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United States Department of Transportation United States Department of Transportation

Public Roads - January/February 2016

January/February 2016
Issue No:
Vol. 79 No. 4
Publication Number:
Table of Contents

Communication Product Updates

Communication Product Updates

Below are brief descriptions of communications products recently developed by the Federal Highway Administration’s (FHWA) Office of Research, Development, and Technology. All of the reports are or will soon be available from the National Technical Information Service (NTIS). In some cases, limited copies of the communications products are available from FHWA’s Research and Technology (R&T) Product Distribution Center (PDC).

When ordering from NTIS, include the NTIS publication number (PB number) and the publication title. You also may visit the NTIS Web site at to order publications online. Call NTIS for current prices. For customers outside the United States, Canada, and Mexico, the cost is usually double the listed price. Address requests to:

National Technical Information Service
5301 Shawnee Road
Alexandria, VA 22312
Telephone: 703–605–6000
Toll-free number: 1–888–584–8332
Web site:

Requests for items available from the R&T Product Distribution Center should be addressed to:

R&T Product Distribution Center
Szanca Solutions/FHWA PDC
700 North 3rd Avenue
Altoona, PA 16601
Telephone: 814–239–1160
Fax: 814–239–2156

For more information on R&T communications products available from FHWA, visit FHWA’s Web site at, the FHWA Research Library at (or email, or the National Transportation Library at (or email


The Impact of Automated Transit, Pedestrian, and Bicycling Facilities on Urban Travel Patterns (Summary Report)

Publication Number: FHWA-HRT-15-015


When the distance between a traveler’s origin or destination and the nearest public transit station is time-consuming, inconvenient, or unsafe to traverse, potential transit riders might be discouraged from using the system. Known as the “last-mile problem,” this distance impedes full usage of existing transit systems, particularly in outlying suburban and exurban areas.

This report summarizes a project funded by FHWA’s Exploratory Advanced Research Program called the Effects of Automated Transit and Pedestrian/Bicycling Facilities on Urban Travel Patterns. The project explored the viability of using a hypothetical driverless vehicle to improve access to and use of available rapid-transit rail service. Researchers conducted a survey in four metropolitan neighborhoods in Chicago served by commuter rail to explore how residents’ travel preferences might change if an automated community shuttle service was available to bring them to and from the station. The researchers also looked at the potential impact of a package of streetscape improvements to facilitate walking and bicycling to the transit station. The neighborhoods differed in levels of population density, current rail use, land use, and affluence.

Researchers used a telephone and mail survey to determine residents’ current travel patterns and preferences with potential improvements. Using agent-based and activity-based modeling, they then predicted a possible 39 percent decrease in car use and a 34 percent increase in commuter rail use after the improvements. The shuttle service produced greater changes in lower density neighborhoods, with forecasted transit use doubling there.

The project also explored travelers’ perceptions of cost, time, and safety. The report discusses differences among communities’ responses to improvements and their implications for the relative effectiveness of each potential improvement. To better understand significant shifts in travel and mode choice, followup research will need to replicate this study, validate its forecasts, and refine the research models.

The report is available to download at


Evaluation of Long-Term Pavement Performance (LTPP) Climatic Data for Use in Mechanistic-Empirical Pavement Design Guide (MEPDG) Calibration and Other Pavement Analysis (Report)

Publication Number: FHWA-HRT-15-019


FHWA’s Long-Term Pavement Performance (LTPP) program uses improved climate data to support current and future research into the effects of regional weather patterns on pavement materials, design, and performance. These data could improve calibration of design tools such as the Mechanistic-Empirical Pavement Design Guide (MEPDG). This report includes the results of an evaluation of climate data from the National Aeronautics and Space Administration’s Modern-Era Retrospective Analysis for Research and Applications (MERRA) project. MERRA provides continuous hourly weather data from 1979 to the present, including observations based on ground, ocean, atmospheric, and satellite elements.

Researchers compared MERRA data against the best available ground-based observations both statistically and in terms of effects on pavement performance as predicted using the MEPDG. Statistical analyses compared data from operating weather stations and MERRA, evaluated the correctness of certain calculations made using the MEPDG, and compared MEPDG-based predictions of pavement performance using weather station data versus MERRA climate data.

Researchers found that MERRA climate data were as good as, and in many cases substantially better than, equivalent ground-based weather station data. Given the benefits and few, if any, significant limitations, the researchers recommend MERRA as the future source for climate data for the LTPP program. The report includes suggestions for incorporating hourly MERRA data into the LTPP database.

The report is available to download at


Safety Evaluation of Access Management Policies and Techniques (Technical Brief)

Publication Number: FHWA-HRT-15-038


Access management is the process that provides access to land development while preserving the flow of traffic on the surrounding road network for safety, capacity, and speed. Although operational effects of access management have been investigated quantitatively through various modeling and analysis approaches, more scientifically rigorous evaluations are needed. This technical brief discusses a study to fill research gaps and quantify the safety impacts of decisions regarding corridor access management.

Researchers developed corridor-level crash prediction models to estimate and analyze the safety effects of selected access management techniques for different area types, land uses, roadway variables, and traffic volumes. They collected detailed data on more than 600 miles (966 kilometers) of corridor across four regions of the United States to facilitate the model estimation process. Because of the strong correlations among many of the variables of interest, such as posted speed limit and number of signalized intersections per mile, it was not possible to develop a single model for each scenario. As a result, the researchers estimated 41 crash prediction models for specific land-use and crash-type scenarios. In most cases, they presented multiple models for each scenario.

Part of the project involved developing functional specifications to create a software tool that can evaluate safety and help users select and apply an appropriate model or set of models. Specifications for the tool include a detailed description of the model selection process and identification of the required and optional inputs, as well as default values for the various scenarios included in this study.

The results will help planners better understand the safety implications of their decisions related to access management. Users can apply the models to assess the relative safety effects of one or more contemplated strategies or combinations, or they can compare the benefits and costs of two or more alternative strategies or combinations.

This technical brief is available to download at


Safety Evaluation of Centerline Plus Shoulder Rumble Strips (Report)

Publication Number: FHWA-HRT-15-048


As part of its strategic highway safety effort, FHWA organized a pooled-fund study of 38 States to evaluate low-cost safety strategies. One of the strategies selected for evaluation was the combined application of shoulder and centerline rumble strips. This strategy aims to reduce the frequency of crashes by alerting drivers that they are about to leave their travel lane. Prior research looked at the safety effectiveness of shoulder or centerline rumble strips used in isolation, but this is the first to study the effectiveness of the combined treatment.

Researchers obtained geometric, traffic, and crash data at treated two-lane rural road locations in Kentucky, Missouri, and Pennsylvania. To account for potential selection bias and regression to the mean, they conducted an empirical Bayes before-after analysis using reference groups of untreated two-lane rural roads in each State with similar characteristics to the treated sites. The analysis also controls for changes in traffic volumes over time and time trends in crash counts unrelated to the treatment.

Combined results for all States indicate statistically significant crash reductions for all crash types analyzed. The crash type with the smallest crash modification factor (CMF) (the greatest crash reduction) is head-on, with a CMF of 0.632. Run-off-road and sideswipe-opposite-direction crashes have estimated CMFs of 0.742 and 0.767, respectively. For run-off-road, head-on, and sideswipe-opposite-direction crashes combined (collectively, lane departure crashes), the estimated CMF is 0.733.

For all crash types combined, researchers estimated CMFs of 0.800 for all severities and 0.771 for crashes resulting in fatality or injury. They excluded intersection-related and animal crashes from the evaluation. The researchers estimated benefit-cost ratios to range from 20.2 to 54.7, depending on the treatment cost and service life assumption, which varied by State.

This report is available to download at