Stopping Distance Vision is one of several types of visibility used in road design. This is the worst close distance the driver must be able to see in order for a space to stop before colliding with something on the road, such as pedestrian crossings, stopping vehicles, or road debris. Inadequate visibility may affect the safety or operation of a road or intersection.
Termination of visibility is the distance traveled during two phases of stopping the vehicle: perceptual reaction time (PRT), and maneuvering time (MT). The timing of the reactions is the time it takes for the road users to realize that the reaction is necessary because of the road conditions, decide which maneuver is appropriate (in this case, stop the vehicle), and start the maneuver (release the accelerator foot and press the brake pedal). The time maneuver is the time it takes to complete the maneuver (slow down and stop). The distance traveled during the perception-reaction time and the timing of the maneuver is the required visibility.
The American Association of State Highway and Transportation Officials (AASHTO) design standards allow 1.5 seconds for observation time and 1.0 seconds for reaction time.
The visibility value used in the design is the nearest worst situation. For design, a conservative distance is required to allow the vehicle to run at design speed to stop before it reaches a stationary object in its path. Sufficient time is given for the perception-reaction process, and a fairly low level of deceleration is used. Design's visibility allows drivers below average to stop on time to avoid collisions in most cases.
The driver's perception/reaction distance is calculated by:
- d PRT = 0.278 Vt (Metric)
- d PRT = 1.47 Vt (US Customary)
Where:
- d PRT = distance of perception-reaction of driver, m (ft)
- V = design speed, km/h (mph)
- t = brake reaction time, in seconds
Based on the results of many studies, 2.5 seconds have been selected for reaction times. This time it will accommodate about 90 percent of all drivers when faced with a moderate to moderate road situation. Larger reaction times should be allowed in more complex situations.
The braking distance is calculated by:
- d MT = 0,039 V 2 / a ( Metrics)
- d MT & gt; = 1,075 V 2 / a (US Customary)
Where:
- d MT = braking distance, m (ft)
- V = design speed, km/h (mph)
- a = deceleration rate, m/s 2 (ft/s 2 )
Actual braking distances are influenced by the type and condition of the vehicle, the slope of the road, available traction, and various other factors.
A slowing rate of 3.4 m/s 2 (11,2Ã, ft/s 2 ) is used to determine the visibility of the stop distance. Approximately 90 percent of all drivers reduce more speed than that. These values ​​are in the ability of most drivers to stay on track and maintain steering control. Also, most of the wet pavement surfaces and the most capable braking systems provide sufficient braking power to exceed this rate of deceleration.
Stopping Distance Vision (SSD) is the amount of reaction distance and braking distance
- SSD = d PRT d MT
- SSD = 0.278 Vt 0,039 V 2 / a (Metric)
- SSD = 1,47 Vt 1,075 V 2 / a (US Customary)
Video Stopping sight distance
See also
- Clear Clear Clearance In Front
- Braking distance
- Design speed
- Reaction time
- Road traffic security
- Traffic psychics
Maps Stopping sight distance
References
- Wikibooks: Stopping Distance Vision
Source of the article : Wikipedia
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