Transportation Research Record: Journal of the Transportation Research Board

During the 1960s the American public began to demand transportation projects with less impact on the community and its environment, even at the cost of reduced safety and mobility. Congress enacted laws and established public policy objectives to protect and enhance the nation's environment and cultural resources. More recently, Congress has encouraged flexibility in highway design to accomplish these objectives. AASHTO, TRB, state departments of transportation, and FHWA have developed a process, which has come to be called context-sensitive design/context-sensitive solutions (CSD/CSS), to meld design with these objectives. The process is envisioned to result in a transportation project reflecting community consensus on purpose and need, with project features addressing equally safety, mobility, and protection and enhancement of the natural environment. This vision requires the exercise of flexibility in design—the balancing of competing interests. Some are concerned that increased exposure to tort liability will result should design standards or guidelines become too flexible, because they would fail to treat safety as a paramount concern. This assumes that safety is considered a paramount concern both in transportation design and in tort law. This assumption is shown to be erroneous; Congress has established statutory requirements and public policy clearly demonstrating that safety, while it is a primary consideration in design, is not to be a paramount consideration. Safety should be balanced with mobility, protection and enhancement of the natural environment, and preservation of community values. Some court decisions, particularly in the federal sector, recognize and grant design immunity to policy judgments that balance competing interests in the design process. Ultimately, tort law must coincide with public opinion and public policy to be in the public interest. Therefore, tort law will adjust to accommodate CSD/CSS processes, reducing liability exposure. CSD/CSS decisions must be documented with a view of telling the whole story to juries in future tort litigation. Such documentation will greatly assist agency counsel in explaining and proving the reasonableness of design decisions in the context within which they were made. The CSD/CSS vision, it is believed, will overcome liability concerns, both in the short term and in the long term.

Development, testing, and evaluation of the Midwest Guardrail System were continued from the original research started in 2000. This new strong-post W-beam guardrail system provides increased safety for impacts with higher-center-of-mass vehicles. Additional design variations of the new system included stiffened versions using reduced (half and quarter) post spacings as well as a standard guardrail design configured with a concrete curb 152 mm (6 in.) high. All full-scale vehicle crash tests were successfully performed in accordance with the Test Level 3 requirements specified in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features. The research study also included dynamic bogie testing on steel posts placed at various embedment depths and computer simulation modeling with BARRIER VII to analyze and predict dynamic guardrail performance. Recommendations for the placement of the original Midwest Guardrail System as well as its stiffened variations were also made.

Several new roadside safety appurtenances that can be directly linked to the use of nonlinear finite element analysis with LS-DYNA are being installed along the nation's roadways. These advances can be attributed to FHWA's sponsored research program known as Centers of Excellence in DYNA3D Analysis. Some of the simulation efforts at the Midwest Roadside Safety Facility over the past 10 years are documented to help educate the roadside safety engineer and to promote the use of simulation. Noteworthy progress has been made in the use of LS-DYNA for the design and analysis of roadside safety hardware, and it is believed that a great deal more progress is possible.

Computer simulation and physical testing of posts and guardrail installations were performed to develop a W-beam guardrail system for installation where bedrock is within the normal embedment depth of the posts. Computer simulation was conducted with BARRIER VII to determine optimal post force-deflection properties and the critical impact point for a full-scale vehicle crash test. Physical testing included dynamic testing of posts in various embedment configurations and one full-scale vehicular crash test, which was performed according to the Test Level 3 criteria specified in NCHRP Report 350. Steel W152 X 13.4 (W6 X 9) posts were embedded into an elongated hole drilled into rock and backfilled with ASTM C33 coarse aggregate, size No. 57. The elongated hole was created by drilling three holes 203 mm (8 in.) in diameter on 165-mm (6.5-in.) centers. The full-scale crash test, which was performed with a 2,000-kg pickup truck, was used to verify the safety performance of the design for situations where bedrock is encountered on the surface of the ground. Guidelines based on dynamic post testing were developed for use when the bedrock is encountered at various depths below the surface.

The flail space model, which was developed in the 1980s, has become the standard method for estimating occupant risk in full-scale crash tests involving roadside safety features. The widespread availability of air bags and increased seat belt usage rates in today's vehicle fleet, however, raise serious questions concerning the validity of the model. 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 flail space model. 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. A methodology using EDR data to investigate the capability of the flail space model to predict injury to air bag-restrained occupants and results of a preliminary analysis based on implementation of the developed methodology on a limited data set are presented. Most of the analysis is limited to the occupant impact velocity because of insufficient data for evaluation of the occupant ridedown acceleration. The longitudinal occupant impact velocity was found to be a good predictor of overall injury, chest injury, and, to a lesser extent, lower extremity injury. For the head and upper extremity body region, the longitudinal occupant impact velocity is a weak predictor of injury.

The compliance of a Connecticut-designed and -developed impact-attenuation system, the Narrow Connecticut Impact-Attenuation System (NCIAS), with NCHRP Report 350 guidelines is documented. Background information about the system is given, including information on the performance of field installation locations and the availability and cost of installation. NCHRP Report 350 specifies eight full-scale crash tests for redirective/nongating devices. Three of the eight tests were not conducted on the NCIAS because they are similar to three tests conducted under the NCHRP Report 230 requirements, which the NCIAS passed. The five remaining tests were performed. One test was repeated after one of the cylinders was strengthened. All tests were conducted in accordance with the guidelines of NCHRP Report 350 for Test Level 3 devices. The NCIAS passed all requirements for four of the five test designations. It did not pass the requirements for the reverse hit test; therefore, the NCIAS must not be installed at locations where it may be struck from the reverse direction. FHWA has approved the use of the NCIAS on the National Highway System at locations where reverse-direction impacts are unlikely.

The use of roadside safety barriers in Italy has changed in recent years: the number of installed devices has increased, and so have their stiffness and resistance. These changes were necessary because early barrier design was inadequate to contain and redirect heavy vehicles. The change in barrier design led to an increase in stiffness and resistance; consequently, the action transferred to the structure by the device increased. The need for resistance on the bridge slabs can be too high because the peculiar action of the roadside barriers was not adequately taken into account in the oldest bridge design codes. In addition, characterizing the actions transferred to the bridge slab is difficult because of the dynamic nature of vehicle impacts on roadside barriers. Given the impossibility of performing a full-scale laboratory test for every bridge deck, the use of computational mechanics applied to dynamic impact/interaction problems is one of the best ways to establish these actions in the project phase. Research was conducted into the use of a three-dimensional finite element model of the bridge slab-barrier-vehicle system to perform a numerical simulation of the impact, according to the procedure used for the roadside barrier homologation crash test, described in the European Standard EN 1317.

The safety performance of roadside features may depend not only on barrier but also on vehicle behavior. Best results require efficient synergy of barrier and vehicle, or compatibility. Examples of problems where such compatibility may be needed are discussed. One of these problems—head ejection in collisions with high-containment barriers—was investigated with an accident survey, full-scale tests, and laboratory sled tests. One of the conclusions is that, with high-containment barriers suitable for narrow medians, partial head ejection occurs systematically and may represent a high risk. Head containment in such collisions should be mandatory for crashworthy vehicles. This can be easily obtained with laminated glass, without window frame reinforcement. The conclusion is that vehicle and barrier crashworthiness standards should be linked. Collisions with safety barriers are statistically significant events and should be considered among vehicle passive safety items.

During the post-World War II period, conventional roadway design has been based on a functional classification system that addresses levels of vehicle movement and access to abutting properties. Traffic-carrying capacity has been the dominant consideration. In recent years, more attention has been given to other characteristics of local streets and a small number of major streets. New design standards have been developed for local (neighborhood) streets by some organizations and local agencies. At the same time, the National Environmental Policy Act has increased the importance of environmental considerations in the design of major streets and roads and highlighted the importance of minimizing impacts of roadway projects on natural resources, particularly in rural environments. However, no widely accepted design guidelines have yet been developed for urban major streets. Street design and urban design professionals share a need for a two-dimensional framework that ties together (a) roadway design criteria for an expanded palette of street types (number of lanes; target speed; pedestrian, transit, bicycle, and motor vehicle functions; other functional criteria) and (b) a set of place types that reference features of both the public right-of-way and private development fronting on the roadway and in the broader area. The conventional functional class-based design criteria do not satisfy this need. The basic structure of such a framework is discussed.

The aesthetic character and visual quality of transportation corridors as seen by local and visiting travelers in Minnesota were investigated. Highway corridor landscapes were broadly defined to include the entire "view from the road." This definition is intended to contribute to the substance of context-sensitive design by selecting characteristics of landscapes seen from the road that will be relevant for highway design and planning. It assumes that highway travel experiences can have a significant effect on the perceived attractiveness of the places where people live, work, and travel. The aesthetic initiative measurement system (AIMS) was developed and tested to provide a method for the Minnesota Department of Transportation (MnDOT) to use to understand and monitor how travelers perceive the attractiveness of Minnesota's highway corridors and to inform planning, design, construction, and maintenance decision making with specificity. Development of the AIMS methodology involved MnDOT staff from several disciplines and local citizens in understanding perceptions of the value of Minnesota's highway planning, design, engineering, and maintenance choices. AIMS researched the problem of identifying what landscape characteristics seen from the highway are noticed for their aesthetic quality by travelers. AIMS measured the relative aesthetic value of those characteristics and then used those measurements to document the benefits for design and planning to monitor and compare landscape aesthetic values across space and time.

Eleven road segments in Minnesota were examined in a user survey that addressed road travelers' preferences for physical characteristics, aesthetics, and amenities of that segment. The user survey was based on earlier focus group work. Results indicated that road travelers were able to differentiate between physical and socially derived attributes and amenities associated with a particular roadway. Roads do have character, and users are able to identify and evaluate characteristics specific to each road segment. Many roadway features related to maintaining scenic and environmental qualities were highly valued. Users are not supportive of additional business development along some roadways and prefer instead that activity be clustered in communities located on the road segment. Results also indicated that even though a particular roadway may not have had official scenic designation, user evaluations were similar to those with such designation or even more focused on scenic qualities.

A heretofore overlooked mechanism is described for the removal of sediment in the vicinity of a structure, such as a bridge pier, located in erodible sediment and subjected to water flow. The strength of this mechanism depends on, among other things, the ratio of structure width to sediment grain size, b/D ₅₀. The mechanism results from the pressure gradient field imposed on the bed by the mean flow around the structure. The large pressure gradients created by the structure are confined to a relatively narrow region near the structure. The forces due to the pressure gradients acting on the sediment grains near the structure decrease with increasing values of b/D₅₀. This mechanism helps explain the functional dependence of equilibrium local scour depth on b/D₅₀ observed in both laboratory and field tests. It also explains why, in general, physical model local scour tests tend to overpredict prototype scour depths.

To reduce the current trend of decreasing water clarity of Lake Tahoe, the California Regional Water Control Board's Lahontan Region imposed numeric discharge limits for five pollutants (total nitrogen, total phosphorus, total iron, turbidity, and oil and grease) for both surface water and infiltration discharges in the Tahoe basin. To assess its compliance with these discharge limits, the California Department of Transportation (Caltrans) monitored six representative sites for snowmelt and other storm water runoff from summer 2000 through spring 2003. In addition, Caltrans has investigated several existing double-barrel sand traps for their effectiveness in removing pollutants and complying with the Tahoe basin discharge limits. The results obtained to date indicate that (a) concentrations of pollutants found in the snowmelt runoff are higher than the specified storm water discharge limits; (b) double-barrel sand traps were capable of capturing sand and sediment, but the capture was not complete; (c) particles that range from 100 to 2,000 μm represented the highest proportion, but no correlation was found between particles and chemical concentrations; and (d) sand traps did provide modest improvement in runoff quality, but this improvement was insufficient to meet Tahoe basin discharge limits, and hence additional treatment was found to be needed to bring the effluent water quality into compliance.

Transportation facilities such as parking lots and maintenance yards often do not have provisions to treat storm water before discharge. Catch basin inserts can provide a retrofit alternative as a method to meet the new National Pollution Discharge Elimination System Phase II storm water pollution prevention regulations. Inserts produced by four manufacturers were evaluated for removal of suspended solids and petroleum hydrocarbons by using a pilot scale catch basin and synthetic storm water. In addition, the inserts were placed at operating transportation facilities and monitored for operational problems. At a flow rate of approximately 0.013 m³/s (200 gal/min) and pollutant concentrations for total suspended solids (TSS) and total petroleum hydrocarbons (TPH) of 225 mg/L and 31 mg/L, respectively, the inserts were capable of removing 11% to 42% of TSS and 10% to 19% of TPH.

A 2-year water quality monitoring project was conducted to evaluate the removal of storm water contaminants by existing vegetated slopes adjacent to freeways. Objectives of the study were to generate design criteria and to determine whether standard roadway design requirements result in buffer strips with treatment equivalent to those specifically engineered for water quality performance. Variables such as width, slope, vegetation density, and hydraulic loading were evaluated by studying the runoff through existing vegetated slopes at four locations in northern California and four locations in southern California. At each location, concrete channels were constructed to capture freeway runoff after it passed through existing vegetated strips of varying widths. The quantity and quality of the runoff discharged from the buffer strip were compared with freeway runoff collected at the edge of pavement. Buffer strips consistently reduced the concentration of suspended solids and total metals in storm water runoff. The strips were also effective in removing dissolved metals when the edge of pavement concentrations were sufficiently high. Little or no change in concentration was observed for nitrogen and phosphorus. Concentrations of organic carbon, dissolved solids, and hardness increased. For the constituents exhibiting a decrease in concentration, steady-state levels were generally achieved within 5 m (16 ft) of the pavement edge for slopes commonly found on highway shoulders and where the vegetation coverage exceeded 80%. Slope, vegetation type and height, highway width, and hydraulic residence time had little or no impact on the discharge concentrations.

With the proliferation of utilities within the right-of-way (ROW) of highway facilities, transportation agencies around the country are finding it increasingly difficult to allow more utilities into the ROW and, at the same time, manage their own transportation systems effectively. Outstanding issues related to the utility permitting process at transportation agencies are outlined, a prototype online utility permit data management system that supports data transfer and map-viewing capabilities is described, and recommendations for implementation are discussed and formulated. Three goals drove the development of the prototype: to automate the utility permit data entry process, to reduce utility permit processing turnaround times and paperwork substantially, and to provide a mechanism to help maintain the inventory of utilities within the transportation agency up to date by using the data collected during the utility permitting process. The current status of the prototype is described, and several actions that will assist in the prototype implementation process are outlined. Also discussed are standards and specifications and the need to implement adequate positional accuracy and utility installation documentation procedures, which are rarely addressed in utility accommodation policies or technical specifications for particular projects. Implementing those procedures would result in a number of benefits. Among them are improving the quality of utility data at transportation agencies and utility companies, bringing the installation of utilities within the highway ROW to standards comparable with those of other construction activities within the ROW, facilitating the implementation of roadside safety programs, and contributing to the effective management of the highway ROW.