Transportation Research Record: Journal of the Transportation Research Board

The Virginia Department of Transportation’s (VDOT) Road and Bridge Specifications require that retroreflective sheeting used on construction and maintenance activity signs be a fluorescent prismatic lens type that is retroreflective at entrance angles as great as 50° with observation angles of 0.2° and 0.5°. Because the validity of this requirement was recently questioned, this study was conducted to determine if the specification were appropriate or not. The study results indicate that VDOT’s wide entrance angle requirement is not appropriate for construction and maintenance signs and that observation angles should receive more attention than entrance angles.

Condition-responsive advisory speed messages were evaluated as part of the Midwest States Smart Work Zone Deployment Initiative, a pooled-fund study sponsored by Iowa, Kansas, Missouri, Nebraska, and FHWA. The messages were displayed on three portable changeable message signs (PCMS) placed approximately 1.61 km (1 mi), 4.83 km (3 mi), and 12.87 km (8 mi) ahead of a work zone on a rural interstate highway in Nebraska. The messages were intended to advise drivers of the speed of slower traffic ahead and thereby encourage them to slow down. Speeds downstream of the PCMSs were measured and compared with the speeds displayed in the messages. The results of the analysis indicate that the messages were somewhat effective in reducing speeds. Their effectiveness could have been improved if the distances between the PCMSs had been shorter and thus the message locations would have been closer to the points with lower traffic speeds. Driver interviews revealed that the advisory speed messages were understood and thought to be useful by most drivers who had seen them. However, some drivers questioned their usefulness and doubted their reliability, because they had not seen any reason to slow down.

Work zones tend to cause hazardous conditions for drivers and construction workers, because they create conflicts between construction activities and traffic, thus exacerbating the existing traffic conditions. Every effort should therefore be made to minimize the negative impacts of work zones. A clear understanding of work-zone crash characteristics will help to determine appropriate measures to minimize work-zone hazards. This study investigated the characteristics of work-zone crashes that occurred in Virginia from 1996 through 1999. The information on each crash was obtained from police crash records. Each crash was located in one of five areas of the work zone—(a) advance warning, (b) transition, (c) longitudinal buffer, (d) activity, and (e) termination. The percentage distributions were analyzed relative to crash location, crash severity, collision type, and highway type. The proportionality test was used to determine significant differences at the 5% significance level. The results indicate that the activity area is the predominant location of work-zone crashes regardless of highway type, and rear-end crashes are the predominant crash type. The results also indicate that the proportion of sideswipe-in-same-direction crashes in the transition area is significantly higher than that in the advance warning area.

Until recently, no federal guidance existed on the retroreflectivity of highway signs, and the replacement policy has been left to the discretion of local officials. FHWA has now published a proposed set of minimum retroreflectivity requirements for traffic signs. The proposed minimum retroreflectivity values published by FHWA were compared with retroreflectivity values observed from signs with ASTM Type III sheeting in the state of Indiana. Research found that approximately 4% of signs scheduled for removal in 2000 or 2001 were below the proposed FHWA minimums. Having different retroreflectivity minimums for different speeds and sign sizes unnecessarily complicates the proposed minimums. Using the single most conservative retroreflectivity value for each color would be sufficient.

Research and recommendations were produced on the basis of a study on the development of minimum retroreflectivity values for overhead guide signs and street name signs. The research reviewed the literature and available photometric models. A photometric model was created to develop minimum retroreflectivity values for overhead guide signs and street name signs. One model input was the minimum luminance required for legibility. To obtain minimum luminance requirements for overhead guide signs and street name signs, a field evaluation was performed. Accommodating older drivers was specifically emphasized. After the minimum luminance values were determined, the minimum retroreflectivity model was used to study the impacts of (and determine appropriate values for) factors that affect retroreflectivity, such as distance, headlights, and vehicle speed. After the appropriate values were determined, the minimum retroreflectivity model was executed for the final runs. The recommended minimum retroreflectivity values were grouped into one table that includes overhead guide signs, postmounted street name signs, and overhead (mast-arm– or span-wire–mounted) street name signs. The values depend on type of sheeting, speed, and sign position.

Of critical economic importance to roadway management agencies is the retroreflectivity of edge lines and centerlines and the retention of retroreflectivity with exposure to weather, snowplowing, road salt and sand, and traffic density. This study evaluated factors affecting the performance and durability of painted edge lines and centerlines on specific Michigan roadway sections as part of a project to develop a practical pavement marking management system. An ill-defined aspect of retro-reflectivity is the relationship of glass sphere content and the decay of retroreflectivity over time and from seasonal maintenance. Two techniques were developed to quantify the glass sphere content of retroreflective pavement paints. In the first method, aluminum plates are fastened to the roadway and painted in the field as the painting crew applies the striping. The plates are retrieved and pyrolyzed at elevated temperature, with observations made on weight changes of the painted plate. A mass fraction of glass spheres can then be calculated. In the second method, the painted plates are photographed at low magnifications. The macrographs are converted to a binary image that is evaluated using image analysis software to determine the number of spheres per area, average size, and aerial percent. The glass sphere content, as determined by pyrolysis and image analysis, is correlated with retroreflectivity measurements collected on the same samples. These new methods will lead to a better understanding of factors related to the retroreflectivity loss of pavement paints and ultimately to improved products and maintenance practices.

Because no national guidelines exist on establishing pavement marking service life, the scheduling of road striping has been inconsistent among maintenance agencies. This study establishes a way to set striping schedules that accounts for factors affecting scheduling, mainly application cost, service lifetime, and user cost relative to crashes during the striping lifetime. Striping useful lifetime is defined as the striping age beyond which pavement markings become ineffective in relaying necessary vehicle positioning information, when deteriorated pavement marking retroreflectivity reaches a minimum acceptable value. An exponential regression model was used to depict the relationship between striping age and average daily traffic (ADT), using a retroreflectivity threshold of 150 mcd/m²/1x. Striping useful lifetime was established for ADT levels using exponential regression analysis. Application costs were based on the latest available unit costs from the Alabama Department of Transportation for white and yellow longitudinal stripes of paint and thermoplastic markings. Using the National Safety Council estimates of crash severities, user costs were based on the dollar equivalency of the damage to vehicles and occupants in retroreflectivity-related crashes. The data were extracted from the crash experience of approximately 1,300 mi (2100 km) of state highways in 32 Alabama counties. For use in scheduling striping, paint and thermoplastic striping costs were compared on an equivalent annual basis, accounting for application and user costs. Although the crash data and retroreflectivity data were collected on Alabama roads, the findings and conclusions are applicable to areas of warmer climate where snowfall is uncommon.

Although traffic and weather information systems indicate existing air and road surface temperatures, many drivers want to know not the temperature but the degree of road slipperiness. The friction coefficient is the best index for snow and ice conditions, but it is difficult to calculate. Some weather condition data are closely correlated with the friction coefficient. In this study, the use of weather and traffic data to determine the degree of road slipperiness was examined quantitatively by analyzing field data obtained at an intersection on a trunk line. Two kinds of filters were effective in extracting the slipperiness component from the observed data—the Kohonen Feature Map (KFM) and principal component analysis (PCA). KFM kept the distribution of the observed data uniform by eliminating excessive data, and PCA eliminated multicollinearity among the observed variables. The first two principal components successfully represented the original observed data with an accumulated proportion of more than 0.85. A linear multiple regression model, in which the PCA score values were adopted as the explanatory variable, was also justified. The multiple correlation coefficient was satisfactory for many patterns, and the radiation-related data were effective in improving estimate precision.

Residents were surveyed for their opinions on snow removal operations and the amount of money they would be willing to spend for snow removal service. From the results, basic policies are proposed for future snow removal operations in the four Japanese cities surveyed—Sapporo, Asahikawa, Kushiro, and Kitami, Japan. The results were analyzed by Kishi’s Logit PSM (KLP) to quantify the degree of snow removal desired by residents and the amount of money they would spend for this service. Residents rated maintenance of carriageway width and surface conditions on trunk roads fairly high and wanted significant improvements in snow removal on residential roads. Few residents wanted less snow removal service than they currently received. Most respondents wanted improvements. KLP analysis of the questionnaire results showed that Sapporo was the only city where the standard, acceptable cost to consumers was lower than its current snow removal cost. Many Sapporo respondents said that their current cost was unreasonably high, whereas many Asahikawa, Kushiro, and Kitami residents viewed their snow removal service as inexpensive.

Winter maintenance of pavement surfaces consists of plowing and the application of corrosive deicing agents. These chemicals are hazardous to the environment, and thus their use should be minimal. More than 20 years ago, the Connecticut Department of Transportation (ConnDOT) investigated the use of 2.1 MPa (300 psi) pressurized salt brine jets to enhance deicing performance. Despite promising results from several field trials, technical difficulties led to abandonment of this technology in the early 1980s. Recent advances in high-pressure jetting technology suggest that the use of high-pressure jets in conjunction with improved chemical agents for pavement deicing may now be practical. In this study, the application of modern high-pressure jetting technology to deice pavement is explored. The proposed system removes ice and snow through the combined action of mechanical jetting forces and controlled use of deicing chemicals. Appropriate operating parameters and consumption rates are identified and compared with the ConnDOT system developed in the 1970s.

The environs of Sapporo, Japan, including four cities and three towns, were designated “studded tire restriction areas” by the Studded Tire Regulation Law of 1990. As a result of the law’s enactment, the studded tire usage rate decreased drastically, and the dust pollution from vehicles and dust concentration progressively decreased. The use of studless instead of studded tires had positive effects, such as improvements in air quality and the roadside environment. However, traffic congestion and vehicle and pedestrian accidents increased on slippery roads. The effects of the studded tire regulation were examined with an economic assessment of the 10-year period since the law was enacted. The effects of using studless tires were also assessed for transportation service and the environment. Calculated using the contingent valuation method for environmental evaluation and the primary unit method for transportation service and air quality, the effects were analyzed using the benefit incidence matrix. Positive effects were observed, such as an improved roadside environment for residents and pedestrians and reduced road maintenance expenditures. Adverse road user effects, however, were also observed, including increased travel time and costs.

As an environmentally compatible and cost-efficient alternative for roadside management, soil bioengineering has become increasingly important and attractive. Soil bioengineering uses live plants and plant parts as building materials for engineering and ecologically sound solutions to erosion control, slope and stream bank stabilization, landscape restoration, and wildlife habitats. However, not all decision makers are aware of the specific benefits of this approach. This case study applied a benefit-cost analysis to an experimental soil bioengineering demonstration project to evaluate the cost-effectiveness of soil bioengineering as an alternative to traditional roadside management. Traditional roadside management methods (geotechnical solutions) were used as the baseline, and soil bioengineering treatments were treated as an investment alternative. Cost savings, along with other environmental benefits, were assessed and compared with construction costs. The effects of life cycle, effectiveness, and discounting were included in the analysis to ensure comparability between both treatments. The analytical results demonstrate that soil bioengineering methods, if technically feasible, could be adopted to produce equal or better economic and environmental results. The findings of the research project and the economic analysis indicate that soil bioengineering is an efficient and environmentally beneficial tool for roadside management.