Human Factors Guidelines for Road Systems: Second Edition (2012) / Chapter Skim
Currently Skimming:
Pages 74-84
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 74... ...
Acceptable Gap Distance .
|
From page 75... ...
ACCEPTABLE GAP DISTANCE Introduction Acceptable gap distance refers to the size of the gaps in major-road traffic typically accepted by drivers turning from a minor road that provide sufficient time for the minor-road vehicle to accelerate from stop and complete a turn without unduly interfering with major-road traffic operations. A constant-value of time gap, independent of approach speed, can be used for determining intersection sight distance (see AASHTO (1)
|
From page 76... ...
Discussion Safe gap acceptance distances depend on the driver's ability to accurately judge the time available to execute a trafficcrossing maneuver. Chovan, Tijerina, Everson, Pierowicz, and Hendricks (2)
|
From page 77... ...
FACTORS AFFECTING ACCEPTABLE GAP Introduction The factors affecting acceptable gap refer to the driver, environment, and other situational factors that cause most drivers or specific groups of drivers (e.g., older drivers) to accept smaller or larger gaps than they would otherwise accept under normal conditions.
|
From page 78... ...
Discussion Driver age: Several studies have found that older drivers require gaps that are approximately 1 s longer than younger drivers. Some studies also find that older drivers tend to reject more usable gaps than other drivers, which leads to capacity reductions (1, 2)
|
From page 79... ...
SIGHT DISTANCE AT LEFT-SKEWED INTERSECTIONS Introduction Sight distance at left-skewed intersections refers to the available sight distance to the driver's right side for a vehicle crossing a major road from a left-skewed minor road (where the acute angle is to the right of the vehicle)
|
From page 80... ...
Discussion The available sight distances presented in the guideline are calculated based on drivers of restricted-vision vehicles viewing oncoming traffic backwards over their right shoulder. The 4.5° viewing-angle condition represents a driver sitting back fully against the seat, which represents the most restricted viewing-angle condition.
|
From page 81... ...
SIGHT DISTANCE AT RIGHT-SKEWED INTERSECTIONS Introduction Sight distance at right-skewed intersections refers to the available sight distance to the driver's left side for a vehicle crossing a major road from a right-skewed minor road (where the acute angle is to the left of the vehicle)
|
From page 82... ...
Discussion The primary limiting factor for visibility with right-skewed intersections is the drivers' direct field of view based on how far over their left shoulder they can see by turning their body, head, and eyes to the left. This visibility limitation contrasts with left-skewed intersections, in which parts of the vehicle body can obstruct the drivers' view over their right shoulder regardless of how far they can see to the side.
|
From page 83... ...
COUNTERMEASURES FOR IMPROVING ACCESSIBILITY FOR VISION-IMPAIRED PEDESTRIANS AT ROUNDABOUTS Introduction This guideline identifies countermeasures for improving accessibility for vision-impaired pedestrians at roundabouts. Title II of the Americans with Disabilities Act (ADA)
|
From page 84... ...
Discussion Rumble/sound strips: One study (2) that looked at sound strips in two-lane roundabouts found that they increased the chance that a vision-impaired pedestrian would detect a stopping vehicle and also decreased the time needed to make the detection by more than 1 s.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.