Stopping Sight Distance
m × a × cos a
m × N = m × W cosa
h a W × sin a
W × cos a
W = m× g
a
l
m × a × cos a - m × m × g × cos a - m× g × sina = 0
Reaction time, t : 2.5 sec.
Friction coefficient of road : 0.4
Gredient, s (+ : up; - : down) : 2.0 %
1st Title : Stopping Sight Distance
2nd Title : Perception time 3 sec, Friction coefficient 0.3, Gredient 10 %
X-axis : Speed, kph
Y-axis : SSD=d1+d2
Speed, V d1 d2 SSD Remark
kph m m m
0 0.0 0.0 0.0 Perception and reaction distance
20 13.9 3.7 17.6 d1 = V·t/cosω, km
40 27.8 15.0 42.8 d1 = 0.278·V·t·cosω, m
60 41.7 33.7 75.4 Braking distance
80 55.6 59.9 115.5 d1 = V^2/[g·(u± s/100)], km
100 69.4 93.6 163.1 d2 = 0.039·V^2/[g·(u± s/100)], m
120 83.3 134.8 218.2 Total distance
140 97.2 183.5 280.8 dt = d1 + d2 = SSD
160 111.1 239.7 350.8 Reaction time, t normally takes 2.5 sec
u is between 0.3-0.6, normally takes 0.4
400.0
350.0 Perception/reaction Braking Total distance 350.8
300.0
280.8
250.0 239.7
218.2
SSD
200.0
183.5
150.0 163.1
134.8
115.5 111.1
100.0 93.6 97.2
75.4 83.3
59.9 69.4
50.0 55.6
42.8 41.7
33.7
17.6 27.8
13.9
3.7 15.0
0.0 0.0
0 20 40 60 80 100 120 140 160
Speed, kph
0.277777778
0.003943061
0.009857653
350.8
7
1
Passing Sight Distance (SSD) on 2-lanes Road
PP1 PP2 PD1 PD2 PP4
OP1 OP2
PP3
d1 d2 d3 d4
PSD = d1 d 2 d 3 d 4
d1 = 0.278 × v1 × t1
d2 = v2 × t2
d3 = 35 to 90 m
2
d4 = × d2
3
Assumptions:
1) Passed vehicle moves with a constant speed.
2) Passing vehicle must decrease its speed and follow the passed vehicle in order to wait for a safe passing.
3) The driver of the passing vehicle will pass the passed vehicle only when there is sufficient distance to
travelling vehicle from the opposite direction.
4) While passing takes place, speed of the passed vehicle must be maintained.
5) When the passing is accomplished, the passing vehicle must keep its path back into the proper lane.
Recommendation by AASHTO (A Policy on Geometric Design of Rural Highway)
Parameter Unit 48-64 64-80 80-96
V1 kph 40 54.3 68.4
V2 kph 56.1 76.5 84.5
a kph/sec 0.63 0.64 0.66
t1 sec 3.6 4.0 4.3
t2 sec 9.3 10.0 10.7
d1 m 44 66 88
d2 m 145 196 251
d3 m 30 55 76
d4 m 96 130 168
dt m 315 447 583
Average passing speed, V1 : 60 kph
Average passed speed, V2 : 50 kph
Average acceleration of passing vehicle, a : 0.63 kph/sec
Preliminary delay time, t1 : 3.6 sec
Right-lane occupacy time, t2 : 9.3 sec
d1 = 0.278·V1·t1 : 59 m
d2 = 1.47·V2·t2 : 820 m
d3 : 100 m
d4 = 2d2/3 : 547 m
dt = D1+D2+D3+D4 : 1,526 m
Sight Distance in 2-lane Horizontal Circular Curvature
C C
PC PT
A B
PT A B
PC X X
D D
R- X R- X
R R R R
q q
S L, or
A - B PT - PC
O O
Obstruction
° ' ""
Deflection angle ( ° , ' , " ) 33 39 38.25
Degree of curvature, Dc 34 10 0.00
Radius of curve, R = 5,729.578/Dc : 167.695 m
Length of curve, L = 100·A/Dc : 98.519 m
Sight distance, S : 80 m
Offset from Center line of road to obstruction, M
Case I; S L
L × ( 2× S-L )
X= : 4.51 m
8×R
Stopping Sight Distance over Creast
g1 -g2
h1 h2
A× S 2
L = S L
A
AASHTO Recommendation
Design speed Stopping
Sight Distance
kph m
40 40
50 60
60 80
70 100
80 120
90 150
100 180
110 210
120 250
Design speed, V : 80 kph
Sight distance, S : 250 m
Gradient, g1•(+: upward, -: downward) : 3.5 %
Gradient, g2•(+: upward, -: downward) : -3.5 %
Height of driver sight, h1 (AASHTO: d1 = 1.15) : 1.15 m
Height of object, h2 (AASHTO: h2 = 0.20) : 0.20 m
A = g2-g1 : -7.0 %
e = A·S/800 : 2.19
Condition S L Not Applicable
L = 2× S -
(200× ( h h ) )
1 2
2
S>L
: 566 m
A No
Use : 566 m
A×S 2
L = S L
A
@VLOOKUP(G33,C21..E29,2)
Passing Sight Distance over Creast
g1
-g2
h1 h2
where h1 = h2 = h ( » 1.15 to 1.40 m)
A× S 2
L = S L
A
AASHTO Recommendation
Design speed Sight distance, m
kph Intermediate Overtaking
40 60 150
50 120 200
60 160 300
70 200 350
80 240 450
90 300 600
100 360 750
110 420 900
120 500 1,100
Design speed, V 80 kph
Sight distance, S 500 m
Gradient, g1•(+: upward, -: downward) 2.5 %
Gradient, g2•(+: upward, -: downward) -2.0 %
Height of driver sight, h1 (AASHTO: h1 = 1.15) 1.15 m
Height of object, h2 (AASHTO: h2 = h1) 1.15 m
A = g2-g1 -4.5 %
e = A·S/800 2.81
Condition S L Not Applicable
800 × h 1,204 m
L = 2× S - ; S>L
A No
Use 1,204 m
Head Light Sight Distance in Sag Vertical Curve
Head light
1o Height of lamp (0.75 m)
where h = 0.75 m
A× S 2
L = S L
A
Sight distance, S : 500 m
Gradient, g1 (+: upward, -: downward) : 2.5 %
Gradient, g2 (+: upward, -: downward) : -2.0 %
A = g1 - g2 : -4.5 %
e = A·S/800 : 2.81
Length of curve, L
Case I; S L Not Applicable
150 35 × S : 1,422 m
L = 2 ×S - ;S >L
A No
Use : 1,422 m