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For heavy duty commercial vehicles it is recommended 4-6 seconds following distance for speeds under 30 mi/h (48 km/h), and 6-8 seconds following distance for speeds over 30 mi/h (48 km/h). [9] Rear-end collisions are the number one type of traffic collisions .
Some authorities regard two seconds as inadequate, and recommend a three-second rule. [4] German law requires a minimum 0.9 second distance but when tested under relaxed conditions [5] researchers found that their test subjects spent 41% of the test time at following distances under 0.9 seconds.
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 affected by the vehicle type and condition, the incline of the road, the available traction, and numerous other factors. A deceleration rate of 3.4 m/s 2 (11.2 ft/s 2) is used to determine stopping sight distance. [6]
Normal individuals have an acuity of 6/4 or better (depending on age and other factors). In the expression 6/x vision, the numerator (6) is the distance in metres between the subject and the chart and the denominator (x) the distance at which a person with 6/6 acuity would discern the same optotype. Thus, 6/12 means that a person with 6/6 ...
Experts historically used a reaction time of 0.75 seconds, but now incorporate perception resulting in an average perception-reaction time of: 1 second for population as an average; occasionally a two-second rule to simulate the elderly or neophyte; [Note 4] or even a 2.5 second reaction time—to specifically accommodate very elderly ...
The second case describes the relationship of horizontal sight distance on safe speed. It is the maximum speed at which a vehicle can come to a full stop before an object, with speed V i, can intercept after having emerged and traveled across the horizontal sight distance "d hsd". Urban and residential areas have horizontal sight distances that ...
4 In or out of the city? 1 comment. 5 Human Psychology and social issues of a safe following distance. 1 comment. 6 Use of Vehicle ... 10 # of "Seconds" rule vs. # of ...
Sight distance, in the context of road design, is defined as "the length of roadway ahead visible to the driver".[1] Sight distance is how far a road user (usually a vehicle driver) can see before the line of sight is blocked by a hill crest, or an obstacle on the inside of a horizontal curve or intersection.