Transportation Intelligence

Volume 5 Number 4

August 2007

Structures

Environment

Safety

Administration

Traffic Operations

Pavements

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Structures
Challenges for use of fixed fire suppression systems in road tunnel fire protection
Fixed fire suppression systems are used as an effective fire protection measure in many areas of the built environment. However, many countries have not considered them necessary or even acceptable for tunnel protection. There are concerns on the use of these systems in tunnel environments, such as the visibility reduction during evacuation caused by water discharge, the associated high cost for installation and maintenance, their performance in suppressing shielded fires, potential hazards presented by hot steam and deflagration generated in suppressing large flammable fuel fires, as well as limited knowledge on the most suitable suppression systems for tunnel protection. However, with a significant increase in the number and the scale of fire accidents in tunnels around the world over the last ten years there is renewed interest in the use of fixed fire suppression systems for tunnel protection. (National Research Council of Canada Institute for Research in Construction report NRCC-49232, March 2007, 10 p.)

Pavements
Guide technique sur la mise en place des enrobés bitumineux - version préliminaire (Technical guide on the laying of asphalt binders - preliminary version)
This guide, produced by the Direction du laboratoire des chaussées of the Ministry of Transportation of Quebec, describes good practices in laying binders. The document is above all a tool and quick reference allowing supervisors to pay special attention to the various aspects affecting the quality and durability of binders. More specifically, this guide discusses in a non-exhaustive manner the trade practices to be followed from the binder plant post-manufacture to final compacting on the construction site. (Quebec Ministère des Transports, 2007, 64 p.)

Rapid Pavement Construction Tools, Materials, and Methods
To address the need to deliver cost-effective projects while minimizing traffic impacts, the Washington State Department of Transportation (WSDOT) desires to improve their knowledge, awareness and retention of rapid pavement construction tools, materials and methods. This project discusses the implementation, use and experience of using the following items related to rapid pavement construction: CA4PRS (Construction Alternatives for Pavement Rehabilitation Strategies), portland cement concrete (PCC) pavement panel replacement, polymer concrete and traffic closure windows. CA4PRS is a Microsoft Access-based software program for predicting construction productivity for highway rehabilitation/reconstruction. It was tested in two case studies and has proved capable of providing meaningful scheduling and productivity inputs into early project planning. Panel replacement techniques and polymer concrete construction are reviewed (including contractor interviews) in an effort to document past successes and failures as well as key decision points when making future project decisions. Finally, a review of traffic closure windows for rapid construction is presented. (Washington State Department of Transportation Report WA-RD 670.1, May 2007, 311 p.)

Structures

Integral Abutment Bridge with Precast Concrete Piles
This report presents the details of the first integral abutment bridge in the state of Iowa that utilized precast, prestressed concrete piles in the abutment. The bridge, which was constructed in Tama County in 2000, consists of a 110 ft. long, 30 ft. wide, single-span PC girder superstructure with a left-side-ahead 20º skew angle. (Iowa State University Center for Transportation Research and Education report IHRB Project TR-438, May 2007, 74 p.)

Comportement au feu des tunnels routiers (Fire behaviour of road tunnels)
Every new tunnel on the national road system of France must be designed in accordance with the conditions specified in the technical instruction appended to circular 2006-63, which includes provisions on the fire behaviour of road tunnels and related structures. At the request of the Comité d'évaluation de la sécurité des tunnels routiers, the Centre d'études des tunnels (CETU) formed a task force to produce a guide on the fire behaviour of road tunnels to help contractors and managers implement these provisions. (France - Direction des routes - centre d'Études des tunnels - guide, 2005, 58 p.)

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Environment

Development and Evaluation of Devices Designed to Minimize Deer-Vehicle Collisions
This study was designed to: 1) provide a comprehensive literature review of all pertinent aspects related to deer-vehicle collisions, 2) evaluate the effectiveness of Strieter-Lite wildlife warning reflectors for altering the behavior of white-tailed deer along roadways, 3) generate basic information on the visual capabilities of white-tailed deer, 4) determine the hearing range of white-tailed deer, 5) improve on existing technologies or develop new strategies for reducing the incidence of deer-vehicle collisions. This final report is a compilation of the literature review, the Ph.D. dissertation of Gino D’Angelo (D’Angelo 2007), and the Master of Science Thesis of Sharon Valitzski (Valitzski 2007). (Georgia Department of Transportation Report, July 2007, 261 p.)

Synthesis of Noise Effects on Wildlife Populations
This report contains a summary of ongoing work on the effects of noise on wildlife populations. There is a paucity of information on the response of invertebrates to noise, particularly the levels likely to be encountered along roads. Significant populations of some species are found along rights-of-way, although others such as aquatic forms may be adversely affected whether by the road itself or by noise is unclear. Existing information (although incomplete) would suggest that fish are unlikely to be adversely affected by noise levels from road. Reptiles and amphibians show some barrier effect due to roads, but there is no clear evidence of a noise effect alone. Recent work has suggested that behavior in burrowing toads may be affected by noise and this will require further study. Birds have received the most study and in some cases are negatively affected both in numbers and in breeding by the proximity to roads. In other cases the effect is the opposite and there are reports of many species using roadside habitat in some areas. Large mammals may be repelled by noise, although in most cases the effect appears to be slight to moderate. Small mammals do not appear to be adversely affected by road noise occurring in significant numbers in rights-of-way. There appears to be a physical barrier effect of roads for many mammals. Recommendations for future study are included. (US Federal Highway Administration Report FHWA-HEP-06-016, September 2004, 67 p.)

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Safety

Safety Assessment of Interchange Spacing on Urban Freeways
The decision to build a new interchange between an existing pair of interchanges is made by evaluating whether there is sufficient need for traffic to enter and/or exit the freeway at that location. The obvious intent is to reduce the systemwide travel times and delays for all users by providing convenient freeway access and egress. Although there are ways to evaluate these operational benefits quantitatively, to date researchers have not expressed in measurable terms the compromise in safety, or the increase in crashes per mile of freeway. This knowledge is essential for conducting a comprehensive cost-benefit analysis of new interchange construction projects. To fill this void, we endeavored to study interchange spacing from a safety perspective by estimating regression models to express crash frequencies as a function of highway characteristics, including interchange spacing. We then used the regression models to quantify the crash sensitivity to interchange spacing for fatal and injury crashes. We used data pertaining to freeway sections from 7 urban freeways in California and 10 urban areas in Washington for building the regression models. (US Federal Highway Administration Techbrief FHWA-HRT-07-031, 2007, 12 p.)

Putting the Brakes on Crossover Crashes: Median Barrier Research and Practice in the U.S.
From 2001 to 2003, more than 600 cross-median crashes occurred on Wisconsin highways. Personal injury or fatality was involved in six out of 10 cases. Reducing these crashes is a key component of the 2006-2008 Wisconsin Strategic Highway Safety Plan, with the goal to cut cross-median fatal and severe injury crashes 10 percent by 2008. There are three focus areas—collection of data and refinement of ongoing median crossover investigation, refinement of WisDOT’s run-off-the-road assessment tool to analyze two-lane road head-on crashes, and development and implementation of potential solution strategies. The Bureau of Project Development asked us to locate median barrier procedures used by other state DOTs, with an emphasis on identifying guidelines used for deciding where to install median barriers and which types to use, and criteria used for acceptance/rejection of temporary concrete barriers. (Wisconsin Department of Transportation Report, March 2007, 67 p.)

Audible Signals for Pedestrian Safety in LRT Environments
This digest provides guidelines for the application of audible signals for pedestrian safety in light rail transit (LRT) environments. The guidelines include descriptions of audible signal systems and associated operating procedures., their integration with other crossing measures, criteria for their use, and their effectiveness and limitations. The guidelines are organized by location of audible warning devices and alignment type. (TRB’s TCRP Research Results Digest 84, May 2007, 22 p.)

Measuring (un)safety of roads
It is difficult to measure the safety of roads. Various ratios are used: the number of crashes per road, per kilometre road, and per motor vehicle kilometre travelled. The ratios can be used to compare roads with each other. To give meaning to the value of a road safety ratio, reference values are necessary. This Fact sheet describes how these reference values are determined and presents various ways of visualising the risk of roads. (SWOV Institute for Road Safety Research Fact Sheet, April 2007, 5 p.)

Recognizable road design
One of the principles of Sustainable Safety is that a road should have a recognizable design and a predictable alignment. If this is the case, road users know which behaviour is expected of them and what they can expect from others. This would cause more predictable behaviour, which contributes to the prevention of crashes. What do we mean exactly by recognizability of roads and what is a recognizable road design? This fact sheet will give the theoretical background of the concept of recognizability, and describe how to apply this in practice. The Essential Recognizability Characteristics guideline will be discussed and the most important results of our research into road recognizability will be presented. (SWOV Institute for Road Safety Research Fact Sheet, May 2007, 6 p.)

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Administration

Current Cost-Benefit Evaluation of Short-Term Warranties for Hot-Mix Asphalt Pavements
The purpose of this report is to provide the reader with the current cost-benefit evaluation of hot mix asphalt (HMA) projects constructed using the 3 and 5-year warranty specifications developed by Colorado Department of Transportation (CDOT). There were eight projects evaluated using the 3-year warranty specifications and two projects evaluated using the 5-year warranty specifications. Each warranty project was evaluated with a comparable non-warranty (control) project. Overall, 214.6 lane-miles of warranty projects were constructed and compared to 276.6 lane-miles of control projects. (Colorado Department of Transportation Report CDOT-2007-10, June 2007, 107 p.)

Statewide Economic Benefits of Transportation Investment
This study evaluates the statewide economic benefits of future transportation investment in Colorado using available data and benefits studies conducted in other states. Objectives of this study are to provide Colorado stakeholders results consistent with their guidance in the CDOT Economic Benefits of Transportation Research Scoping Study (May 2006) and to identify data needs and other information necessary to perform a future in-depth analysis of benefits by region within the state. This research focuses on the benefits of additional transportation spending above a baseline investment scenario. (Colorado Department of Transportation Report CDOT-2007-5, April 2007, 68 p.).

Maintaining Traffic Sign Retroreflectivity: Impacts on State and Local Agencies
This report analyzes the impacts that might be expected from the adoption of proposed minimum maintained retroreflectivity levels for traffic signs to improve night visibility. The report evaluates the broad spectrum of concerns expressed by State and local agency staff at four workshops held during the summer of 2002. These include administrative, fiscal, implementation, and tort liability concerns. The report includes a summary of previous studies, including those of several State agencies, to determine the impacts of the proposed new minimum maintained levels for traffic sign retroreflectivity. (US Federal Highway Administration Report FHWA-HRT-07-042, April 2007, 38 p.)

Strategies Are Available for Making Existing Road Infrastructure Perform Better
For the past several decades, the capacity of the nation's road network has not grown fast enough to keep pace with demand. The increasing congestion is apparent to millions of commuters and freight operators. Although road building is perhaps the most familiar antidote, Congress, the Department of Transportation (DOT), and transportation research have emphasized the need to more efficiently use the existing infrastructure as a means to control congestion. GAO was asked to examine various issues associated with increasing the efficient use of existing infrastructure. This report examines the following questions: (1) What factors inhibit the efficient use of the existing infrastructure of roads and highways? (2) What techniques have been developed for making the current infrastructure more efficient and what is known about the results? (3) How have local decision makers implemented these techniques? (4) What strategies exist for increasing the use of such techniques? To address these questions, GAO reviewed existing studies, examined efforts in five states, and sought transportation officials' views, among other things. (US Government Accountability Office Report GAO-07-920, July 2007, 56 p.)

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Traffic Operations

Design, Operation, and Safety of At-Grade Crossings of Exclusive Busways
Exclusive busways in separate rights-of-way may have at-grade crossings with roadways or pedestrian and bicycle facilities. This report provides guidelines for the safe design and operation of at-grade crossings of exclusive busways. The guidelines are based on a detailed literature review, interviews with selected transit agencies, and site visits to Cleveland, Los Angeles, Miami, Orlando, and Richmond (British Columbia). The guidelines are intended to assist transit, traffic engineering, and highway design agencies in planning, designing, and operating various kinds of busways through roadway intersections. This report includes guidance for at-grade intersections along (1) busways within arterial street medians; (2) physically separated, side-aligned busways; (3) busways on separate rights-of-way; and (4) bus-only ramps. The intersections discussed include highway intersections, midblock pedestrian crossings, and bicycle crossings. The resulting guidance provides information that can be applied to enhance safety at busway crossings while maintaining efficient transit and highway operations, and minimizing pedestrian delay.TCRP Web-Only Document 36, available on the TRB website (http://www.trb.org/news/blurb_detail.asp?id=7720), contains Appendixes A through I of the contractor’s final report. (TRB's Transit Cooperative Research Program (TCRP) Report 117, 2007, 51 p.)

Improved Transition Preemption Strategy for Signalized Intersections near At-Grade Railway Grade Crossing
Because the prime objective of the current preemption methods for traffic signals located near highway-railroad grade crossings is to clear vehicles from the crossing, secondary objectives such as maximizing pedestrian safety and minimizing vehicle delay are given less consideration and are often ignored completely. Consequently, the state-of-the-practice traffic signal preemption strategies may result in pedestrian safety and efficiency problems at signalized intersections near highway-railroad grade crossings (IHRGCs). In this paper, an improved transition preemption strategy (ITPS) that is specifically designed to improve intersection performance while maintaining or improving the current level of safety is developed. (Journal of Transportation Engineering, August 2007, pp. 443-454.) (To obtain this article, please contact the TIS.)

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Pavements

Thin Whitetopping - the Colorado Experience
Thin Whitetopping (TWT) is a relatively thin concrete overlay that is bonded to the underlying AC pavement. In Colorado, TWT was developed and is used as a low-maintenance, long-life alternative to an AC overlay for more heavily trafficked roadways. Since June 1990, CDOT has constructed numerous test sections and conducted studies to develop and refine guidelines for constructing TWT. The CDOT guidelines for TWT include lessons learned from extensive field trials, as well as research findings. Economic analysis conducted by CDOT showed that TWT is competitive on project cost alone. With proper planning, TWT can be constructed with minimal disruption to traffic. TWT has been a very successful innovation for CDOT, and Colorado continues to use TWT on a competitive basis for rehabilitation of distressed asphalt pavements. (US Federal Highway Administration TechBrief, 2007, 8 p.)

Axle Load Distribution for Mechanistic-Empirical Pavement Design
Mechanistic–empirical (ME) pavement design often demands default or assumed axle load spectrum data. Using single and tandem axles of the Vehicle Class 9 as examples, this study analyzed the spatial and temporal variations of the load distributions from the long-term pavement performance program traffic database. (Journal of Transportation Engineering, August 2007, pp. 469-479) (To obtain this article, please contact the TIS.)

Effective Shoulder Design and Maintenance
Granular shoulders are an important element of the transportation system and are constantly subjected to performance problems due to wind- and water-induced erosion, rutting, edge drop-off, and slope irregularities. Such problems can directly affect drivers’ safety and often require regular maintenance. The present research study was undertaken to investigate the factors contributing to these performance problems and to propose new ideas to design and maintain granular shoulders while keeping ownership costs low. (Iowa State University Center for Transportation Research and Education Report, June 2007, 296 p.)

Evaluation of Drainable Bases Under Asphalt Pavement
Providing adequate drainage to a pavement system is an important consideration to prevent premature failures due to water related problems, such as pumping action, loss of support, and rutting. Ohio Department of Transportation has adopted several types of materials specifications for permeable bases: (a) ODOT 307 base, including IA, NJ, and CE types, (b) ODOT 306 Cement Treated Base, (c) ODOT 308 Asphalt Treated Base. This research is aimed at investigating the effectiveness of these drainable base materials under asphalt pavements. Both laboratory tests and in-situ monitoring has been carried out. Specific conclusions are as follows: (I) There was no evidence of developing full saturation in the cohesive subgrade soils; (II) The order of drainage efficiency can be established into three categories: (a) ODOT 306 Cement Treated base (25,345 ft/day) and ODOT 308 Asphalt Treated base (25,061 ft/day), (b) ODOT 307 NJ base (3,830 ft/day), ODOT 307 CE (3,705 ft/day), and ODOT 307 IA base (2,280 ft/day), and (c) ODOT 304 medium gradation (1,417 ft/day); (III) The cement treated base materials exhibit the highest resilient modulus values, even after 15 cycles of freeze/thaw conditioning; (IV) The asphalt-treated base materials exhibit relatively higher resilient modulus values than the unbound base materials; (V) The resilient modulus of the unbound base materials, particularly ODOT 304 fine gradation, is sensitive to the percentage of fine content and saturation; (VI) The resistance to permanent deformation of ODOT specific drainable base materials can be ranked from high to low as follows: Cement-treated base, ODOT 307 CE, ODOT 307 IA, ODOT 304, ODOT 307 NJ, ODOT 308 (asphalt treated base) at 77 degree F, and ODOT 308 at 104 degree F. (Ohio Department of Transportation Report FHWA/OH-2007/10, May 2007, 603 p.)

Geosynthetic Materials in Reflective Crack Prevention
Reflective cracking due to shrinkage and brittleness in asphalt pavements can seriously degrade an asphalt overlay before it is near the end of its design life. Geosynthetics have been used to impede the reflection of existing transverse cracking to the new overlay. The geosynthetics are intended to minimize the tension transferred to the overlay from the existing pavement. The Oregon Department of Transportation (ODOT) installed a test section consisting of 98 transverse cracks treated with five different geosynthetic types, 22 transverse cracks treated with crack filling only and a control section of 20 untreated transverse cracks. (Oregon Department of Transportation Report OR-RD-08-01, July 2007, 40 p.)

Evaluating Air-Entraining Admixtures for Highway Concrete
This report explores a procedure for evaluating air-entraining admixtures used in highway concrete. The procedure involves the testing of non-air-entrained concrete and concrete containing the air-entraining admixture under simulated field conditions. The appendixes to the report have been published as NCHRP Web-Only Document 101: Procedures for Evaluating Air-Entraining Admixtures for Highway Concrete (see http://trb.org/news/blurb_detail.asp?id=7888). (TRB's National Cooperative Highway Research Program (NCHRP) Report 578, 2007, 60 p.)

Evaluation of Long-Term Field Performance of Cold In-Place Recycled Roads: Field Distress Survey
Cold in-place recycling (CIR) has become an attractive method for rehabilitating asphalt roads that have good subgrade support and are suffering distress related to non-structural aging and cracking of the pavement layer. Although CIR is widely used, its use could be expanded if its performance were more predictable. Transportation officials have observed roads that were recycled under similar circumstances perform very differently for no clear reason. Moreover, a rational mix design has not yet been developed, design assumptions regarding the structural support of the CIR layer remain empirical and conservative, and there is no clear understanding of the cause-effect relationships between the choices made during the design/construction process and the resulting performance. The objective of this project is to investigate these relationships, especially concerning the age of the recycled pavement, cumulative traffic volume, support conditions, aged engineering properties of the CIR materials, and road performance. (Iowa State University Center for Transportation Research and Education Report IHRB Project TR-502, May 2007, 112 p.)

Pavement Design Using Unsaturated Soil Technology
Pavements are constructed on compacted soils that are typically unsaturated. The negative pore-water pressure (soil suction) due to the ingress of water in between soil particles has a significant effect on pavement foundation stiffness and strength. The study characterized the effects of soil suction on shear strength and resilient modulus of four soils representing different regions of Minnesota. (Minnesota Department of Transportation Report MN/RC-2007-11, May 2007, 246 p.)

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