Transportation Research Record: Journal of the Transportation Research Board

Guidelines for the installation of median barriers presented in the AASHTO Roadside Design Guide have remained essentially unchanged for more than 30 years. In recent years, the need for improved guidance has prompted several states to reevaluate their guidelines and has also precipitated a nationwide research project administered by the Transportation Research Board. The objective of the study, on which this paper is based, was to develop improved guidelines for the use of median barriers on new and existing high-speed, multilane, divided highways in Texas. The purpose here is to present some modeling and benefit–cost analysis results from that study, with a focus on the results from a particular data set developed under a cross-sectional with–without study design. The highways of interest are those classified as Interstates, freeways, and expressways with four or more lanes and posted speed limits of 55 mph (88 km/h) or higher. The models employed to estimate median-related crash frequencies and severities, including the Poisson-gamma and ordered multinomial logit models as well as modeling results from a full Bayes estimation method, are presented. From the modeling results, a preliminary benefit–cost analysis is described, in conjunction with some sensitivity analyses, for developing the guidelines for concrete and high-tension-cable barriers. A discussion of the limitations of this study and potential future extensions is provided.

In recent years, many state departments of transportation have had to modify their approach guardrail–to–concrete bridge rail transition systems to comply with the testing requirements of NCHRP Report 350. Generally, these transition systems are designed and tested for use on high-speed roadways. Because no national transition designs have been developed and tested for lower-speed conditions, the same transition standard is typically applied to all roadways regardless of speed. The new transition designs represent a significant increase in installation cost and complexity over some previous designs that were acceptable under NCHRP Report 230. Thus, it may be cost-prohibitive to require use of the same design on all roadways. The purpose of this research was to develop a guardrail–to–concrete bridge rail transition that is suitable for use on lower-speed roadways and that is less expensive and complex than current designs for high-speed roadways. A low-cost transition was successfully evaluated under NCHRP Report 350 Test Level 2 (TL-2) impact conditions. It is considered suitable for use on roadways that have traffic conditions appropriate for the use of TL-2 safety hardware. Use of this system provides significant savings in material and installation cost compared with high-speed (i.e., TL-3) transitions.

The hybrid energy-absorbing reusable terminal (HEART) is a newly developed crash cushion or end terminal to be used in highway safety applications to mitigate injuries to occupants of errant vehicles. HEART is composed of corrugated plates of high–molecular weight, high-density polyethylene (HMW-HDPE) supported on steel diaphragms that slide on a fixed rail. Kinetic energy from errant vehicles is converted to other energy forms through folding and deformation of the HMW-HDPE material. Many previous designs utilized plastic or permanent deformation of plastics or steels to accomplish this goal. However, HEART is a combination of plastic and steel that forms a largely self-restoring and largely reusable crash cushion. Consequently, HEART has a major life-cycle cost advantage over conventional crash cushion designs. HEART was developed through extensive use of finite element analysis with LS-DYNA. The simulation approach adopted for the development of HEART, construction details, and a description and results of crash tests performed so far to evaluate its performance are presented. Also discussed is some of the follow-up work currently under way for approval of HEART by FHWA as an acceptable crash cushion for use on the National Highway System.

The acceleration severity index (ASI) is used to evaluate the potential for occupant risk in full-scale crash tests involving roadside safety hardware. Despite the widespread use of the index across Europe, there is a lack of research relating this metric to occupant injury in real-world collisions. Recent installation of event data recorders (EDRs) in a number of late-model vehicles presents a different perspective on the assessment of the validity of occupant risk based on the ASI. EDRs are capable of electronically recording data such as vehicle speed, brake status, and throttle position just before and during an accident. Of particular interest is the EDR's ability to document the deceleration of a vehicle during a collision event. This research used EDR technology to investigate the correlation between the ASI threshold limits and the potential for occupant injury in crash events. The longitudinal ASI was found to be a good predictor of overall injury, and the intent of the current preferred threshold value of 1.0 appears valid. Limitations include investigation of the longitudinal direction only, lack of injuries on the abbreviated injury scale (AIS) in excess of AIS 3, and no control for occupant compartment intrusion.

The Midwest guardrail system (MGS), developed at the Midwest Roadside Safety Facility, was designed to improve the performance of traditional strong-post, W-beam guardrail systems. These improvements include decreasing the potential for rollover with high center-of-gravity vehicles, decreasing the potential for rail rupture at the splice locations, and decreasing the sensitivity of the system to the installation rail height. However, safe guardrail termination options for the MGS must be developed before the system can be implemented on the roadside. Two end terminal designs, the sequential kinking terminal (SKT) and the flared energy-absorbing terminal (FLEAT), were partially redesigned and crash tested in conjunction with the MGS according to NCHRP Report 350 criteria. The new versions of the terminals were named the SKT-MGS and the FLEAT-MGS to designate them for use with the MGS. To evaluate the performance of the terminals with the MGS, a series of four full-scale crash tests was conducted: two redirection tests, NCHRP Report 350 Test Designations 3–34 and 3–35, and two head-on impacts, Test Designations 3–30 and 3–31. The results from the four crash tests were found to meet all relevant safety requirements. The SKT-MGS and FLEAT-MGS end terminals are the first successfully tested end terminals for use with the MGS.

Washington State Route 20 (SR-20) in Northwest Washington passes through the Deception Pass State Park. The portion of SR-20 within the park was constructed by the Civilian Conservation Corps (CCC) in the mid-1930s. As part of this work, the CCC built a stone masonry bollard and log rail system to delineate the edge of the road and prevent early-model vehicles from leaving the roadway. Because of their age, quality of workmanship, and importance to the surroundings, the park's bridges and log rail are eligible for the National Register of Historic Places. Previous attempts to replace this rail with a crashworthy system were unsuccessful because of the concern that the aesthetic and historic integrity of the park be preserved. A new approach adopted by the Washington State Department of Transportation began with understanding the context of the highway and the concerns of the other stakeholders. In addition, the stakeholders were educated on the safety issues. As a result, a solution was developed and was acceptable to all. The primary solution involved the development of a new barrier that replicated the appearance of the original log rail. This barrier was crash tested in accordance with NCHRP Report 350 TL-2 criteria and is available for use at other locations at which an aesthetic barrier is desired.

Context-sensitive solutions (CSS) is a comprehensive approach to transportation decision making that embraces the philosophy that transportation programs and projects should address the transportation need, be an asset to the community, and be compatible with the human and natural environment. The CSS movement is rooted in years of controversy stemming from the dissatisfaction of concerned citizens, environmentalists, historic preservationists, multimodal advocates, and others in the transportation decision-making process. In 2002 the North Carolina Department of Transportation (NCDOT) signed an Environmental Stewardship Policy that proclaimed, “Our goal is to provide a safe and well-maintained transportation system that meets the needs of customers and supports the development of sustainable, vibrant communities.” NCDOT viewed the CSS approach as a critical element in institutionalizing its stewardship policy and developed the CSS course to encompass the goals of the stewardship policy. To date, more than 1,000 transportation professionals in North Carolina have been trained in CSS. This paper provides insight into the course development process, including course content, participants’ experiences, and recommendations for agencies interested in developing an effective CSS course.

During the past 5 years, there has been a national movement to integrate context-sensitive solutions (CSS) into transportation project planning and design. Applying CSS principles in the long-range planning process would help ensure that projects were CSS friendly from their earliest conception. This possibility has prompted CSS experts to discuss how CSS can be integrated into long-range planning. Two environmental stewardship initiatives under way at the North Carolina Department of Transportation (NCDOT) provide a unique opportunity to explore this area. In the first initiative, NCDOT has a substantial CSS training program in place. To date, nearly 800 staff members and consultants have attended 3-day CSS training courses. In a separate stewardship initiative, NCDOT is redesigning the traditional thoroughfare plan process to create a new comprehensive transportation plan (CTP) process. Although these two initiatives have not been explicitly connected, this discussion examines how CSS principles are embedded in the proposed CTP process. However, substantial technical and institutional challenges must be dealt with before the CSS-based CTP process can be implemented fully. The conclusion of this discussion is that a state-of-the-practice, long-range transportation planning process should incorporate the CSS principles and decision-making characteristics that have been adopted in North Carolina.

Approaches for measuring the performance of a department of transportation (DOT) in using context-sensitive solutions (CSS) are discussed. Empirical evidence indicates that state DOTs around the country are adopting CSS-based project development approaches and that they are also using performance measurement as a management tool. Such agencies, however, have almost no experience in measuring CSS performance. A proposed framework, based on dialogue with key CSS practitioners, could be used by state DOT staff and their stakeholders to develop customized performance measurement programs for CSS. The framework focuses on creating a set of measures that finds a balance between project-level and organization-level issues and between processes and outcomes. Project-level measurement focus areas discussed include use of multidisciplinary teams, public engagement, project problems and needs, project vision or goals, alternatives analysis, stakeholder satisfaction, construction and maintenance, and quality assurance review. Organization-level measurement focus areas include training, manuals, policies, staff motivation strategies, time frame and budget, and stakeholder satisfaction. It is concluded that a tailored, collaborative self-assessment approach to performance measurement that uses a balanced set of project and organizational measures that focus on both processes and outcomes can help DOTs implement CSS within their agencies more effectively.

The Arizona Department of Transportation (DOT) is following an innovative approach called a needs-based implementation plan (NBIP) to improve State Route 179, in Sedona, Arizona. The NBIP process consists of a coordinated, collaborative team effort to assess needs and develop solutions for this corridor. Throughout the process, Arizona DOT has solicited input and involvement from the community by using a variety of methods, such as advisory panels, focus groups, workshops, a website, and charrettes (collaborative planning events with a specific goal and a limited time frame that harness the talents and energies of all interested parties to create and support a feasible outcome). The NBIP process takes a context-sensitive solutions approach by balancing safety, mobility, and the preservation of scenic, aesthetic, historic, environmental, and other community values. A key component of the approach is that citizens play an active role in the planning, design, and construction of the corridor. Working with Arizona DOT throughout the process are the Big Park Regional Coordinating Council, Yavapai County, Coconino National Forest, FHWA, city of Sedona, and Coconino County. The NBIP process is structured around a series of three charrettes: first, a planning charrette, in which the community articulated its core values and long-range vision for the corridor, and a second charrette, in which participants worked in small groups at gaming workshops to build their road. In addition, an evaluation program, which consisted of evaluation criteria and performance measures, was developed to screen planning concepts resulting from the gaming workshop. At two screening workshops and a third charrette, the community screened 12 planning concepts to produce a single preferred planning concept consisting of a greatly improved two-lane facility.

In response to recent and ongoing adaptation of culvert designs to environmentally sensitive installations, inlet loss coefficients and inlet control flow performance data are presented that are specific to environmentally sensitive culvert geometries. A common practice for such culvert designs is to bury the culvert inverts and create a simulated streambed through the culvert. Common cross-sectional geometries of such culverts typically include circular, elliptical, or pipe arch. These buried- or depressed-invert culverts create inlet geometries for which inlet loss information and inlet control flow performance curves have not been developed. Regardless of the method used to design environmentally sensitive culverts, the ability of the culvert to pass the design flood must be determined. In an effort to provide such information, an elliptical smooth-wall culvert with an invert burial depth of 50% was tested under various conditions (e.g., various end treatments, inlet and outlet control, submerged and unsubmerged inlet conditions, and ponded and channelized approach flow conditions) to determine the inlet loss coefficient and flow performance curve characteristics. The test results show that the inlet loss coefficient is relatively independent of both Reynolds number and the ratio of the distance from the inlet invert to the upstream total energy grade line to the culvert diameter (HW/D) and that the inlet loss coefficients for the elliptical culvert with 50% burial depth are approximately equal to the published coefficients for traditional culvert inlets. The inlet control data adapt well to the Form 1 and Form 2 unsubmerged and the submerged equations recommended by FHWA.

More than 47,000 culverts have been installed under the highways of Utah. The Utah Department of Transportation (DOT) maintains these culverts but has no comprehensive system for assessing condition and planning maintenance activities. Utah DOT initiated a study to determine the condition of its culverts by field surveys. The objective was to develop a system of qualitative and quantitative performance measures to assess both the long- and short-term behavior of highway culverts and to support the Utah DOT effort to modify and populate a computerized database designed to store culvert inspection data that can be used for statewide culvert asset management. Culvert management practices currently used by Utah DOT and other agencies are described. A total of 272 culvert inspections conducted during this project showed the inventory to be aging but not generally in need of immediate maintenance. The Utah DOT database, developed to track culvert condition, is effective but could be improved. Improvements would streamline both culvert inspections and priority ranking of culvert repairs. The FHWA system for rating culvert maintenance action was adopted, with a new proposed table for rating thermoplastic pipe. Culvert ratings were adjusted with an importance modifier that focused inspection and maintenance activity on critical culverts with higher consequence of failure. Critical culverts should be placed on a regular inspection schedule, whereas other culverts can be inspected during periodic roadway repaving or rehabilitation. Culvert inspection results will be added to the database to provide more insight eventually into culvert service life than is now possible.

Riprap and concrete stilling basins are often built at culvert outlets to keep high-energy flows from scouring the streambed. Two simple alternatives to large basins are examined: a horizontal apron with an end weir and a drop structure with an end weir. The two designs are intended to reduce the flow energy at the outlet by inducing a hydraulic jump within the culvert barrel without the aid of tailwater. This research examines the jump geometry and the effectiveness of each jump type and proposes a design procedure for practicing engineers. The design procedure is applicable to culverts with approach Froude numbers from 2.6 to 6.0. Both designs are effective in reducing outlet velocity 0.7 to 8.5 ft/s (0.21 to 2.59 m/s), momentum 10% to 48%, and energy 6% to 71%. The design layouts allow easy access for maintenance activities.

“First flush” is a term for the initial period of stormwater discharge from a storm event. Conventional thinking is that the first flush exhibits high pollutant concentrations. The existence of a first flush in highway runoff has been documented through a comprehensive 4-year runoff monitoring from three highway sites in Los Angeles, California. As part of this study, a numeric definition of the mass first flush ratio is developed; it characterizes the normalized mass of pollutants in the first portion of the normalized runoff volume. Mass first flush ratios have been developed for more than 30 conventional water quality parameters, heavy metals, nutrients, and organic pollutants. This study explores the improved performance that some best management practices (BMPs) exhibit when they can take advantage of the high concentrations of pollutants at the beginning of a storm event. A range of hypothetical events corresponding to the observed mass first flush ratios were simulated. These simulations demonstrate that improved mass removal rates are possible when BMPs can be managed to treat a greater volume of the early runoff. For example, it was shown that for pollutants such as total suspended solids, chemical oxygen demand, total organic carbon/compounds, and oil and grease, infiltration basins that can capture the first 20% of the storm volume and bypass the remaining volume can be twice as effective as a practice that treats 20% of the storm volume throughout the entire period of runoff. Similarly, when a seasonal first flush exists, treating the first few storms of the season entirely is more effective than treating a constant volume throughout the season.