distance headway, overtaking...
TRANSCRIPT
Terminology
• Braking distance, Db: distance covered during braking.
• Stopping distance, Ds: distance covered from recognition to stop. Ds = Dr + Db (brake lag time is not considered)
• Reaction time, tr: time elapsed from the recognition of an obstacle to the start of braking. tr ≈ 1 s
• Distance headway, hd :
– In highway code: distance between two sequent vehicles
– In traffic theory: distance between the noses of sequent vehicles
• Overtaking distance, Do: distance needed for performing a safe overtaking (and has to be seen without obstruction to start the overtaking)
Calculation of total distance headway
Description: v: speed; g: gravitational acceleration;
1: friction factor; tr: reaction time;
q: slope (tgα); lveh : vehicle length;
ls : safety distance (spacing)
svehrtotal lltvqg
vD
*
)(**2 1
2
hd > Dtotal
Dtotal = Db + Dr + lveh + ls
stopping distance (Ds)
Reduced distance headway, hR
Default state, moving vehiclesStopped vehicles
vehicle length
safety distance
braking dist. A
braking dist. B reaction dist. B
reduced distance headway
direction
Leading vehicleFollowing vehicle:
Default state, moving vehiclesStopped vehicles
vehicle length
safety distance
braking dist. A
braking dist. B reaction dist. B
reduced distance headway
direction
Reduced distance headway, hR
)(**2*
)(**2 1
2
1
2
qg
vlltv
qg
vh
A
AsBvehArBB
B
BR
-47,5
-45
-42,5
-40
-37,5
-35
-32,5
-30
-27,5
-25
-22,5
-20
-17,5
-15
-12,5
-10
-7,5
-5
-2,5
0
2,5
5
7,5
10
12,5
15
0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5 2,75 3 3,25 3,5 3,75 4 4,25 4,5 4,75 5 5,25 5,5 5,75 6 6,25
Time-distance diagram (example)
sA sB sC sD
t (s)
tbr: braking timetr: reaction time
tbr,A
tr,Dtr,C
tbr,B
tbr,C
tbr,D
tr,B
s (m)
hR
,AB
lvehA+lS
lvehB+lS
lvehC+lS
hR
,BC
hR
,CD
Overtaking distance, Do
I. Start of overtaking
1. B accelerates
II. End of acceleration
2. Moving with constant speed
III. End of overtaking
Do = ?
AB
E
E
A
B
E
A B
lAB0
Acceleration phase (1):
Relative to A:
Constant speed phase (2):
Relative to A :
In total:
Do = ?
AB
E
E
A
B
E
A B
sB1
sA1
lAB0
sA2
lAB1
sB2
lAB2
AB1l 10112
1122
ABABrelB
relB lltv
ta
s
2
11101
10110
1
101
222t
ast
vvtvt
vvs
tvs
AB
A
2t
1
12212
ABvehBsafAB
ABABrelBrelB
lll
lltvs
Overtaking distance, Do
20120212
202
tvvtvtvs
tvs
B
A
EBrelAEBo
EE
sssssD
ttvs 21