United States Federal Highway Administration Research Articles

Visual Perception and Illusions in a Driving Simulator - Little Cars, Big Signs

One of the tools that the United States Federal Highway Administration uses to evaluate highway infrastructure-signs, roadway markings, and geometric features-is a driving simulator. The nature of the research necessitates that important visual information is perceived similarly in the simulated world as in the real-world. Perceptual mismatches can lead to incorrect assumptions about driver behaviors and understanding of new or novel roadway designs. Because of limitations in simulator projector technology, and the lack of true depth in images projected onto a cylindrical scene, it is often necessary to adjust the size of projected objects. The objects may need to be scaled up or down relative to 1:1 equivalence of image projected on the retina in order to produce a detectable object or a desired apparent distance. For example, to achieve an appropriate legibility distance for highway signs, signs are scaled up to achieve a mean legibility distances of 1 inch of letter height per 60 feet of (simulated) viewing distance. On the other hand, to attain a 1:1 correspondence with real-world following distances between the subject vehicle and the vehicle ahead, simulated vehicles are scaled down to 75 percent of the correct retinal image size. The methods and theories for arriving at these scale factors are described. The need to scale up highway signs is believed to be related to resolution and contrast limitations of current technology projectors. The need to scale down vehicle sizes may be the result of a Ponzo illusion, in which the converging lines of highway lane markings distort the apparent size of vehicles ahead. Before using a driving stimulator to conduct studies of driver perception or behavior in response to out of vehicle stimuli, it is important to examine assumptions concerning the size of projected images and their detectability and perceived distance. Meeting abstract presented at VSS 2015. Language: en

Operational Evaluation of Detection-Control System, A Dilemma Zone Protection Technology

Detection-Control System (D-CS), a dilemma-zone protection technology developed by the Texas Transportation Institute (TTI) for isolated rural high-speed intersections, was evaluated in a before and after study. By detecting vehicle lengths and speeds at locations 800ft to 1000ft (244 m to 305 m) upstream of the intersection; D-CS monitors the approaching vehicles on a lane-by-lane basis and assigns different weights to trucks and cars based on vehicle length. When processing the real time traffic data, D-CS predicts the best time to end the major approach green phase. This paper looks at eight sites in four states for which the United States Federal Highway Administration (FHWA) deployed D-CS. At each site, one week's worth of cycle-by-cycle traffic and video data were collected to assess the effectiveness of D-CS. The analysis results showed that on average, after activation of the D-CS technology, the frequencies of red-light violations, max-outs, and number of vehicles trapped in dilemma zone were reduced by 68%, 9%, and 57% respectively. Based on the results obtained, the research team concluded that larger scale deployment of this technology can improve safety of thousands of signalized intersections that have the desired geometric and traffic conditions under which D-CS is expected to yield a high benefit to cost ratio.

Rheological analysis of multi-stress creep recovery (MSCR) test

It has been known for some time that the current AASHTO M 320-05 specification does not address the true rutting potential of modified asphalt binders. The multi-stress creep recovery (MSCR) test was proposed by the United States Federal Highway Administration to replace the AASHTO M 320-05 high-temperature specification parameter and various SHRP+test methods. The new parameter of non-recoverable compliance, Jnr, is currently being considered as a replacement for the Superpave high-temperature binder parameter of |G*|/sin δ (ω = 10 rad/s) (AASHTO TP 70-09). An investigation of the suggested new parameter in capturing the rutting potential and a rheological analysis of the MSCR test method were carried out for conventional and modified asphalt binders and are reported in this paper. The laboratory wheel tracking test was conducted to study the rutting potential of asphalt mixes prepared with the same asphalt binders. Correlation of the new parameter, Jnr, with rutting in asphalt mixes is briefly discussed. A linear viscoelastic compliance model was developed to describe the MSCR test and is also discussed.

Driving Brake Reaction Time Following Right Ankle Arthrodesis

The purpose of this study was to compare the brake reaction time of patients with successful right ankle fusion to normal volunteers without an ankle fusion. Ten patients who underwent successful right ankle arthrodesis were evaluated using a driving simulator as well as an in-shoe pedobarographic measuring system. Brake reaction time, braking force, peak pressure, contact area, and the center of force between the foot and the brake pedal were recorded. SF-12 scores were obtained from all study patients. A control group of ten age-matched individuals without ankle fusion was included for comparison. Mean brake reaction time for the ankle fusion group (0.42+/-0.14 seconds) was significantly slower than for the control group (0.33+/-0.06 seconds) (p=0.03). The center of force was consistently isolated to the forefoot in the ankle fusion group compared to controls who distributed the center of force over both the forefoot and midfoot. There was no significant difference between the ankle fusion and control groups with respect to braking force, peak pressure, or contact area. The mean brake reaction time following successful right ankle arthrodesis was significantly slower than that of normal controls. However, the fusion group time was still below the threshold for what is defined as a safe brake reaction time by the United States Federal Highway Administration.

The Impact of Intersection Design on the Driving Performance of Adults in the Recovery Phase of a Turn

Driving, an instrumental activity of daily living, requires safe person-environment interactions. The effectiveness (safety) of four United States Federal Highway Administration intersection design guidelines in the recovery phase of a turn was tested on older and younger adults. Using kinematics measures from an instrumented vehicle, drivers negotiating improved and unimproved intersections were examined in Gainesville, Florida. The findings from a 2 × 2 repeated measures ANOVA (within-subject variable = intersection condition: improved versus unimproved; between-subject variable = age: young versus old) yield support for three manoeuvres: extended receiving lane, right-turn channelisation with acceleration lane and left-turn offset, but not for no acute turn angle. One interaction effect (age x intersection) existed and age effects (favouring older drivers) appeared for three manoeuvres, yet showed little practical significance, suggesting that these design guidelines benefit older and younger drivers alike. This study informs occupational therapists that enhancements in the environment have an impact on safer driving, particularly at urban intersections. A replication of the concept of this study, that is, testing intersection design guidelines in the United Kingdom, may generate valuable information on the plausibility of environmental design guidelines and their effects on the driving performance of older and younger adults.

Analysis of noise barrier overlap gaps.

Sound propagation through the gap produced by two parallel vertical barriers with overlapped ends is formulated for traffic noise sources. The analysis identifies both source and receiver regions according to the mechanisms that influence noise propagation in the vicinity of an overlap gap. A method to account for the contributions from the various source regions for a given receiver location is described. The derived method can be implemented using various equations for sound propagation. The results of using equations approved by the United States Federal Highway Administration for traffic noise propagation are given. Uncalibrated predictions are compared with field measurements for up to 30 receiver positions from each of four overlap gaps. The relative importance of contributions from reflected rays to the noise levels at receiver positions is given. The analysis confirms the initial hypothesis that a commonly used strategy of overlapping barriers by an amount equal to two or three times the overlap width is useful for controlling line-of-sight propagation but ignores the substantial effect of reflections.

Highway traffic noise measurements compared to predictions from FHWA’s Traffic Noise Model

In 1998, the United States Federal Highway Administration (FHWA) released a new tool for highway traffic noise prediction and noise barrier design, the Traffic Noise Model (TNM). In order to assess the accuracy and make recommendations on the use of TNM for the FHWA, the Volpe Center Acoustics Facility performed numerous roadside measurements, obtaining over 100 h of traffic noise data from highways around the country. For each site, acoustical, meteorological, and traffic data were collected simultaneously throughout the measurement period. Spectrum analyzers were used to collect 1/3-octave band A-weighted equivalent sound levels, and the microphones were deployed at distances from 50 to 1300 ft from the roadway and at two heights off the ground, the number of microphones used being site dependent. In comparing the measured and TNM-predicted sound levels, results indicate that TNM is, on average, within 1 dB of the measured data for all types of sites combined. Grouping the data by site types shows how well TNM is performing for open (no barrier), acoustically soft ground sites; open, acoustically hard ground sites; and sites with noise barriers.

Development of a pultruded composite material highway guardrail

Abstract Fiber-reinforced polymer (FRP) composite materials are being used to develop products for use as highway appurtenances, such as, sign supports, luminaire supports and guardrails (crash barriers). These structures, that are located alongside highways and roads, are subjected to vehicular impacts and must be designed to be ‘crashworthy’ to ensure the safety of the driving public. This paper reviews an ongoing 10-year research and development program funded by the United States federal highway administration (FHWA) and the United States department of transportation (DOT) to produce a crashworthy composite material highway guardrail system. An overview of the research and development leading to a patented pultruded composite material guardrail is provided.

Traffic noise barrier overlap gap analysis

Sound propagation through the gap produced by two parallel vertical barriers with overlapped ends was formulated for traffic noise sources. The method accounts for sound propagated from vehicle source positions for a maximum of ten roadway lanes. Six receiver regions were considered based on potential receiver locations with respect to a gap. The analysis identified both source and receiver regions according to the mechanisms that influence noise propagation in the vicinity of an overlap gap, which can result in: direct rays, diffracted rays from the top edge of one barrier, diffracted rays from the top edge of both barriers, rays reflected between the barriers, and rays that are both reflected and diffracted. The derived method could be implemented using various equations for sound propagation. The results of using equations approved by the United States Federal Highway Administration (FHWA) for traffic noise propagation are given. Field measurements for up to 30 receiver positions from four overlap gaps were compared with uncalibrated predictions. The equivalent continuous levels, A weighted, were overpredicted by 2–3 dB. When the analysis was based on an octave band characterization of the source, the mean overprediction was reduced to less than 1 dB.

An evaluation of STAMINA 2.0 using the ORNAMENT ground attenuation algorithm

The United States Federal Highway Administration (FHWA) computer program STAMINA 2.0 was evaluated with the ground attenuation algorithm used in the Ontario Road Noise Analysis Method for Environment and Transportation (ORNAMENT). The goal: To determine this method’s potential to improve noise level predictions at receivers located near traffic roadways with barriers in the propagation path. The study of 41 sites indicated that this method reduced the mean overprediction of noise levels from 2.6 dB using STAMINA 2.0 alone, to 0.5 dB using STAMINA 2.0 with the ORNAMENT ground attenuation algorithm.

COST EFFECTIVENESS OF AUTOMATED HIGHWAY SYSTEMS: A CASE STUDY IN ENGINEERING ECONOMIC ANALYSIS OF A NEW TECHNOLOGY

ABSTRACT In 1994, the United States Federal Highway Administration funded a consortium of companies and universities to research and develop automated highway systems (AHS). If carried to completion, an AHS would enable vehicles to travel on limited access highways under full automation. This paper reports on a study completed as part of the FHWA's Precursor Systems Analyses (PSA) program, to assess costs and benefits of AHS. The paper presents the framework for the evaluation of alternative AHS deployment concepts, with respect to life-cycle costs and cost effectiveness. This framework was applied to a range of scenarios on both a highway and national basis. Specific features include: (1) phased approach to AHS deployment, (2) original cost estimates for both the vehicle and infrastructure, under a range of operating scenarios, and (3) extrapolation of results to a national scale, to account for market penetrations and scale economies. While the work is still preliminary in the sense that costs and benef...