The long-term effectiveness of Speed Monitoring Displays (SMDs) was evaluated as part of the Midwest States Smart Work Zone Deployment Initiative, a pooled-fund study sponsored by Iowa, Kansas, Missouri, Nebraska, and the Federal Highway Administration. Three SMDs were deployed for a five-week period along a 2.7-mile section between two work zones on I-80 near Lincoln, Nebraska. The mean, 85 th percentile, and standard deviation of vehicle speeds, and the percentage of vehicles complying with the 55-mph speed limit and the 60 and 65-mph speed thresholds were used as measures of effectiveness (MOEs). The SMDs were found to be effective in lowering speeds, increasing the uniformity of speeds, and increasing speed-limit compliance over the five-week period. Statistically significant improvements in speed parameters and speed-limit compliance were observed at the measurement points downstream of the first two SMDs. The improvement in standard deviation and some compliance percentages were not statistically significant at the third SMD. Greater speed reductions and compliance increases were observed for passenger cars than for other vehicles. The combined long-term effect of the three SMDs was also assessed using spatially aggregated MOEs. Statistically significant improvement was found in terms of both speed reduction and speed-limit compliance. One week after the removal of the SMDs, there were still statistically significant speed-reductions and compliance increases, although they were less than during the deployment.
Circular horizontal curves on rural two-lane highways in Nebraska with posted speeds of 55, 60, and 65 mph were investigated to determine the relationship of design and operating and posted speeds in an effort to provide guidelines for consistent roadway design along horizontal alignments. The mean, 85th percentile, and 95th percentile speeds; upper limit of the 16-km/h (10-mph) pace; and percent of vehicles within the pace of free-flowing passenger cars in dry, daytime conditions were analyzed at tangent approach and curve midpoint locations. Highway design guidelines suggest that the posted speed should represent the 85th-percentile speed of the vehicles using the facility and that the roadway alignment should be designed to support the 95th percentile speed. Multiple regression analysis was used to develop prediction equations for the mean, 85th percentile, and 95th percentile speeds at approach and curve midpoint locations. At the midpoint, the deflection angle and length of curve influenced the mean, 85th percentile, and 95th percentile speeds. As the posted speed increased so did the mean speed; as the approach grade increased, the 85th percentile speed decreased; and as the average daily traffic (ADT) increased, the 95th percentile speed decreased. Inferred design speed based on the 2001 AASHTO model does not appear to have an influence on 95th percentile operating speeds in Nebraska. At the approach locations, the 85th percentile and 95th percentile speeds were influenced by posted speed and ADT. The majority of drivers tend not to significantly reduce their speed when traveling from a tangent segment to a horizontal curve (for curves with radii greater than 350 m [1,146 ft]).
Conventional traffic control plans for lane closures of rural Interstate highways normally work well as long as congestion does not develop. However, when the traffic demand exceeds the capacity of the work zone, queues may extend back past the advance warning signs, often surprising approaching traffic and increasing the accident potential. Also, smooth and orderly merging operations may be lost as some drivers remain in the closed lane attempting to squeeze into the open lane at the head of the queue, while other drivers try to prevent drivers in the closed lane from passing them by straddling the centerline or traveling slowly in tandem with another vehicle in the closed lane. These maneuvers tend to reduce the capacity of the merging operation and increase the accident potential and road rage among drivers. Early merge and late merge are two forms of merge control designed to deal with these problems. However, these approaches have operational characteristics that limit their effectiveness under both congested and uncongested traffic flow conditions. The advantages and disadvantages of each approach are examined. A new concept called the dynamic late merge is described, which features the integration of the late merge and conventional lane-closure merge control on the basis of real-time measurements of traffic conditions in advance of the lane closure.
We review the security requirements for vehicular communication networks and provide a critical assessment of some typical communication security solutions. We also propose a novel unconditionally secure vehicular communication architecture that utilizes the Kirchhoff-law-Johnson-noise (KLJN) key distribution scheme.
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