used by CORSIM, are severe under-estimations for determining queue lengths. From observations measured at a variety of sites, intervehicle spacings were found to average 3.66 m (12 ft) and were not found to differ significantly at different sites. Models were devised for estimating average queue lengths and maximum lengths at a given probability.
Analysis of Clear-Water Scour at Bridge Contractions in Cohesive Soils
Authors: Güven Oktay , Melville Joel G. , Curry John E.
Published: April 2007

A new, simplified theory for the analysis of the time-dependent development of the depth of scour at bridge contractions in cohesive soils under clear-water conditions is presented. The new theory is an extension of the clear-water scour theory for a long contraction currently used for non-cohesive bed materials. It is based on the “scour rate in cohesive soils” concepts introduced recently by Briaud and his colleagues at Texas A&M University. A description of the simplifying assumptions made in the development of the theory and several applications with different bed soils and flow conditions are presented to illustrate the effects of various assumptions on the estimate of the scour depth. Limitations of the theory are also discussed. The results indicate that a very long time may be required in some cohesive soils for the scour depth to reach its maximum value for a given flow condition. The results also indicate that significant differences in the estimate of the scour depth may occur depending on the assumptions made about the behavior of the water surface elevation and the total head in the contraction during the development of the scour in the contraction.
Geospatial Distribution of Metal Elements in Transportation Land Use Surficial Soils
Authors: Teng Zheng , Smithson Joseph A. , Zhou Ping , Sansalone John J.
Published: April 2007

Highway traffic generates heavy metals and particulate matter through various vehicular and tire-pavement abrasion mechanisms. These abraded materials are deposited, they accumulate, and they are transported by storm water. Soils subject to years of such loading can serve as a sink and a potential source for heavy metals. The results of geotechnical analyses, heavy metal distributions, drainage influences, and correlations to geotechnical indices for surficial (0 to 15 cm) glacial till samples recovered from two transects along a heavily traveled urban interstate highway were compared with a control site subjected to only urban atmospheric deposition. This investigation indicated, for this site, that heavy metal accretion in the surficial soils is a function of depth, surface drainage patterns, distance from the pavement edge, and soil indices. Particulate-bound heavy metal deposition and accretion or export were a function of surface flow conditions such as velocity, flow depth, and surface cover. Results indicated that heavy metal accretion rapidly decreases as a function of distance from the traveled roadway. Along the longitudinal transect, correlations between heavy metals and soil organic content were statistically significant, particularly for copper. Along the transverse transect, correlations between soil plasticity, organic content, and heavy metals were statistically significant. Although there is little control of traffic levels and past accretion, indices such as soil organic content and plasticity index, as well as pavement runoff surface drainage patterns, can provide information about whether highway soils might act as a sink or source of heavy metals and, consequently, if best management practices may be justified.
Development of the Midwest Guardrail System
Authors: Sicking Dean L. , Reid John D. , Rohde John R.
Published: April 2007

A revised guardrail system has been developed that should provide greatly improved performance for high-center-of-gravity light truck vehicles. The barrier incorporates W-beam guardrail and standard W6×9 steel posts. Primary changes to the design include raising the standard rail height to 635 mm, moving rail splices to midspan between posts, increasing blockout size, and increasing the size of post bolt slots. All of these changes were designed to improve the barrier’s performance with high-center-of-gravity vehicles. One full-scale crash test was conducted to verify that the guardrail would perform adequately with mini-sized automobiles when raised to 660 mm to the center of the rail. This test proved that the barrier can provide satisfactory performance when mounted at heights ranging from 550 mm (standard guardrail height) up to 660 mm. Hence, the new guardrail design provides approximately 110 mm (4.4 in.) of mounting height tolerance. When installed at the nominal mounting height of 635 mm, a 75-mm pavement overlay could be applied to the roadway without requiring adjustments to the barrier’s height.
Vehicle Impacts in V-Shaped Ditches
Authors: Thomson Robert , Valtonen Jarkko
Published: April 2007

V-shaped ditches represent a significant portion of the roadside environment in Sweden and Finland. The consequences of vehicles leaving the road and entering V-shaped ditches are not well documented in simulation or experimental studies. A series of tests were conducted to document the behavior of passenger cars entering V-shaped ditches. Test conditions ranged from 5° to 20° and 80 to 110 km/h. The tests resulted in many vehicles passing over the backslope, and rollovers were observed in four of the tests. Preliminary simulations of the test conditions were not able to fully reconstruct the vehicle motions. Castor steering of the vehicle and ground contact with the vehicle chassis were the two most important features observed in the tests, but they were not incorporated into the simulation model.
Flared Energy-Absorbing Terminal Median Barrier
Authors: Rohde John R. , Reid John D. , Sicking Dean L.
Published: April 2007

The design and crash test results of a median barrier version of the Flared Energy-Absorbing Terminal, known as FLEAT-MT, are presented. This energy-absorbing terminal is designed for use with a W-beam, strong-post median barrier. The FLEAT-MT terminal uses two standard FLEAT terminals, one for each of the two W-beam rail elements. The energy-absorbing capability of the FLEAT-MT terminal is based on the sequential kinking concept, similar to that used with the Sequential Kinking Terminal and FLEAT guardrail terminals. Three full-scale vehicle crash tests were conducted to evaluate the impact performance of the FLEAT-MT terminal in accordance with guidelines set forth in NCHRP Report 350: Test 3-35—pickup truck redirection test (Test No. FMT-1), Test 3-31—pickup truck head-on test (Test No. FMT-2), and Test 3-39—pickup truck reverse-direction test (Test No. FMT-3M). The terminal performed as designed. The FLEAT-MT terminal meets all evaluation criteria for a Test Level 3 median barrier terminal set forth in NCHRP Report 350. The FLEAT-MT terminal is being evaluated by FHWA for approval to be used on the National Highway System.
Crash Testing and Analysis of Work-Zone Sign Supports
Authors: Polivka Karla A. , Faller Ronald K. , Rohde John R. , Sicking Dean L.
Published: April 2007

A variety of traffic-controlling devices are used in work zones; some of these are not normally found on the roadside or in the traveled way outside of the work zones. These devices are used to enhance the safety of the work zones by controlling the traffic through these areas. Because of the placement of the traffic control devices, the devices themselves may be potentially hazardous to both workers and errant vehicles. The impact performance of many work-zone traffic control devices is mainly unknown, and to date limited crash testing has been conducted under the criteria of NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The results of full-scale crash testing of flexible panel work-zone sign stands were evaluated and analyzed to quantify the features that successful devices shared, as well as common features of those devices that failed salient safety criteria. Parameters considered included sign base and upright properties, sign height, cross-member properties, and ancillary details. Results pointed to three problematic, fundamental design issues: ( a) combinations of base and upright stiffness and strength that generally lead to significant windshield damage, ( b) cross members that lead to windshield damage in the end-on (90°) impact orientation, and ( c) appurtenances that have an impact on performance. Although there are a significant number of variables that control the performance of a given device, these generalizations offer a basis for the evaluation of the fundamental design elements.
Critical Impact Points for Transitions and Terminals
Authors: Bligh Roger P. , Mak King K.
Published: April 2007

Guidelines for evaluating the safety performance of roadside safety features generally recommend that a worst case or critical impact point (CIP) be selected for crash testing. NCHRP Report 350 presents families of curves that can be used to determine the CIP for a transition section. However, these curves have been observed to overestimate the stiffness of a transition system and provide CIP values closer to the more rigid system of the transition (e.g., bridge rail end) than appropriate. New CIP selection curves for transitions are presented. A procedure is provided to aid in determining the CIP for transition sections with multiple rail elements or variations in post strength and post spacing. Various existing and theoretical transitions systems with wide-ranging combinations of beam and post strengths were used to validate the curves. The newly developed CIP relationships for transitions are recommended in lieu of the existing relationships contained in NCHRP Report 350. To facilitate the development of guidelines for the selection of a CIP for terminals, a new definition is proposed. The proposed definition for the CIP is the point along the terminal at which vehicle behavior transitions from gating to redirection. A methodology for determining the CIP using computer simulation techniques is investigated. The data clearly demonstrate that the selection of a single default impact location for all terminal configurations may not provide the CIP for many designs.
Fatigue Damage in Roller-Compacted Pavement Foundation with Recycled Aggregate and Waste Plastic Strips
Authors: Sobhan Khaled , Mashnad Mehedy
Published: April 2007

Repeated-load tests were conducted in the laboratory on an alternative low-strength roller-compacted concrete material containing cementbound reclaimed crushed aggregate, Class C fly ash, and strip reinforcement made of waste high-density polyethylene plastic. During cyclic loading tests, the dynamic midspan deflection was recorded for all loading cycles to failure for the purpose of characterizing the damage accumulation process in the material. The primary motivation for evaluating this composite (with >90% recycled materials) was to develop an alternative high-quality foundation layer for a conventional flexible or rigid pavement while addressing such an increasingly crucial issue as solid waste disposal in the United States. The main objectives of this endeavor were to evaluate the flexural fatigue behavior of the new composite and to evaluate the accumulation of fatigue damage in the material. Results indicate that the fatigue strength and endurance limit of this material are similar to those of traditional stabilized pavement materials. A nonlinear power law is suggested to describe the relationship between the accumulated permanent deformation and the expended fatigue life. Fatigue damage computed using a dissipated energy approach indicated that damage accumulation in this material approximately follows Miner’s rule for cumulative damage, which is often used in pavement engineering. Results of this study provide insight into the durability characteristics of these emerging new alternative materials.
Alkali-Silica Reactivity Resistance of High-Volume Fly Ash Cementitious Systems
Authors: Shon Chang-Seon , Zollinger Dan G. , Sarkar Shondeep L.
Published: April 2007

The role of high-volume ASTM Class F fly ash (58% by mass of cement) in reducing expansion caused by alkali-silica reaction was investigated. A series of modified ASTM C1260 tests were performed with three different concentrations of NaOH solution and over an extended test period of 28 days; a reactive siliceous fine aggregate was used. Test results confirm that replacing 58% of portland cement (by mass) with high-volume fly ash in a cementitious system significantly helps control expansion caused by alkali-silica reaction.
Using Epifluorescence Optical Microscopy to Identify Causes of Concrete Distress: Case Study
Authors: Sutter Lawrence L. , Peterson Karl R. , Van Dam Thomas J. , Smith Kurt
Published: April 2007

Materials-related distress (MRD) has affected many portland cement concrete pavements. Identifying the specific cause of MRD is not always possible, but with the use of appropriate techniques and a diagnostic approach, the cause can be determined in many cases. In a case studied as part of an FHWA project titled Detection, Analysis, and Treatment of Materials-Related Distress in Concrete Pavements, apparent MRDs were identified. In one case study, determination of the effective water-to-cement ratio (w/c) by epifluorescence microscopy was the key to understanding the cause of distress. The effective w/c, which may not be exact for a given concrete on an absolute basis, was used to compare two concrete microstructures on a relative basis. Stereo-optical microscopy, petrographic optical microscopy, and scanning electron microscopy were also used to identify the MRD diagnostic features present in the distressed concrete. As a result of this analysis, evidence of paste freeze–thaw and deicer attack was identified, but the principal cause of the distress probably was a high w/c in the distressed concrete.
Effect of Curing Methods on Durability of High-Performance Concrete
Authors: Nassif Hani , Suksawang Nakin
Published: April 2007

Many state departments of transportation are currently either using high-performance concrete (HPC) or developing new mix proportions for the application of HPC to transportation structures, with emphasis on bridge decks. However, many state engineers have observed that curing methods and conditions in the field affect the behavior of HPC structures. Moreover, little is known about the effect of curing on the long-term durability of HPC. Therefore, it is necessary to understand the behavior of HPC under various curing conditions and durations and the effect of pozzolanic material such as fly ash and silica fume on rapid chloride permeability (RCP). These factors were studied as part of a project for the New Jersey Department of Transportation to develop and implement mix design and technical specifications for HPC transportation structures such as pavements and bridges. Several mixes were tested, and the best mix was selected on the basis of strength and shrinkage test performance. The long-term durability was assessed by tests for RCP, creep, and freeze–thaw behavior. Moreover, the effect on HPC of four curing methods—moist curing, air-dry curing, burlap wrap, and curing compound—was investigated. Moist-cured cylinders performed better than those cured with other methods, and a minimum of 14 days of cure was required for HPC to attain its full strength.
Test Method for Appraising Future Durability of New Concrete Bridge Decks
Authors: Yaman I.O. , Birgul R. , Aktan H.M. , Hearn N. , Staton J.F.
Published: April 2007

The nondestructive test procedure for quantifying the future durability of bridge deck concrete is based on the fundamental relationship between ultrasonic pulse velocity (UPV) and the permeability of an elastic medium. An experimental study using standard concrete cylindrical specimens (ASTM C192) documented adequate sensitivity between UPV and permeability. The test procedure uses a parameter directly proportional to increase in-field concrete permeability called paste quality loss (PQL). The PQL is computed from UPV measurements on standard concrete specimens made from field concrete mixture (ASTM C31) and measurements on field concrete. Deck replacement projects on three National Highway System bridges were used as demonstration sites to implement the test procedure. The 56-day PQLs were calculated as 15%, 28%, and 9%, demonstrating a significant variability in the permeability of the three bridge decks. Field permeability tests were also conducted with Figg’s apparatus for comparison purposes. The PQL evaluation from postconstruction measurements is an effective and reliable method for testing the future durability of bridge decks.
Transit Path-Choice Models That Use Revealed Preference and Stated Preference Data
Authors: Lam Soi-Hoi , Xie Feng
Published: April 2007

A study was conducted of the trip-making behavior of transit users in a complex transit network with input of travel information in an increasingly complex and information-rich transit environment. A modeling framework to assess the preferences of commuters toward a range of factors and alternatives was produced. Path-choice models on transit services of Singapore were developed using mixed revealed preference (RP) and stated preference (SP) data. RP models were estimated using data obtained in the 1997 Household Interview Survey. An SP survey based on 44 scenarios was conducted, which yielded 307 responses at 12 different locations in Singapore. Models based on pure RP data, pure SP data, and mixed RP and SP data were estimated. For transit users, the decision of which path to take relies on the trade-offs among attributes of journey time and other factors. The significant attributes in the models indicate that the transit path choice is a multi-criteria decision-making process. This suggests that the usual way of transit path assignment in many planning models based on single criterion, such as minimum time, may not be appropriate in choice situations. Path-choice models developed and calibrated provide important fundamental knowledge of the way transit services are to be utilized by travelers, for use in a wide range of applications, such as multimodal transit service planning models, transit demand modeling, and integration of the transit path-choice models in intelligent transportation systems applications.
FTA New Starts: Intermodal Surface Transportation Efficiency Act of 1991 and Transportation Equity Act for the 21st Century Funding Commitments
Authors: Emerson Donald J.
Published: April 2007

By early 2001, the Federal Transit Administration (FTA) had entered into full funding grant agreements for more than 30 New Starts projects since enactment of the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA). Projects funded under ISTEA and its successor, the Transportation Equity Act for the 21st Century, were reviewed, and how the program has changed during the past decade was assessed. The growth in the size of FTA’s “New Starts Pipeline” was examined, and the funded projects were surveyed for their characteristics, geographic distribution, and trends in non–Section 5309 funding. Observations were drawn that may be relevant to reauthorization of the New Starts program in 2003.
International Perspective on the Changing Structure of the Urban Bus Market
Authors: Finn Brendan , Nelson John
Published: April 2007

In urban areas worldwide, fundamental changes are taking place in participation of the public sector in planning, direct provision, and financing of urban bus services. Trends have emerged toward separating roles in transit planning and operation, opening markets to the private sector through direct entry or tendering, and establishing ways for the private sector to innovate in market development. Although in some cases these changes parallel U.S. practices in contracting out services, the international trends often radically alter both the balance of the initiative between the public authority and the operator, and participation in the market. These changes in turn require a fresh look at the functions and organization of a transport authority, so that it can effectively meet these new challenges. First, these trends and the underlying motivations in Europe, the former Soviet Union, Australia, and developing countries were reviewed. Second, competitive tendering in procuring urban bus services in a diverse set of selected locations was examined, taking into account the differences in both purpose and practice. Third, what the authority is trying to achieve and the functions it needs to assure were considered, along with the sustainability of the competitive tendering process. Unlike the typical U.S. experience in which the structure remains essentially unchanged, the Eurasian and Southern Hemisphere experiences typically involve fundamental changes to the system that have substantial transition costs and are not easily reversed. If either the process or the benefits are not sustainable, the implications are severe. Tender prices on re-bid, labor and human issues, and network design are suggested as key issues.
Estimating Passenger Miles, Origin–Destination Patterns, and Loads with Location-Stamped Farebox Data
Authors: Navick David S. , Furth Peter G.
Published: April 2007

Integrating an electronic farebox with a location system can provide location-stamped records of passenger boardings, a valuable source of information on passenger travel patterns. However, this information is of small value unless the pattern of passenger alightings can also be determined, since most relevant measures of interest—passenger loads, passenger miles, and origin–destination (O-D) patterns—require a knowledge or at least estimate of passenger alightings by stop. The assumption of symmetry—that the pattern of passenger alightings in one direction mirrors the daily boardings pattern in the opposite direction—is explored. Estimation methods using this assumption are tested at the trip, route, and system levels using a full-day’s set of on–off counts on five Los Angeles area routes. Tests at the route level indicate that although perfect symmetry does not exist, patterns are substantially similar on many routes. Based on the Los Angeles data, it can be found that systemwide estimates of passenger miles made using this method satisfy U.S. National Transit Database precision requirements; however, this finding should be confirmed using data from other cities. Proposed and tested, with a small amount of success, is a method for estimating trip-level O-D patterns using location-stamped farebox data based on the symmetry principle and a gravity model. Location-stamped farebox data can also be used to estimate passenger loads in real time to support control measures such as conditional priority at traffic signals without requiring automatic passenger counters.
Intertechnology Effects in Intelligent Transportation Systems
Authors: Kanchi Seshasai , Levinson David M. , Gillen David
Published: April 2007

The expected benefits of varying combinations of intelligent transportation system applications, such as freeway service patrol, changeable message signs, and ramp metering, were examined. The research analyzed the simulated results of a stylized network in a microscopic traffic simulator. The traffic network included parallel roadways, ramp meters, and changeable message signs. These technologies were tested in various combinations. The effectivenesses were determined, and a measure of inter-technology economies was defined. In brief, additional technologies were found to be subadditive, and more benefits came from each technology in isolation than from the bundling of each with other technologies.
Genetic Algorithm-Based Optimization Approach and Generic Tool for Calibrating Traffic Microscopic Simulation Parameters
Authors: Ma Tao , Abdulhai Baher
Published: April 2007

GENOSIM is a generic traffic microsimulation parameter optimization tool that uses genetic algorithms and was implemented in the Port Area network in downtown Toronto, Canada. GENOSIM was developed as a pilot software as part of the pursuit of a fast, systematic, and robust calibration process. It employs the state of the art in combinatorial parametric optimization to automate the tedious task of hand calibrating traffic microsimulation models. The employed global search technique, genetic algorithms, can be integrated with any dynamic traffic microscopic simulation tool. In this research, Paramics, the microscopic traffic simulation platform currently adopted at the University of Toronto Intelligent Transportation Systems Centre, was used. Paramics consists of high-performance, cross-linked traffic models that have multiple user adjustable parameters. Genetic algorithms in GENOSIM manipulate the values of those control parameters and search for an optimal set of values that minimize the discrepancy between simulation output and real field data. Results obtained by replicating observed vehicle counts are promising.
Parking Search Time and Information Identification for Off-Street Spaces in New York City
Authors: Teng Hualiang (Harry) , Qi Yi (Grace) , Yi Ping
Published: April 2007

A parking information system consisting of a parking information website and roadside displays has been proposed for New York City to alleviate parking difficulties. To justify the implementation of such a system, it is necessary to investigate parking search time and its relationship with parking information. In addition, the parking information items needed for the website and roadside displays and the target markets for this information must be identified. In the investigation, a survey was conducted to collect data on parkers’ demographic and trip characteristics. On the basis of the collected data, the effect of parking information on parking search time was studied, and an ordered probit model was developed. To identify parking information needs, the analysis of variance method was employed to determine the rank of the information items for the website and roadside displays. The profiles of the parkers were also identified for each information item using developed models. The results of the investigation indicated that parking search time is significantly influenced by the amount of parking information parkers possess before starting their trips. Six information items were identified to be the most necessary for the parking information website, and five as most necessary for the parking roadside display. All these information items should be considered when designing a parking information system.
Transmitted Bandwidth and Bit Error Probability of the Safety Warning System
Authors: Geisheimer Jonathan L. , Greneker Eugene F.
Published: April 2007

The safety warning system (SWS) is an inexpensive, low-power, point-to-point communications link designed for intelligent transportation systems’ in-vehicle signing applications at 24.1 GHz. The transmitted bandwidth of the SWS signal was analyzed, and the theoretical results were compared with measured data. The SWS meets Federal Communications Commission bandwidth requirements under all operational conditions. Additionally, because the system typically operates in a cluttered roadway environment, an upper bounds on the bit error probability is modeled under non-line–of-sight conditions. The SWS uses a continuous-phase binary modulation technique. The bit error probability is derived using a maximum likelihood receiver receiving a Rayleigh-distributed signal under additive white Gaussian noise conditions.
Functional Requirements for In-Vehicle Dilemma Zone Warning System at Signalized Intersections
Authors: Moon Young-Jun
Published: April 2007

Functional requirements and an operational algorithm to establish in-vehicle dilemma zone warning systems (DZWSs) at signalized intersections are provided as a part of the driver advisory and collision warning system in the automated vehicle and highway system. The DZWS project, one of Korea’s national intelligent transportation system projects in 2000, is developing an in-vehicle warning device to support drivers’ decision making on whether to stop or to proceed to clear the intersection before the onset of a yellow signal to avoid the high risk of a collision at signalized intersections. The dilemma zone concept, resulting from research and methodology pioneered in traffic engineering on drivers’ decisions, has been used to design the yellow warning interval. The operational and functional concepts of the DZWS are explored for appropriate approach speeds and deceleration rates at two signalized intersection sites. Findings from this research suggest that the algorithm should be implemented in developing and testing in-vehicle DZWS at two signalized intersection sites to improve driver compliance with stopping at the onset of yellow.
Effects of Adaptive Cruise Control Systems on Highway Traffic Flow Capacity
Authors: Vander Werf Joel , Shladover Steven E. , Miller Mark A. , Kourjanskaia Natalia
Published: April 2007

The effects on traffic flow of increasing proportions of both autonomous and cooperative adaptive cruise control (ACC) vehicles relative to manually driven vehicles were studied. Such effects are difficult to estimate from field tests on highways because of the low market penetration of ACC systems. The research approach used Monte Carlo simulations based on detailed models presented in the literature to estimate the quantitative effects of varying the proportions of vehicle control types on lane capacity. The results of this study can help to provide realistic estimates of the effects of the introduction of ACC to the vehicle fleet. Transportation system managers can recognize that the autonomous ACC systems now entering the market are unlikely to have significant positive or negative effects on traffic flow. An additional value of studying ACC systems in this way is that these scenarios can represent the first steps in a deployment sequence that will lead to an automated highway system. Benefits gained at the early stages in this sequence, particularly through the introduction of cooperative ACC with priority access to designated (although not necessarily dedicated) lanes, can help support further investment in and development of automated highway systems.
Infrastructure Collision-Avoidance Concept for Straight-Crossing-Path Crashes at Signalized Intersections
Authors: Ferlis Robert A.
Published: April 2007

Concepts to improve intersection safety with infrastructure-only and infrastructure-vehicle-cooperative collision-avoidance systems were assessed. These systems address straight-crossing-path crashes at signalized intersections. System components include sensors, processors, driver information devices, roadside-to-vehicle communication systems, and on-vehicle systems. The deployment model to realize infrastructure vehicle cooperation assumes the introduction of infrastructure-only systems that service all drivers with warnings provided by roadside information devices. These systems would be followed by the addition of roadside-to-vehicle communication systems that service drivers of intelligent vehicles through in-vehicle warnings. These concepts can be used to avoid a crash when a vehicle violates the signal. Equations of motion illustrate how a simple algorithm can be used to identify potential violators by using speed at a measurement point on the approach to an intersection. The example suggests that most potential signal violators can be warned in time to stop before they collide with a vehicle from the cross street. Analysis also indicates that when warnings of the possible signal violation are conveyed to drivers on the cross street, many of these drivers can also stop before colliding with the signal violator. In the example, 88% of the relevant straight-crossing-path crashes were addressed by providing timely warnings to either the violators or the other drivers. Deployment costs and benefits were estimated to demonstrate the potential value of infrastructure intersection collision-avoidance systems.
Inexpensive, Infrastructure-Based, Intersection Collision-Avoidance System to Prevent Left-Turn Crashes with Opposite-Direction Traffic
Authors: White Bryon , Eccles Kimberly A.
Published: April 2007

An infrastructure-based intersection collision-avoidance system (ICAS) designed to provide guidance for left-turning vehicles that have secondary right-of-way and are attempting a turn across the path of opposite-direction traffic is proposed. These types of crashes are most prevalent where a left turn is made from a major road approach. A dominant causal factor in this type of crash is the inability of the left-turning motorist to adequately perceive the required gap for a safe left turn. The proposed ICAS compares the presumed arrival time of the opposite-direction vehicle with the presumed time for a motorist to turn left. Based on this comparison, the system provides guidance to the left-turning motorist in the form of a dynamic sign placed in the same line of sight of opposite-direction traffic, so that motorists will have a “second opinion” to aid in their left-turn decisions. The system is composed of four modules: ( a) a left-turn assistance device, ( b) left-turn presence detection, ( c) opposite-direction detection, and ( d) a system processor. The system differentiates between left-turning passenger cars and left-turning heavy vehicles and tailors its guidance appropriately. A non-hardware-specific example of the proposed system at a hypothetical intersection was assessed, along with functional requirements and system limitations.
Fluorescent Sign Colors for Incident Management Trailblazing: Evaluation of Assignments in Manual on Uniform Traffic Control Devices
Authors: Neale Vicki L. , Brich Stephen C. , Anders Richard L.
Published: April 2007

Previous research evaluated the use of unassigned sign colors from the Manual on Uniform Traffic Control Devices for incident management trailblazing; however, fluorescent sign colors were not evaluated. Since evidence suggests that fluorescence on signs improves conspicuity, the following colors were evaluated along a contrived test route with an instrumented vehicle: black on fluorescent coral, fluorescent yellow on fluorescent purple, black on fluorescent yellow-green, and yellow on purple in nonfluorescent colors. No significant differences in driving performance were exhibited among the four experimental sign-color combinations. Based on questionnaire results, the black on fluorescent yellow-green sign was preferred by younger and older drivers during both day and night visibility conditions. However, fluorescent yellow-green was subsequently assigned by the Federal Highway Administration for pedestrian, school, and bicycle crossings. For the remaining colors, black on fluorescent coral was ranked highest for visibility and overall preference, followed by fluorescent yellow on fluorescent purple, with nonfluorescent yellow on purple least preferred. Black on fluorescent coral was preferred over fluorescent yellow on fluorescent purple during daytime viewing conditions, while the reverse was true for nighttime. Drivers also commented that the arrow on the sign was too small to determine directional information from a comfortable distance.
Driver Understanding of Simultaneous Traffic Signal Indications in Protected Left Turns
Authors: Noyce David A. , Kacir Kent C.
Published: April 2007

A comprehensive assessment of protected and permitted left-turn (PPLT) signal displays was performed considering safety, operational performance, and driver-understanding measures. The research focused on a study of driver understanding of protected left-turn indications. All currently used PPLT display arrangements and protected indication combinations were evaluated, including those with simultaneous green-arrow and red- or green-ball indications and those with the green-arrow indication only. Driver understanding was evaluated through a computer-based driver survey completed by 2,465 drivers. In total, 73,950 survey responses were received pertaining to the 200 different survey scenarios evaluated, 24,863 pertaining to protected left-turn indications. Findings show that the simultaneous illumination of the green-arrow and red-ball indications in a five-section PPLT signal display during a protected left-turn phase significantly reduces driver understanding and increases driver error. This finding is especially true for drivers over the age of 65. Simultaneous illumination of the green-arrow and green-ball indications also resulted in levels of driver understanding lower than the green-arrow-only indication; however, these differences were not statistically significant.
Roundabout Warrants: Proposed Framework for Future Development
Authors: Chapman Jeremy R. , Benekohal Rahim F.
Published: April 2007

The available research in the area of roundabout intersections was surveyed with focus primarily on concerns about their installation. The Federal Highway Administration’s 2000 publication, Roundabouts: An Informational Guide, examines what should be done after the decision has been made to install a roundabout. This guide, while a good reference, does not provide specific decision-making criteria, the main focus of this proposed framework. The areas of focus are not to be considered exhaustive or complete but as suggested criteria, as the use of warrants seeks to imply. The areas covered in depth by these criteria are pedestrian volume, horizontal alignment, vertical alignment, and unbalanced flow volumes. In addition, safety and relevant local concerns should be focused on in the overall decision-making process.
Photo Enforcement at Highway–Rail Grade Crossings in the United States: July 2000–July 2001
Authors: Carroll Anya A. , Warren Judith D.
Published: April 2007

Nearly 50% of U.S. highway–rail crossing accidents occur at public crossings equipped with automated warning devices, of which 78% are passive and 22% have active warning systems. This is a disproportionate amount of accidents occurring at active sites. The use of photo enforcement at public highway–rail grade crossings became a focal point for study. This technology observes and records driver and pedestrian behavior, as driver behavior is at the root of the crossing safety problem. Judicial concerns and public perception and support levels are also issues of concern. Photo enforcement is an option to assist law enforcement to increase safety at public crossings. While some privacy issues remain, this system can be a reliable, cost-effective way to discourage unsafe driver behavior. Today, 75 countries use traffic cameras. Internationally, photo enforcement has been in use for more than 20 years. Experience has shown that visible, high-profile law-enforcement programs like photo enforcement reduce the number of highway–rail crossing violations. Photo enforcement at six highway–rail crossings across the United States showed positive results in reducing violations. The results of investigations at the six sites indicated a reduction of violations in the range of 34% to 92%. Implementing the technology to detect a violator is one aspect of reducing violations; persuading police and civil officials to adapt enforcement programs is another.
Assessment and Improvement of Safety at Finnish Railway–Road Grade Crossings
Authors: Kallberg Veli-Pekka , Anila Matti , Pajunen Kirsi , Kallio Mikko , Hytönen Jouni
Published: April 2007

A method for determining whether the safety of a railway–road grade crossing is reasonable was assessed by examining the results of its application to 360 Finnish grade crossings. Safety was considered reasonable if the conditions at the grade crossing were such that road users have available all the information necessary for safe crossing. At passive grade crossings, this condition is usually met when a road vehicle can cross the railway in less time than it takes for a train to arrive at the crossing from the farthest point at which the road user can see it. In the application of the method, crossing times for a car, a truck, and a trailer truck were calculated with an advanced vehicle-movement simulation model, taking into account the gradient of the road. These times were frequently too short. In such cases, measures for quick implementation were suggested. Most frequently these measures concerned clearing of sight-restricting vegetation, improving the vertical profile of the road, banning long vehicles from using the grade crossing, and reducing the speed limit of trains. Vehicle type-specific bans and reduced speed limits can usually be removed later if the crossing is equipped with barriers.
Computational Vision Model to Assess Work-Zone Conspicuity
Authors: Barton Jay E. , Misener James A. , Cohn Theodore E.
Published: April 2007

A computational means to assess the conspicuity of highway features was developed, verified, and then applied to a sample construction work zone scene. This work was conceived as a balance between modeling the complex phenomena within the human visual system and the need for a simple applications-oriented tool for practitioners to derive a quantitative relative assessment of real-world construction work zones to rank choices in terms of conspicuity. The results indicate that the vision model–based tool can assess the relative conspicuity of individual elements of a roadway or roadside scene and is relatively straightforward in use. As such, it holds potential value in virtual prototyping of work-zone sight lines, colors, and placement of hazard warning cues, such as cones, markings, and reflective vests.
Multimodal Corridor Level-of-Service Analysis
Authors: Dowling Richard G. , McLeod Douglas , Guttenplan Martin , Zegeer John D.
Published: April 2007

The 2000 release of the Highway Capacity Manual (HCM) provides for the first time a corridor analysis method that guides users in the application of various chapters of the HCM to the analysis of automobiles and transit in a corridor. Together with the recent publication of the Transit Capacity and Quality of Service Manual (TCQSM), the HCM 2000 represents a significant advance in the direction of multimodal level-of-service (LOS) analysis. However, relatively little guidance is given in either the HCM or the TCQSM on the compilation of automobile and transit segment levels of service into a measure of corridor level of service. In addition, bicycles and pedestrians are ignored in the corridor methodology. A methodology was developed and tested in Florida for measuring and reporting the user-perceived quality of service for highway corridors from a multimodal perspective. Automobile and transit LOS analyses are based on the HCM 2000 and TCQSM, respectively. Bicycle and pedestrian levels of service are based on the bicycle and pedestrian LOS models, respectively. Four classes of corridors are recommended, and the methodology was tested on two classes of urban corridors, with and without a freeway. The methodology is applied in three steps: ( a) corridor definition, ( b) computation of modal level of service, and ( c) reporting of results. The methodology was applied to six case studies throughout Florida at generalized and conceptual planning levels. Conclusions about the methodology were drawn from the case studies; the main conclusion is that the methodology provided a reliable overall indicator of corridor level of service by mode.