U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: FHWA-HRT-14-002 Date: January/February 2014|
Publication Number: FHWA-HRT-14-002
Issue No: Vol. 77 No. 4
Date: January/February 2014
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 www.ntis.gov 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:
Requests for items available from the R&T Product Distribution Center should be addressed to:
R&T Product Distribution Center
Szanca Solutions/FHWA PDC
13710 Dunnings Highway
Claysburg, PA 16625
For more information on R&T communications products available from FHWA, visit FHWA’s Web site at www.fhwa.dot.gov, the FHWA Research Library at www.fhwa.dot.gov/research/library (or email email@example.com), or the National Transportation Library at ntl.bts.gov (or email firstname.lastname@example.org).
Publication Number: FHWA-HRT-10-077
Geosynthetic reinforced soil (GRS) structures, such as retaining walls, embankments, and load-bearing foundations, have gained popularity in the United States and abroad for their distinct advantages over conventional structures. For example, GRS structures typically are more tolerant to differential settlement and seismic loading and easier and more cost effective to construct.
This report highlights a study that investigated the composite behavior of a GRS mass. One of two elements that make up a GRS wall, the mass consists of compacted soil reinforced with geosynthetic material. Researchers have conducted many studies on the behavior of GRS structures, but the interaction between the soil and geosynthetic reinforcement in a GRS mass has not been fully examined.
Current design concepts hold that the reinforcement material’s strength and the spacing between reinforcements contribute equally to the performance of a GRS structure. This has encouraged designers to use stronger reinforcement at greater intervals to reduce time and effort in construction.
Researchers at the University of Colorado Denver, in collaboration with FHWA, conducted a series of tests on a large-size generic soil geosynthetic composite to examine the behavior of a GRS mass under well-controlled conditions. The tests clearly demonstrated that reinforcement spacing has a much stronger effect than reinforcement strength on the performance of the GRS mass. The researchers established an analytical model to describe the relative contribution of reinforcement strength and reinforcement spacing. Based on the model, they developed an equation to calculate the load-carrying capacity of a GRS mass and verified the equation using data from their tests and experiments by other researchers. The full results of this study are incorporated in the guidance outlined in the Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide (FHWA-HRT-11-026) for the integrated bridge system.
This report is available to download at www.fhwa.dot.gov/publications/research/infrastructure/10077/index.cfm. Printed copies are available from the PDC.
Publication Number: FHWA-HRT-12-037
A restricted crossing U-turn (RCUT) intersection is a promising treatment used to minimize right-angle crashes where two-lane minor roads intersect with rural four-lane divided highways. This TechBrief compares the operations of an unsignalized RCUT intersection in Maryland with a roughly comparable conventional stop-controlled intersection on the same corridor. It also summarizes the results of several crash analyses for intersections converted from conventional designs to RCUT designs along two four-lane divided highway corridors in Maryland.
The researchers found that fewer traffic conflicts occurred at the RCUT intersection, which eliminates conflicts between vehicles turning left off the highway and vehicles from the minor road turning left onto the highway. The RCUT design that directed left-turning and through traffic from the minor road to turn right and travel to a directional U-turn crossing added about 1 minute to total travel time. Although acceleration lanes are not an intrinsic part of the RCUT design, they were part of the design at the RCUT observed in this study. Drivers who made left or through movements from the minor road appeared to make effective use of them.
Crash analyses, including a 3-year before-and-after study, suggest a decrease in the average number of crashes per year of between 28 percent and 44 percent. The data also suggest that the overall severity of crashes that occurred was lower with the RCUT design than with a conventional stop-controlled intersection. The researchers observed a 9-percent reduction in the proportion of crashes that result in injuries or fatalities.
The observational data and the crash analyses indicate that the RCUT design offers a substantial safety benefit, while the travel time penalty is small. The researchers strongly recommend use of acceleration lanes for right turns and U-turns to reduce traffic conflicts and minimize the delay incurred while drivers wait for acceptable gaps in the mainline traffic.
This document is a technical summary of the report Field Evaluation of a Restricted Crossing U-Turn Intersection (FHWA-HRT-11-067). It is available to download at www.fhwa.dot.gov/publications/research/safety/hsis/12037/index.cfm. Printed copies are available from the PDC.
Publication Number: FHWA-HRT-13-044
The conspicuity of a traffic control device refers to the probability that the device will be noticed. But there is no agreed-upon measure to determine conspicuity. Researchers have suggested various measures including eye fixations, recall, and verbal reports. However, conspicuity is not solely a property of the traffic control device itself; it must include consideration of the surrounding environment. For example, roadside vegetation, outdoor advertising, or location of placement could influence whether a motorist sees the device and is able to take appropriate action in a timely manner.
This report discusses four studies focused on the conspicuity of traffic control devices. Researchers examined the effect on driver behavior and performance of messaging features within the right-of-way in a variety of contexts. The team aimed to compile information to help develop evidence-based guidance supporting more effective communication to roadway users.
The first study used multidimensional scaling, a series of techniques used to identify key factors that characterize drivers’ perceptions of the environments in which the control devices exist. The study revealed that two factors, clutter and predictability, characterized the roadway environments included in the research.
In the second study, researchers recorded drivers’ eye glances to traffic control devices on a 34-mile (55-kilometer) drive. After passing selected control devices, the research team assessed driver recall of a device by asking the drivers to identify it. The study demonstrated that warning signs are seldom glanced at and only about half of them are recalled just 2 seconds after they are passed. About 20 percent of speed limit signs received glances, but drivers were aware of the posted speed limit about 80 percent of the time.
The third study examined drivers’ ability to detect speed limit and warning signs. Researchers found that cluttered backgrounds reduced motorists’ ability to detect speed limit signs, but the detectability of fluorescent yellow-green warning signs was not affected by background clutter.
The fourth study examined the effect of background environment on drivers’ ability to read traffic control devices. Researchers discovered the background had no effect on the readability of speed limit signs and had a small effect on the readability of warning signs.
To fully understand the influence of environment in detection and awareness of traffic control devices, more research is necessary. Multidimensional scaling could be a useful tool in that effort, but other methods of characterizing the environment also are warranted.
This report is available to download at www.fhwa.dot.gov/publications/research/safety/13044/index.cfm. Printed copies are available from the PDC.