International Journal of Civil Engineering and Technology (IJCIET)
Volume 8, Issue 5, May 2017, pp. 492–499, Article ID: IJCIET_08_05_056
Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=5
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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Scopus Indexed
DEFICIENT SHOULDER WIDTH AND ITS
INFLUENCE ON ROAD CRASH FREQUENCY
ON RURAL HIGHWAYS
Dr. A. K. Sharma
Civil Engineering Department, RCOEM - Shri Ramdeobaba College of Engineering and
Management (RCOEM), Nagpur, Maharashtra, India
Dr. P.D. Pachpor
Civil Engineering Department, RCOEM - Shri Ramdeobaba College of Engineering and
Management (RCOEM), Nagpur, Maharashtra, India
Prof. T.K. Rao
Civil Engineering Department, RCOEM - Shri Ramdeobaba College of Engineering and
Management (RCOEM), Nagpur, Maharashtra, India
ABSTRACT
The aim of this research is to develop crash-prediction models for rural highways.
The total of 1100 accident data is collected over a stretch of 160Km of road length
from national Highway No.6 of India in State of Maharashtra. The Negative Binomial
and Zero Inflated Negative binomial regression techniques are used to develop crash
models. Shoulder Width Deficiency (SWD), Speed variation (LOSC), Percentage of
heavy vehicles (POHV), and Volume of non-motorized vehicle (NMV) are selected as
explanatory variables. It is observed that variables like shoulder width deficiency,
longitudinal oscillation and proportion of heavy vehicles in traffic stream have
significant impact on rural highway safety. The ability to predict accident rates is very
important to transportation planners and engineers, because it can help in identifying
hazardous locations, sites which require treatment.
Key words: Crash Rate, Shoulder width Deficiency, Negative Binomial, Zero-Inflated
Negative Binomial.
Cite this Article: Dr. A. K. Sharma, Dr. P.D. Pachpor and Prof. T.K. Rao, Deficient
Shoulder Width and its Influence on Road Crash Frequency on Rural Highways.
International Journal of Civil Engineering and Technology, 8(5), 2017, pp. 492–499.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=5
1. INTRODUCTION
Countries road network plays very vital role in economic strategy. Transportation is an
essential ingredient of almost everything mankind does to supply itself with necessity of life.
Countries with inadequate means of movement are characterized by low standard of living.
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Deficient Shoulder Width and its Influence on Road Crash Frequency on Rural Highways
People, roads and vehicles form the important combination all over the world to transfer
themselves or goods from one place to another. Road traffic collisions are becoming a matter
of serious concern throughout the world, in terms of social, health and economic loss. Over
1.2 million people are killed every year globally and over 20 million are injured or crippled.
Developing countries accounts for up to 85% of all the fatalities. The problem is particularly
acute in the Asia-pacific region, which has only 16% of the world’s motorized vehicle fleet
but accounts for 44% of global road death. Around 2, 40,000 people die in road crashes every
year in South Asian countries. Driving or riding on an Indian Road in no more an enjoyable
experience. The magnitude of road accidents in India is increasing at an alarming rate and
Indian roads are becoming death traps.
The latest annual statistics states that over 1, 46,000 people are killed on Indian roads.
National level of fatalities per km is 0.025. The rural highway of developing countries
accommodates heterogeneous traffic which includes many types of non-motorized vehicles
other than regular traffic combination. Populations from developing countries are exposed to
high risks of injury and death from road crashes owing this mixed traffic conditions. Along
with shoulder width deficiency (SWD), other explanatory variables used in this study are
speed variation (LOSC)), percentage of heavy vehicles (POHV), and volume of nonmotorized vehicle (NMV). The success of safety improvement programs in reducing accident
occurrence depends on the availability of methods that give reliable estimates of the safety
level associated with existing road locations or proposed plans and designs. Several
approaches exist for estimating safety ranging from simply using accident rates to accident
prediction models which relate the expected accident frequency at a road location to its traffic
and geometric characteristics. Several researchers have shown that the relationship between
accident frequency and exposure is frequently nonlinear, which indicates that accident rates
are not appropriate representatives of safety. This finding has led most safety researchers to
discard the use of accident rate as a measure of road safety and currently, accident prediction
models constitute the primary tools for estimating road safety. Accident prediction models
(APMs) are statistically developed mathematical models that relate the occurrence of traffic
accidents to the traffic and geometric characteristics of the road. These models, the vast
majority of which are negative binomial regression models, are of considerable importance to
highway agencies since they can be used to conduct many traffic safety studies.
2. METHODOLOGY
This study aims to develop models to quantify the impact of road geometry and traffic
variables on crash rate. The study methodology consists of collecting past accident data,
highway geometric data and traffic data and statistically analysing it. The road chosen for this
study was National Highway no.6 in India near Nagpur City which was a two lane undivided
facility during the study period.
3. DATA COLLECTION AND ANALYSIS
The data in this study comprise six years of accident data, collected from 160 km of road
length on National Highway no.6.from police stations and insurance companies. Road
geometry and traffic data was collected through field studies and traffic count survey. For the
purpose of collecting road geometry data, the road was divided into segments of similar
characteristics. Data were collected from 201 segments. Video camera was installed to
measure transverse oscillation of vehicles, and image processing technique was used to
measure the magnitude of oscillation of vehicles.
Preliminary analysis of the data showed positive relations of many of the selected
independent variable with dependent variable. The analysis suggested that the, crash rate is a
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Dr. A. K. Sharma, Dr. P.D. Pachpor and Prof. T.K. Rao
25
5
20
4
15
3
10
2
5
1
0
0
1
21
41
61
81
C-RATE
LOSC
function of shoulder width deficiency, percentage of heavy vehicles in traffic stream, and
longitudinal oscillation of vehicles (Speed variations).Figures 1 to 3 illustrates relationship of
independent variables with crash rates.
101 121 141 161 181 201
LOSC
C-RATE
Figure 1 Relationship of longitudinal oscillation with crash rate
5
3.5
3
SWD
2
3
1.5
2
1
C-RATE
4
2.5
1
0.5
0
0
1
21
41
61
81
101
121
SWD
141
161
181
201
C-RATE
50
5
40
4
30
3
20
2
10
1
0
0
1
21
41
61
81
101 121
POHV
141 161 181
C-RATE
POHV
Figure 2 Relationship of shoulder width deficiency with crash rate
201
C-RATE
Figure 3 Relationship of percentage of heavy vehicles with crash rate
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Deficient Shoulder Width and its Influence on Road Crash Frequency on Rural Highways
4. VARIABLES
The total numbers of crashes per year per km (c-rate) was selected as dependent variable, and
after the preliminary analysis of the data following highly influential parameters were
selected as independent variable.
Longitudinal Oscillation (losc): Speed is one of the major parameter that is used as an
indicator of traffic performance. The variation in the speed of vehicles in a traffic stream is
one the factors that can affect road safety. The data collected showed a wide variation in the
spot speed from 25kmph to 70kmph. The variation in speed with respect to modal average is
taken as longitudinal oscillation in this study.
Shoulder width Deficiency (swd): Shoulder provides an area along the highway for vehicle
to stop during emergency. It is also considered as recovery area for drivers’ error. A report by
Zegeer et al.(1987) indicated that a paved shoulder widening of 2 feet per side reduces
accidents by 16%. Shoulder width deficiency from a standard minimum (5m in this study
inclusive of both sides) can be a factor with significant influence on safe operations of traffic
and hence selected as a variable.
Percentage of heavy Vehicles (pohv): There are two main traffic related issues associated
with commercial vehicles, namely: delays that they may cause to other vehicles and the safety
related impacts. It has been suggested by a number of authors that the presence of a truck in
front of any other vehicle may result in the driver being more cautious due to the large size of
the vehicle and the diminished sight distances.
Volume of Non-motorized vehicles: Presence of Non-motorized vehicles in a traffic stream
may cause frequent changes in speed of other vehicles, frequent sideways movements of
motorised vehicles and minimised driving comfort level to fast moving vehicles.
4.1. Quantifying the Variables
Stochastic modelling techniques are used for quantifying the effects of variables on crash rate
in this study.
This paper presents models built using and Negative binomial regression (NBR) and Zero
Inflated Negative Binomial Regression (ZINBR)
Modelling form used in this study is
Predicted Frequency = ε *p(y), where ε is exposure term, and p(y) is probability of y no.
of accidents.
Linear predictor of accident rate=
+
+
+ −−−−
, and mean value
of accident rate (λ) is given by , log(λ)= +
+
+ −−−−
.
5. CRASH MODEL
The analysis of data was done using SPSS software. Twelve models were developed using
different combination of variables using 1143 accident data collected from different sections.
Data illustrates that 146 segments out of 201 were having zero accidents. Based on statistical
significance five best models were selected. The analysis demonstrated strong relationship
between crash rate and shoulder width deficiency. Performances of the two modelling
methods selected are shown in figures no.4 to 7
Bayesian Information Criteria (BIC) is used to judge the performance of the model.
Smaller BIC values suggest that likelihood of getting the desired output is more and model
performance will be better.
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Dr. A. K. Sharma, Dr. P.D. Pachpor and Prof. T.K. Rao
160
140
No of segments
120
100
80
Predicted Frequency
60
Observed Frequency
40
20
0
-20 0
2
4
6
8
10
12
Accident Frequency
Figure 4 Predicted vs Observed frequency (Negative Binomial)
160
140
No of Segments
120
100
Predicted Frequency
80
Observed Frequency
60
40
20
0
-20 0
5
10
15
Accident Frequency
Figure 5 Predicted vs Observed frequency ( Zero Inflated Negative Binomial)
160
model-I
No. of segments
140
model-II
120
100
model-III
80
model-IV
60
model-V
40
Observed Frequency
20
0
0
1
2
3
4
more than 5
Accident Frequency
Figure 6 Performance of Different Models (Negative binomial)
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Deficient Shoulder Width and its Influence on Road Crash Frequency on Rural Highways
160
model-I
No. of segments
140
model-II
120
model-III
100
80
model-IV
60
model-V
40
Observed Frequency
20
0
0
1
2
3
4
more than 5
Accident Frequency
Figure 7 Performance of Different Models (Zero Inflated Negative binomial)
Negative Binomial
.
∗
λ=e .
Zero-Inflated Negative Binomial
.
.
=
=0
= 1,2 … …
ℎ
1+
∗
.
∗
.
.
∗
∗
∗
.
.
∗
ℎ
Γ
)
Γ
)(
∗
1
1+
+
Γ(
∗
∗
.
+ (1 −
(1 −
.
(
+ 1) 1 +
∗
1
∗
)
) (
1+
∗
∗
)
6. RESULTS & CONCLUSION
λ is same as in Negative Binomial
This study examined the impact of shoulder width deficiency on crash occurrence on a two
lane undivided rural highway in India. The research employed a 160 km stretch of rural
highway, which was divided in 201 segments on the basis of similarity of road geometry and
other environmental conditions. Models were developed using negative binomial and zero
inflated negative binomial regressions. The results suggest that deficient shoulders along with
speed variations and percentage of heavy vehicles in traffic stream have significant impact
on crash occurrence. The findings from this type of studies may help prioritize the
countermeasures.
Suggestion to improve safety was one of the prime objectives of this study. Accordingly
following suggestions are made to improve safety based on the study results.

Shoulder width Deficiency should be eliminated from both sides of the highway.

Shoulder should be maintained in usable condition.

Encroached shoulder should be made free from encroachment.

Separate lanes for slow moving vehicles are unavoidable at present traffic scenario.

Provision of lay bays should be there at frequent intervals.

Enforcement measures should be imposed for parked vehicles on shoulders, sudden stoppages
of vehicles on carriageway, roadside petty shops, and pedestrians on carriageway.
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Dr. A. K. Sharma, Dr. P.D. Pachpor and Prof. T.K. Rao

Speed limit enforcement is not required only for maximum speed but also for minimum
speed, so that the variation in speed is minimum.

At the planning stage only, lanes separated from motor-way should be provided for
motorcycles, slow moving and non-motorized traffic. This will segregate vehicle with similar
dynamic and static characteristics and more uniform flow will follow.
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