I have two questions:
1) In the sight distance formula,
the first part is
Sight Distance = 1.47 x speed x time + (second part of formula)
where is this 1.47 coming from? if we say distance = speed x time, that 1.47 is there for something like a safety factor or something, by making the distance longer? do i need to know how they came up with 1.47? I am taking AM only for transport]
BUT then why for the SI unit version of this ssame formula, they are multiplying speed and time by 0.278? That is less than 1 and reduces the V x t
2) this came up when in a sample question they said "3 second tangent distance between curves" and calculated that distance as 1.47 x 3 x speed. so this is another use of that formula and "3 sec tangent distance between curves" mean simply the distance that the car will travel in 3 seconds? so again it must be 3 sec x speed x that 1.47 factor, which is that same safety factor of 1.47 right?
1) In the sight distance formula,
the first part is
Sight Distance = 1.47 x speed x time + (second part of formula)
where is this 1.47 coming from? if we say distance = speed x time, that 1.47 is there for something like a safety factor or something, by making the distance longer? do i need to know how they came up with 1.47? I am taking AM only for transport]
BUT then why for the SI unit version of this ssame formula, they are multiplying speed and time by 0.278? That is less than 1 and reduces the V x t
2) this came up when in a sample question they said "3 second tangent distance between curves" and calculated that distance as 1.47 x 3 x speed. so this is another use of that formula and "3 sec tangent distance between curves" mean simply the distance that the car will travel in 3 seconds? so again it must be 3 sec x speed x that 1.47 factor, which is that same safety factor of 1.47 right?
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