Yield Sign Treatment Recommended by Lord et al. Results of chi-squared and normal approximation statistical tests indicated that crash frequencies were significantly reduced in the period after the sites were retrofitted as modern roundabouts. Harwood et al., 1996), in place of the 1994 AASHTO model, is the fact that drivers are commonly observed accepting shorter gaps than those implied by the 1994 AASHTO model. Of the kinematic measures recorded by Shechtman et al. (2007) found that both older and younger drivers may benefit from the implementation of protected left turn phasing at intersections, resulting in less need for hard accelerations to successfully maneuver across oncoming traffic at an intersection (particularly for older drivers), and better lateral control of their vehicles when negotiating intersections. In a set of studies performed by the California Department of Public Works investigating the differences in crash experience with raised channelization versus channelization accomplished through the use of flush pavement markings, the findings were as follows: raised traffic islands are more effective than flush marked islands in reducing frequencies of night crashes, particularly in urban areas; and little difference is noted in the effectiveness of raised versus marked channelizing islands at rural intersections (Neuman, 1985). Table 16 Aging drivers' decreased contrast sensitivity, reduced useful field of view, increased visual search and decision timesparticularly in response to unexpected eventsand slower vehicle control during movement execution combine to put these highway users at greater crash risk when approaching and negotiating intersections. Staplin et al. This is particularly important for the lane use control signs and the exit signs evaluated, because misunderstandings about proper lane use, and placement of exit signs at the exit location may result in last-minute, erratic lane-change maneuvers, and crashes. Mercier et al. or local). Markings commonly called "ladder" crosswalks (seeFigure 36) combine the transverse and continental to also increase visibility to approaching drivers. with limited sight distance involves the following questions: For example, the risk associated with a crest vertical curve with non-standard This fact underscores the focus on manipulations of those characteristics of sign legends that can increase reading distance. A green guide sign is placed over the lane with a street name, route shield, or destination in the top half, and a lane-use regulatory sign in the bottom half. The NCHRP 5-15 recommendation for maintained intensity levels also establishes a need for in-service intensity performance measurement. FHWA requires a formal design exception wherever stopping Sight Distance Restrictions for a Positioned and Unpositioned Left-Turning Driver at an Aligned Intersection with an Opposing Left-Turning Vehicle. By extension, this result would also best match the behavior of drivers 75 and older observed in the field study. The authors noted that the smaller safety effects for the group of urban multilane roundabouts suggests that there may be differences in safety performance for single-lane designs compared to multi-lane designs. In this study, the average walking speed of the older pedestrians was 2.8 ft/s, with a standard deviation of 0.56 ft/s); the average speed of the younger pedestrians was 4.2 ft/s, with a standard deviation of 0.56 ft/s).
