Minimum Clearance Offsets for Providing Desired Stopping Sight Distances at Simple Curves with Variable Operating Speeds

Lateral clearance on the inside of horizontal curves is required by all geometric design guidelines in order to provide at least stopping sight distance. There already exist graphical models, analytical models, and design charts for determining minimum clearance offsets to meet the requirement. Some of these models determine the offsets based on constant design sight distance values on the assumption that drivers negotiate horizontal curves at constant speed. Therefore, those models are suitable for sites where there is no difference in speeds between tangent and curved sections. Past studies have reported that there are sites where drivers decelerate on entering horizontal curves and accelerate on departing from the curves. At those sites stopping sight distance for a given driver varies with driver location due to variable speed. This paper presents an analytical model and a chart for determining minimum offsets needed to provide desired sight distances at horizontal curves with variable operating speeds. At those sites the offsets yield roadside clearance boundaries that have transition arcs with performances that are similar to those of elliptical arcs. Therefore, practitioners may choose to use elliptical equations or equations and the chart developed herein. Results of this study will be of value to practitioners in the area of roadside design.

Interchange Sight Distance and Design: Aspects and Implementation

The primary purpose of an interchange is to enable an appropriate level of access to the freeway in a safe and beneficial way to the driver. It improves road safety and traffic operation by reducing or eliminating traffic conflicts that would occur if grade separation were not provided (e.g. intersection). Crossing conflicts are eliminated and turning conflicts are either eliminated or minimized. The paper focuses on sight distance criteria in the geometric design of interchanges and junctions, specifically, implementation of stopping sight distance (SSD) and decision sight distance (DSD). These issues incorporate implementation of sight distance policy for: ramps’ geometric design, ramp terminals’ components, and basic lanes’ reduction. These sight distance criteria can alleviate safety by reducing conflicts and confusion to the driver and by keeping alignment simple, direct, and consistent. Specifically, DSD affects traffic control and intelligent transportation systems applications.

Analytical Determination of Size and Location of Roadside Horizontal Sightline Offsets for Compound Curves

AASHTO’s guideline for geometric design of highways and similar guidelines require that roadside areas on the inside of horizontal curves be cleared of high objects to provide stopping sight distance. The guidelines have analytical models for determining the extent of clearance, known as the horizontal sightline offset or clearance offset, for simple curves. Researchers in the past have developed analytical models for clearance offsets for spiraled and reverse curves. Very few researchers developed analytical models for available sight distances for compound curves. Still missing are models for horizontal sightline offsets and locations of the offsets for compound curves. The objective of this paper is to present development of analytical models and charts for determining horizontal sightline offsets and their locations for compound curves. The paper considers curves whose component arcs are individually shorter than stopping sight distance. The resulting models and the charts have been verified with accurate values determined using graphical methods. The models and the charts will find application in geometric design of highway compound curves.

Intelligent speed adaptation for visibility technology affects drivers’speed selection along curves with sight limitations

Sight obstructions along road curves can lead to a crash if the driver is not able to stop the vehicle in time.This is a particular issue along curves with limited available sight,where speed management is necessary to avoid unsafe situations(e.g.,driving off the road or invading the other traffic lane).To solve this issue,we proposed a novel intelligent speed adaptation(ISA)system for visibility,called V-ISA(intelligent speed adaptation for visibility).It estimates the real-time safe speed limits based on the prevailing sight conditions.V-ISA comes with three variants with specific feedback modalities(1)visual and(2)auditory information,and(3)direct intervention to assume control over the vehicle speed.Here,we investigated the efficiency of each of the three V-ISA variants on driving speed choice and lateral behavioural response along road curves with limited and unsafe available sight distances,using a driving simulator.We also considered curve road geometry(curve direction:rightward vs.leftward).Sixty active drivers were recruited for the study.While half of them(experimental group)tested the three V-ISA variants(and a V-ISA off condition),the other half always drove with the V-ISA off(validation group).We used a linear mixed-effect model to evaluate the influence of V-ISA on driver behaviour.All V-ISA variants were efficient at reducing speeds at entrance points,with no discernible negative impact on driver lateral behaviour.On rightward curves,the V-ISA intervening variant appeared to be the most effective at adapting to sight limitations.Results of the current study implies that V-ISA might assist drivers to adjust their operating speed as per prevailing sight conditions and,consequently,establishes safer driving conditions.

DEVELOPMENT OF RETINAL STRUCTURE AND VISUAL ACUITY IN JAPANESE FLOUNDER(PARALICHTHYS OLIVACEUS)

The retinal structure and visual acuity in Japanese flounder Paralichthys olivaceus at different stages of development were examined by light microscopy. The resolving power of the retina, the visual axis and the best visual field were estimated based on the distribution of cone cells in the retina. The visual system of the larvae appears poorly developed at hatching. The larvae with total length (TL) of less than 10 mm, have single cones only and the eyes were well pigmented. At 10-11 mm TL, most single cones fused to form double cones, with the single and double cones forming a mosaic pattern. From larvae to early juvenile the retina stretches, the cones increase in diameter and rods increase in number. Based on the highest density of the cones in the ventro temporal region, the visual axis was orientated up forward. The resolving power of the retina in 40-530 mm TL Japanese flounder was found to range from 25.1 to 11.5 min. The results indicated continual improvements in the visual system of the growing fish towards higher resolving power, visual acuity and sensitivity.