Conference Paper

Preliminary Evaluation of Dynamic Speed Displays with Conditional Messaging

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Article
Flashing yellow warning lights are important for worker and driver safety in work zones. Current standards for these lights do not address whether and how they should be coordinated to provide directional information to drivers navigating through work zones. A field study was conducted to assess driver responses to warning lights. The luminous intensities and flash patterns of warning lights along a simulated work zone were varied during daytime and nighttime. During the daytime, driver responses were relatively insensitive to warning light characteristics, although drivers preferred sequential and synchronised flash patterns over random, uncoordinated flashing. At nighttime, the combination of a temporal peak luminous intensity of 25 cd and a sequential flash pattern was optimal for providing directional information. A single initial warning light having a higher luminous intensity may help drivers detect the work zone without creating unacceptable visual discomfort.
Article
This paper describes an analysis of the effectiveness of dynamic speed display signs (DSDSs) installed in several permanent locations. Sites evaluated included a school speed zone, two transition speed zones in advance of a school speed zone, two sharp horizontal curves, and two approaches to signalized intersections on high-speed roadways. Data were collected before the DSDSs were installed, about one week after installation to determine initial effects of the signs upon vehicle speeds, and again about four months after installation to determine how well the initial speed reductions were maintained. Researchers analyzed average speeds, 85th percentile speeds, and the percentage of the sample exceeding the speed limit. In addition, least-squares regression analyses between the speed of a vehicle upstream of the DSDS and that vehicle's speed measured again at the DSDS were performed to determine whether the sign affected higher-speed vehicles more substantially than lower-speed vehicles. Overall, average speeds were reduced by 9 mph at the school speed zone. Elsewhere, the effect of the DSDS was less dramatic, with average speeds reduced by 5 mph or less depending on the location tested. As expected, those motorists traveling faster than the posted speed limit did appear to reduce their speed more significantly in response to the DSDS than did motorists traveling at or below the posted speed limit. The results of this project suggest that DSDSs can be effective at reducing speeds in permanent applications if appropriate site conditions apply.
Article
Recommendations for implementing speed control at construction and maintenance work zones are presented. The following implementation steps are identified and discussed: (a) determining the need for speed reduction, (b) selecting a reasonable speed, (c) selecting a speed control treatment based on effectiveness, practicality and cost, and (d) selecting a location for the speed control treatment implementation. Four speed control approaches are studied: flagging, law enforcement, changeable message signs, and effective lane width reduction. The advantages and disadvantages of each of these approaches are discussed. Limited cost data for each of the approaches are also presented. The conclusions and recommendations are based on the results of field studies and observations at numerous street and highway work zones in Texas.
Article
Motorists yielding to a pedestrian at the crosswalk line can screen the view of the pedestrian crossing in front of them. This places the pedestrian at risk from vehicles approaching in adjacent travel lanes. An experiment was conducted in which advance yield markings and a symbol sign prompting motorists to yield to pedestrians at the markings were placed at several intersections. Their effects on pedestrian safety at multilane crosswalks with pedestrian-activated yellow flashing beacons were evaluated. Motorist and pedestrian behaviors measured throughout the experiment included the following: occurrence of motor vehicle-pedestrian conflicts that involved evasive action, distance before the crosswalk that motorists stopped when yielding to pedestrians, and percentage of motorists yielding to pedestrians. The introduction of the markings and the sign 10 m before the crosswalk increased the distance in front of the crosswalk that motorists yielded to pedestrians and it markedly reduced the percentage of motor vehicle-pedestrian conflicts. Placing markings 15 m and 25 m in advance of the crosswalk produced similar benefits, demonstrating that treatment effects can be produced over a wide range of values.
Article
Abstract: Variable speed limit (VSL) can be used on freeways to manage traffic flow with the goal of improving capacity. To achieve this objective, it is necessary that both speed and density dynamics be represented accurately. In this study, to deeply understand the effectiveness of VSL control, an analytical model was developed to represent drivers’ response to updated speed limits and macroscopic speed dynamical change with respect to changeable speed limits. Specifically, to model the freeway links having VSL control, the fundamental diagram (FD) was replaced with the VSL control variable in the relaxation term of the METANET. This modification led to the speed control variable appearing linearly, which is preferable for online computation. The density dynamics are based on the cell transmission model (CTM), which is introduced to estimate the transition flow among successive links with some practical constraints. It also offers flexibility in designing active bottleneck in which there is a capacity drop once feeding flow exceeds its capacity. To exploit this benefit, a modification was introduced in the FD of the density dynamics. A VSL control strategy was proposed that explicitly considers traffic characteristics at active bottleneck and its upstream-downstream segments. It can control traffic flow into any type of active bottleneck. Then, the proposed traffic dynamics with the control strategy are implemented in a freeway corridor using the model predictive control (MPC) approach. The analysis was carried out in the calibrated microsimulation model, VISSIM, within a scenario in which shock waves were present. The microsimulation model functions as a proxy for the real-world traffic system. This study reveals that, in terms of mobility, VSL is mostly effective during congestion periods. DOI: 10.1061/(ASCE)TE.1943-5436.0000507. © 2013 American Society of Civil Engineers.
Article
Although law enforcement is an effective way to manage speeds, it requires significant resources to ensure adequate spatial and temporal compliance. In some cases, alternative speed management methods may be necessary to deter drivers who travel faster than the posted speed limit. One such method is through the use of dynamic speed display signs (DSDSs) that help motorists self-enforce their speed. DSDSs measure the speed of approaching vehicles and communicate the speed to drivers on a digital display. The Pennsylvania Department of Transportation invested in several portable DSDSs and selected several locations to use them along two-lane, rural highway transition zones. Transition zones are longitudinal roadway sections that contain changes in the posted speed limit; they are commonly encountered in Pennsylvania where high-speed, two-lane highways pass through rural communities. The section of highway that passes through the rural community has a lower posted speed limit than the upstream, high-speed section of the highway. A before, during, and after observational study of free-flow vehicle operating speeds was undertaken at 12 transition zones to determine the effectiveness of DSDSs. The results of the analyses indicate that the DSDSs are effective in reducing free-flow passenger car operating speeds by an average of 6 mph (10 km/h) while in place and activated. However, the speed reductions observed while the DSDSs were in place faded after the devices were removed from the study sites.
Human Factors Guidelines for Road Systems, Second Edition
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Evaluation of I-75 Lane Closures
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