Transcript 幻灯片 1

A QUANTITATIVE MODEL OF ROAD-SURFACE SAFETY
Jiangbi Hu,
Transportation Research Center, Department of Civil
Engineering,Beijing University of Technology, China
2011.5.
Contents
• Introduction
• Safety factors in the interaction between
vehicle and pavement
• Pavement performance and traffic safety
• Pavement safety model
• Model validation
• Conclusions
1.INTRODUCTION
• Road traffic system is a dynamic and complicated
system , which provides safe, comfortable and
economic road condition for road customer
• Road(include its structures) condition is an
important reason that causes the traffic accident
and has caused accidents up to 30% along with
driver interaction.
1.INTRODUCTION
• Driver safety is associated with surface roughness
and skid resistance.
• The friction is the basic parameter that limits
vehicle speed, stability and effects traffic safety
and driver comfort.
• In many countries standards, there are the
minimum f value for new and maintained road.
1.INTRODUCTION
• The minimum permissible f ranges from 0.6 in
Belgium to 0.4 in France.
• Construction standards in the former SU f is
determined by the expected traffic conditions
and type of use. In dangerous sections: smallradius curves etc. f≥ 0.6; good conditions: f ≥
0.45, ordinary conditions, f ≥ 0.3.
1.INTRODUCTION
• In China, pavement skid resistance conditions
research began in the 1980s, in 1996 SRV tested by
a static pendulum skid-resistance tester was
introduced.
• SRV limit an acceptable range, with no allowance
for different pavement conditions.
• SRV of secondary roads is 47–50, with a SMTD of
0.4–0.6 mm.
2.SAFETY FACTORS BETWEEN VEHICLE AND
PAVEMENT
• Safe operation of a vehicle traveling on any road
must be satisfied for equations (1) and (2):
P  Z  Z  Z j
(1)
Where: P is the vehicle traction force (kg)；Zω、Zψ、Zj
are the air, road, and inertia resistance (kg).
• P is limited to the friction between the tire and
pavement:
P    GK
(2)
Where:GK is the vehicle load; Ψ is the adhesion
coefficient between the tire and pavement.
2.SAFETY FACTORS BETWEEN VEHICLE
AND PAVEMENT
• In a straight line, the braking resistance is parallel to
the driving direction, longitudinal friction force FR is
involved.
• The front wheels are turned at an angle to the
driving direction, a transverse friction force FT
occurs.
• FR and FT occur simultaneously, the integrated force
should not exceed the maximum friction force F, as
shown in equation(3).
F 2 = F R2 + F T2
(3)
2.SAFETY FACTORS BETWEEN VEHICLE
AND PAVEMENT
FTmax
FT
Fm
ax
forward
FR
FRmax
brake
Figure 1: Friction between tire and pavement
• In Fig1, when Fmax is exceeded the vehicle will
slide.
• Braking suddenly on a curve may cause the
vehicle to exceed Fmax and accident.
2.SAFETY FACTORS BETWEEN VEHICLE
AND PAVEMENT
• Over speed is the major cause of accidents on
curved sections.
• The low f, lack of superelevation on the curves of
one national highway in China causes six sliding per
year.
60
50
40
30
accident
numbers
20
SFC
10
268
263
253
247
241
235
228
221
215
208
201
195
188
177
162
145
135
129
120
114
107
0
101
Accident numbers(SFC)
70
stake number
Figure 2: Relationship between number of accidents and SFC.
3. PAVEMENT PERFORMANCE AND TRAFFIC
SAFETY
• If the normal reaction forces of the front wheels
drop to zero, the wheels of the front axle may raise
off the ground, resulting the car’s overturning.
• If the normal reaction forces of the rear wheels are
at zero the traction force is lost base on the
adhesion condition, and if the automobile is unable
recover, it may slide.
Accident rate
（％）
150
Rainless day
accident rate
100
50
Rainy day
accident rate
0
39
48
52
Average value of SFC
58
Figure 3:Accident rate versus SFC for rainless & rainy days
3. PAVEMENT PERFORMANCE AND
TRAFFIC SAFETY
• Figure 5 showing SFC changes in kilometers 0–48
of a certain highway in 3 years , opened in
September 1993.
Figure 5: SFC as a function of time and location for a certain expressway
4.PAVEMENT SAFETY MODEL
• Adequate pavement friction is a necessary
condition for vehicles to travel safety.
• According to conditions of the vehicle running
force, f can be divided into:
(1) longitudinal friction coefficient fR
(2) transverse friction coefficient fT
4.PAVEMENT SAFETY MODEL
• To keep the balance between the actual and
expected values, some concepts are introduced :
(1) maximum longitudinal friction coefficient fTmax
(2) allowable longitudinal friction coefficient fTA
(allowed transit friction)
(3)allowable transverse friction coefficient fSA
(allowed side friction)
(4) expected longitudinal friction coefficient fTR
(required transit friction), and expected transverse
friction coefficient fSR (required side friction).
(1) Quantitative safety model for the
longitudinal friction coefficient
• The longitudinal friction coefficient can be
calculated by (7)
(7)
fT  FT / Q
Where:
fT —— the longitudinal friction coefficient
FT —— the longitudinal friction
Q —— the gravity.
(1) Quantitative safety model for the longitudinal
friction coefficient
• fTA is a reliably safe and determined by the
pavement friction-coefficient standard.
• fTmax is the maximum value under special limiting
conditions
• fTR is under the expected operating speed.
• In practice, there is probably a certain standard
deviation ΔfT between fTA and fTR, which is
calculated by(8)
fT  fTA  fTR
(8)
(1) Quantitative safety model for the
longitudinal friction coefficient
• When fTA ≤ fTR, while ΔfT ≤ 0, the pavement safety
performance is “good.”
• When ΔfT > 0 but less than a certain “critical value,”
the pavement safety performance is “relatively
good.”
• When ΔfT > 0 and also more than a “critical value,”
the pavement safety has hidden danger
,
(2) Quantitative safety model for the
transverse friction coefficient
• The transverse friction coefficient value deviation
ΔfS between fSA and fSR, can be calculated by (12)
(12)
f S  f SA  f SR
• When ΔfS ≤ 0, the pavement safety performance is
“good.”
• When ΔfS > 0 but less than a certain “critical value,”
the safety performance is “relatively good.”
• When ΔfS > 0 and greater than a “critical value,” the
pavement is “dangerous.”
5. Model validation
• A certain road in China was divided into three
sections according to pavement age: 16 years, 4
years, and new reconstruction completed in
September 2003.
• In the three sections, the accident-prone portions
and those with skidding accidents are chose as
shown in Table 3.
5. Model validation
• In tested sections, five representative points about
5–10 m apart along the left wheel path in the
driving direction tested by the pendulum apparatus
in table 4.
• Pavement structure type: 3-cm asphalt concrete,
10-cm bituminous penetration, 20-cm gradation of
sand–gravel-doped lime soil.
5. Model validation
• Table 4: Measured pavement friction coefficients
Serial
number
Location
route
characteristic
surface
age of
pavement
FB20
1
1205.800–1206.800
curve
smooth, intact, and level
with ruts in pavement
16 years
32.8
2
1210.000–1421.000
straight-line
segment
smooth, intact, and level
with ruts in the pavement
16 years
33.8
3
1223.448–1224.448
curve
cracks and ruts in the
pavement
16 years
31.5
4
1364.300–1365.300
straight-line
segment
pavement intact
4 years
42.28
5
1361.000–1362.000
straight-line
segment
pavement intact
3 months
57.2
According to pavement design standard, fTA = 47.
Equation (8) for the quantitative model gave ΔfT
values of 14.2, 13.2, 15.48, 4.72, and -10.2
Taking the ΔfT=Min(14.2,13.2,15.48)=13.2 as the
critical value, we obtain FB20 ≥ 47 (ΔfS ≤ 0)
5. Model validation
Effects of appraise
serial
number
1
kilometer number
1205.800–1206.800
route characteristic
curve
age of
pavement
16 years
FB20
safety
32.8
dangero
us
2
1210.000–1421.000
straight-line segment
16 years
33.8
dangero
us
3
1223.448–1224.448
curve
16 years
31.5
dangero
us
4
1364.300–1365.300
straight-line segment
4 years
42.28
good
5
1361.000–1362.000
straight-line segment
3 months
57.2
safe
6. CONCLUSIONS
•
•
•
•
•
The road system must meet the following equation:
Safety: ΔfT ≤ 0, ΔfS ≤ 0,(ΔfT=fTA-fTR, ΔfS=fSA-fSR )
good: 0<ΔfS≤min(ΔfSi), 0<ΔfT≤min(ΔfTi),
Dangerous: ΔfS>min(ΔfSi), ΔfT>min(ΔfTi)
The minimum f for penetration-type asphalt
pavement allowable standards is too low and can
easily contribute to skidding accidents in China.
Thank you for your attentions!