Shad R. et al. Identification of Road Crash Black-Sites Using Geographical Information System
UDC: 656.1.08(55)
007:528.9]:004(55)
007:656.1]:004(55)
DOI: http://dx.doi.org/10.7708/ijtte.2017.7(3).07
IDENTIFICATION OF ROAD CRASH BLACK-SITES USING
GEOGRAPHICAL INFORMATION SYSTEM
Rouzbeh Shad1, Shahriar Rahimi2
1
2
Civil Department, Engineering Faculty, Ferdowsi University of Mashhad, Iran
Civil Department, International Campus, Ferdowsi University of Mashhad, Iran
Received 24 May 2017; accepted 20 July 2017
Abstract: It is a crucial task to reduce road crashes by performing analyses and taking appropriate
countermeasures to save lives. It has been a major issue for many people and government to
reduce the amount of road collisions especially in Iran, since it could be a great threat to this
country. Identification of crash black-sites is one of the most important fields in road safety
studies. Many highway agencies have been using Geographical Information System (GIS)
for analyzing crash data. The GIS based application integrates the information collection
capabilities with the visualization. In this paper, Incident features like location, date, type of
vehicle involved, and number of persons injured or died are imported in the GIS database.
Then, Kernel density is to apply on the prepared data. The main objective is to specify road
crash black-spots considering all types of traffic crashes based on their severity using Kernel
Density through GIS environment. The results show that more severe crashes take place
further from the cities than accidents with only property damages. Also, overlaying all crash
types using the suggested SI (severity index) method will generate crash black-sites map which
policy makers can use to determine accident-prone zones and take appropriate interventions.
Keywords: GIS, accident-prone zones, severity index, kernel density, road safety.
1. Introduction
Every day over 3400 people die on the
world’s roads and tens of millions of people
are injured or disabled every year. Road
traffic crashes claim more than 1.2 million
lives each year and have a huge effect on
health and development. In addition to
deaths on the roads, up to 50 million
people suffer nonfatal injuries each year
as a result of road trauma, while there are
additional indirect health consequences
that are associated with this epidemic. Road
traffic injuries are currently estimated to be
the ninth leading cause of death globally,
and are predicted to become the seventh
1
Corresponding author: shahriar.rahimi@mail.um.ac.ir
368
leading cause of death by 2030. Most of
these deaths are in countries with low
and middle income where rapid economic
growth has been accompanied by increased
motorization and road traffic injuries. Road
accident’s injuries are the leading cause of
death among young people aged between
15 and 29 years, and data suggest that road
traffic deaths and injuries in low and middle
income countries are estimated to cause
economic losses up to 5% of GDP. Globally
an estimated 3% of GDP is lost to deaths
and injuries caused by road crashes. Road
crashes are a leading cause of preventable
death. Despite this substantial – and largely
preventable – human and economic expense,
International Journal for Traffic and Transport Engineering, 2017, 7(3): 368 - 380
action to combat this global challenge has
been insufficient (WHO, 2015).
Iran’s share of road crashes is more critical
than most countries. It has been estimated
that the cost of traffic accidents in Iran was
about 7 percent of the country’s GDP in
2013. According to official reports in Iran
from March 2014 to March 2015 (1 Iranian
year) traffic accidents fatalities was 16872
people, from which 10951 people (64.9% of
the total fatalities) have been killed in nonurban road crashes. Following figure (see
Fig. 1) shows accident fatalities per province
in Iran from March 2014 to March 2015 (1
year period) )RMTO, 2015(.
Fig. 1.
Crash Counts in Provinces of Iran Based on the Road’s Type
Source:(RMTO, 2015)
One of the most important problems that
traffic officials face is where and how to
implement precautionary measures and
provisions so that they can have the most
signif icant feedback for traff ic safet y
(Erdogan et al., 2008). Site rank ing is
essential in designing engineering programs
to improve safety of a road network. The
sites with potential for safety treatments
are also known as sites with promise, crash
black-sites or hotspots (Huang et al., 2009;
Sorensen and Elvik, 2007).
By identifying road crash black-sites, using
Geographical Information Systems (GIS)
and appending value added data, a more
potent understanding can be gained, with
regards to indicators of casual effects. GIS
is a technology for modeling, processing and
managing land base and related information
(Longley et al., 2005). After identification
of incident black-sites, vital improvements
could be applied to the selected areas with
limited highway budgets. This improves
road safety and ensures cost effectiveness
in resource allocation.
Crash data are usually prov ided w ith
classification according to the collision types
(e.g. rear-end; head-on) or severities (e.g.
slight or serious injury and fatal ) (Wang
et al., 2011). It is particularly important to
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Shad R. et al. Identification of Road Crash Black-Sites Using Geographical Information System
consider road trauma in site ranking, because
the cost of road crashes could be hugely
different at different levels of severity. This
means that, for instance, a road segment
with higher frequency of fatal accidents may
be considered more hazardous than a road
segment with more serious or slight injury
accidents but, fewer fatal accidents therefore
it is crucial to estimate crash frequency for
each severity category (Hu et al., 2010).
researches considering the same criteria
is provided; and then the methodology
employed in this paper is described. This
includes both accident frequency based on
severity to determine black-sites, introducing
the study area, describing the SI model and
description of statistics used in this paper.
It is then followed by the description of the
modeling results. Discussion is then provided
and finally conclusions are drawn.
Geographic information system (GIS) has
been identified as a system of linking a large
number of various databases. GIS is also a
potential tool for generating maps which
present a clear and immediate impression of
the crash distribution on the road network,
identifying those areas that have incident
concentrations (Alam and Ahsan, 2013).
According to the spatial nature of disparate
databases needed for traffic safety analysis,
the GIS would be a good choice to integrate
them. In order to integrate crash information
w ith other relevant data like roadway
characteristics, GIS provides a platform
to facilitate data integration, analysis and
demonstration of results. (Kumaresan et
al., 2009).
2. Literature Review
The main objective of this paper is to
discuss Kernel Density Estimation (KDE
advantages) and then determine traffic crash
clusters in GIS using this method. Later; an
equation is developed that can consider and
model all severity types of traffic crashes
(Severity Index) based on each accident
severity. Using SI results (Severity Index
equation) each kernel maps for each accident
severity is overlaid in GIS environment in
order to determine crash black-sites in the
study area.
The paper is organized as follows: Firstly
in the next section a summary of pervious
370
Crash black-site analysis has traditionally
focused on road segments or specif ic
junctions Traditional methods of accidentprone zone determination by road experts
have included comparing occurrence count
information at different locations and rating
these areas by crash severity. Only lately
has GIS made a huge impact in road crash
black-site research and it brings with it a
wide range of practical spatial-statistical
techniques to increase the accuracy and
information of black-site detection. Crash
black-sites are often determined by a range
of approaches; however there is no general
method, which is why continued comparison
of techniques is necessary if road crash
black-sites are to be detected in the most
successful way (Anderson, 2007). (Bhalla
et al., 2014) proved that GIS is a proper
tool for analyzing multifaceted nature of
incidents and determined the application
of GIS for developing an efficient database
on road crashes. If such type of database is
developed, an appropriate analysis of crashes
can be undertaken and proper management
strategies can be proposed to reduce the
crash rate. (Rodrigues et al., 2015) introduced
a model for road network classification
based on traffic crashes integrated in a
geographical information system. Also, an
equation was introduced to acquire a road
International Journal for Traffic and Transport Engineering, 2017, 7(3): 368 - 380
safety index through the combination of
the following indicators: severity of crashes
and crash costs. In addition to the road
network classification, the use of the model
allows to evaluate the spatial coverage of
incidents in order to indicate the centrality
and distribution of the areas with the highest
occurrence of road crashes.
(Prasannakumar et al., 2011) w ith the
eva luat ion of spat ia l cha rac ter ist ic s
of the crash data by Moran’s I method
demonstrated that crash datasets, as a
whole, are classified as clustered in nature.
Kernel estimation is able to determine blacksites from huge datasets, hence present an
analytical adequate result. The benefits of
these surface representations specifically
of traffic crashes are that they can provide
a more realistic continuous model of crash
black-sites patterns indicating density
changes which are often difficult to produce
using geographically constrained boundary
based models like the road network. The
major benefit for this specific technique is
indicating the extent of risk of an incident,
defined earlier. Generally in defining a
cluster, the surrounding buffer is ignored
which will basically impose an amount of
exposure to incident for those who enter
it. This amount of exposure would not
be considered employing the clustering
methods (Anderson, 2007). Also (Çela et
al., 2013) used the Network Kernel function
to determine whether or not there was a
tendency towards clustering in the whole
crash dispersion. In addition to approving
the patterns of the number of crashes, the
Network Kernel function was used to find
where the concentrations were actually
created. Spatial clusters can be additionally
used for pattern discovery in Geographical
Information System (Turton and Openshaw,
2001). (Pino-Díaz et al., 2012) developed a
f lexible procedure to evaluate proximity
in terms of both time and space of the
happening of crashes. On dense networks
with dispersed traffic, 2D clustering methods
based only on proximity function better
than linear techniques. Edge effects are
restricted to the boundary of the study area
(Steenberghen et al., 2004). Some critiques
of KDE dispute the fact that it considers
discrete phenomenon as a continuous area.
However this paper is also concerned with
the extent of risk in an area (the risk of
crash occurrence). Geographically crashes
will happen over a given surface not just
at a single point because crash reasons can
be traced to the whole effective area. KDE
provides an approach which considers this
concept of extent of crash risk. However one
major disadvantage resumes, which relates to
indicating the statistical importance of the
resulting concentrations (Anderson, 2009).
3. Methodology
3.1. Kernel Density in GIS
T he use of GIS env i ron ment for t he
identification of crash ‘black-sites’ includes:
1- the implementation of crash locations on a
map and 2- the determination of statistically
significant spatial concentrations of crashes.
There are numerous spatial tools developed
to enhance the perception of the changing
geographies of point patterns to determine
accident-prone zones or black-sites. The most
reassuring of these methods is kernel density
estimation (Chainey and Ratcliffe, 2005).
There are many benefits to kernel density
estimation (KDE) as opposed to statistical
and clustering means such as K-techniques.
The main benefit for this function lies in
defining the extent of risk of a crash. The
extent of risk can be described as the surface
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Shad R. et al. Identification of Road Crash Black-Sites Using Geographical Information System
around a specified accumulation in which
there is an increased probability for an event
to happen according to spatial dependency.
On the other hand, by using kernel density
function, a desired spatial unit of analysis
can be determined and be homogenous for
the whole surface which makes comparison
and finally classification possible. Kernel
density estimation procedure includes
placing a symmetrical area over each point
and then calculating the distance from the
point to a reference location based on a
mathematical function and then summing
the value for all the areas, including those at
which no accidents of the indicator variable
were recorded, for that certain location. This
process is repeated for successive points (Sun
et al., 2012). Hence this process grants the
ability to place a kernel over each event, and
the sum of these individual kernels gives the
density estimate for the distribution of road
crashes (Fotheringham et al., 2000).
The impact of placing these kernels or
humps over the incidents is to produce a
continuous and smooth area (Potoglou,
2008). Density can be measured by two
methods; simple and kernel (Anderson,
2009). Kernel density estimation method,
applied to point distribution on a plane, is
the Network Kernel Method that calculates
the density in a linear unit which estimates
the density points on a network based on
formula (Fotheringham et al., 2000):
(1)
where f (x, y) is the density estimate at the
location (x, y); n is the number of incidents,
h is the kernel size or bandwidth, K is the
kernel function, and di is the distance
between the location (x, y) and the location
of the ith incident.
The kernel approach separates the whole
research area into specified number of
cells. The kernel method draws a circular
neighborhood around each feature point
(accidents), instead of contemplating a
circular neighborhood around each cell like
the simple method. Then a mathematical
equation is used that goes from 1 at the
position of the feature point to 0 at the
neighborhood boundary (see Fig. 2).
Fig. 2.
Sketch of Kernel Density Method which is Employed in GIS Processing for this Research
Source:(Bailey and Gatrell, 1995)
372
International Journal for Traffic and Transport Engineering, 2017, 7(3): 368 - 380
This process calculates the densit y of
incident points around each output grid
cell. The density (D) of a cell is determined
as the value (number of accidents (n)
multiplied by weight) of crashes per unit
area.
In this paper after a number of tests using
Point Density in Spatial Analyst Tools in
GIS environment, bandwidth of 500 m and
cell size of 1 km were selected.
3.2. Structure
As it can be seen in Fig. 3 the process of
this research is summarized in a flowchart
to provide a better understanding of data,
process, and objectives of this paper.
Fig. 3.
Study Flowchart
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Shad R. et al. Identification of Road Crash Black-Sites Using Geographical Information System
3.3. Severity Index Model
(2)
Since the crash severity is categorized in
nature (ranging from non-injury or property
damage to fatal), it appears essential to
choose discrete ordered response models
for evaluating crash severity data. Samples
of previous researches employing ordered
response models include (Eluru et al., 2008;
Quddus et al., 2009). Crash data for Khorasan
Razavi province of Iran from police reports
were collected and included in the GIS
database from March 2010 to March 2015 (5
year) based on accident counts and severity
in 3 category (Fatal, Injury & property
damage). DATA considering various types of
injury accidents severities was not available
to include in modeling. There weren’t any
major changes in roads geometrics over the
years. Also roads built after 2010 are excluded
from modeling process. For determining
black-sites in study area, a density function
for each severity level in GIS processing with
the search radius of 500 meter is to be used.
Finally, density maps overlay according to
the following Severity-Index formula (See
Eq. (2)) )Ayati and Vahedi, 2008(:
To consider crash severity in black-sites
identification, three crash severity classes
(property damage, injury, and fatal) are
included in Severity-Index formula (See Eq.
(2)). Each category has its own coefficient
in Eq. (2). Coefficients demonstrate the
impact of each category on the creation
of black-sites. It’s reasonable that as the
severity increases the coefficient should also
increase. Thus, for fatal accidents 16, for
injury accidents 3, and for property damage
accidents 1 is considered as coefficient in
Eq. (2). The road segment with SI over 60
is considered as a black-site. The limit 60 is
indicated according to 1000 meter segment
length, through consulting and field work
suggested by )Ayati and Vahedi, 2008(.
The most vital stage of the research is
detailed registration of crash data. In this
study, 110150 accidents data from March
2010 to March 2015 (3075 Fatal, 31987
Injury & 75088 property damage accidents),
obtained from the Khorasan Razavi province
Police Department is to be used. Accidents
statistics are shown in Table 1.
Table 1
The Number of each Crash Type per Year
5thYear
4th Year
3rdYear
2ndYear
1stYear
Property
damage
12784
14014
14550
14657
19083
Injury
5286
6953
5614
6513
7621
Fatal
534
568
521
682
770
3.4. Study Area
Fig. 1 and Table 1 stress the necessity to
initiate immediate actions for Khorasan
Razavi province with the second rank of
374
fatalities in road accidents in the whole
country. Khorasan Razavi, as one of Iranian
prov inces, is a concentration location
of industrial, tourism and agricultural
activities. Especially, in holidays with
International Journal for Traffic and Transport Engineering, 2017, 7(3): 368 - 380
tourists coming from abroad, traffic density
increases drastically. Mashhad in Khorasan
Razavi province is the second largest and
most populated city of the country. Khorasan
Razavi province has 111 Km of freeways,
1015 Km of expressways, 1240 Km of main
arterial roads and 3960 Km of secondary
arterial roads. 8927 million person-kilometer
travel have been made from/to and 4831
million person-kilometer travel have been
made through the province. 15556 million
Ton-kilometer goods have been delivered
from/to and 8528 million Ton-kilometer
goods have been delivered through the
province. According to statistics in 2015,
with 760 losses of lives in traffic accidents the
state is second in the rank of total accident
rates after Tehran, second in the rank of
mortality rates after Fars, second in the rank
of injuries after Tehran.
T he region has been one of the most
important transport areas with neighbor
countr ies for a long time, thus it has
above average heav y vehicle ratio than
other provinces in Iran which increase
traffic crashes severity. Having a smooth
topography (mostly f lat plains with few
foothill areas) and straight routes enables
high-speed traffic. Thus, in addition road
trauma is inevitable, and the severity of
crashes and losses is at a very disturbing
level. Fig. 4 shows the study area and its
roads on the map and it demonstrates the
concentration of important cities in the
province.
Fig. 4.
Study Area (Khorasan Razavi Province, Iran)
4. Results and Discussion
4.1. Accidents Frequency
Crash data provides a good infrastructure
for the prevention of road trauma. In this
study, accidents location are included in GIS
processing based on coordinates determined
b y GPS de v ic e s , a nd e ac h ac c ident
information provided by police department
reports is imported to GIS process. After
defining all accident locations (In 3 category:
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Shad R. et al. Identification of Road Crash Black-Sites Using Geographical Information System
fatal, injury, and property damage) density
values for each class is calculated with a 500
meter bandwidth for mentioned time period
(5 years) and study area (Khorasan Razavi
province) based on the kernel function (see
Fig. 5).
Fig. 5.
Crash Density Maps
Fig. 5 indicates the density values for each
category in the processing extent (Study
area). Fig. 5. A,B,C, respectively, shows
density for property damage, injury, and
fatal accidents. Fig. 5.A shows nearby cities
the number of non-injury crashes increases
dramatically because closer to cities traffic
increases and thus the probabilit y of
incident. Also, uncontrolled road exits and
entrances, uncontrolled roadside access,
and pedestrians on the road, are another
reasons for property damage crashes increase
376
around cities. Fig. 5.B indicates most Injury
crashes occur at a distance of approximately
20_25 kilometer from the city because
there is a concentration of factories in these
distances and uncontrolled intersections and
highway exits are additional reasons. Fig. 5.C
demonstrates most fatal accidents occur at a
distance of approximately 30 kilometer from
the city mostly because of driver fatigue,
higher speed, getting closer to urban area,
and uncontrolled access to farm properties
around the road.
International Journal for Traffic and Transport Engineering, 2017, 7(3): 368 - 380
(Rodrigues et al., 2015) showed it is possible
to categorize segments of the road network
according to levels of road safety based on
crash Severity Indexes and to implement a
broad set of evaluation over a large study
area. Also, this approach can be applied to
approve the planning of counter measures
intended to improve road safety of a certain
area considering economic restraints. As
mentioned above, this paper concludes the
same results, that kernel density estimation
is an appropriate tool to model crashes in
Geographical Information System. Mainly
because not only it determine accidents
clusters in road network but also indicates
accidents risks in surrounding areas. This
can be employed in policy mak ing for
creating safer road side for pedestrians or
businesses alongside the road.
4.1. Black-sites Determination
Identification of black-sites is a process to
detect high density crash locations within the
road network. However, for practical reasons
the black-site definition is stated very simply.
Crash black-site evaluation intends to help
the determination of areas with unusual
high concentration of crash occurrence.
There is a wide range of data in the previous
researches as to what a crash black-site is and
how it is identified or predicted spatially and
numerically. According to (Hauer, 1996)
some researchers use crash occurrence
frequency, some rank areas by crash rate
while others use a combination of these
two. Nevertheless, the most commonly used
approach to indicate whether a location has
a safety problem is based on the road crash
history and determination of the “blacksite”. Also, the whole crash prevention
procedure is often referred to black-sites
improvement. In this paper, to consider
both frequency and severity of collisions in
black-sites determination, accident density
maps in each category is overlaid within
GIS process using Severity-Index formula
(Eq. (2)).
Fig. 6.
Severity-Index
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Shad R. et al. Identification of Road Crash Black-Sites Using Geographical Information System
Fig. 6 demonstrates crashes black-sites
(red zones in the map) calculated based on
Severity-Index formula (Eq. (2)). Red zones
(known as very high risk) in Fig. 6 indicate
black-sites or areas where SI exceeds the
upper limit of 60. Yellow areas indicate high
risk zones where SI -index is approximately
45-60. Green areas or medium risk zones
are where SI-index is approximately 3045. White areas show zones with low risk
of road crash (Severity-index is below 20).
The reason that there is no risk free area
in the map is, that travel is an inherently
risky activity, because movement creates
kinetic energy, and if there is an accident
and collision, the energy exchange can be
damaging to both humans and property.
As it can be seen in Fig. 5 most black-sites
are within the distance of 20-30 kilometer
of cities. There various reasons for this
concentration of black-sites in the entrance
of cities. Most important reasons are that
these areas have many uncontrolled access,
intersections, and crossroads for farms,
factories, villages, and small cities. The other
reasons for accidents in these black-sites
are usually based on human errors, mostly
because of driver’s weariness. To determine
driver’s fatigue, a series of emotive phrases
such as: “we are almost there” and “just a
little bit further” are usually deemed.
From the data evaluated in (Alam and Ahsan,
2013), the most hazardous area identified is a
2.7 kilometer long segment which was from
11.0 kilometer to 13.7 kilometer from city’s
midpoint. At the starting of this segment
of the road there was a petrol pump and at
the end of the segment a spinning mill was
found. In a city’s road network with high
density traffic, crash locations are generally
based on prox i m it y aspects. I n t hese
environments, 2D clusters may propose causal
relationships. A sample is the detection of
378
crash concentrations near access roads. These
indications are very similar to this paper
results as discussed above. The majority of
these determined black-sites were cross roads
for villages and small cities. The first urgent
measure for these locations is to increase
traffic road signalization and then to make
safe intersection arrangements or increasing
the number of lanes within the road segment.
5. Conclusions
T he issue of ran k ing potentia l crash
locations or detecting black-sites is perhaps
a difficult problem. From the policy making
point of view, a solution to this issue can
have a substantial impact on society, not
only because it can reduce the crashes on
a particular site but, at the same time, it
can prevent budgets to be allocated to the
wrong locations. With a proper set up of a
GIS, traffic agencies can retrieve, analyze
and demonstrate crash data and spatial
attributes of this data. This system has a lot
of benefits such as quick access for gathering
information, data storage, integrity, and
output. Using the Geographical Information
System (GIS) is useful in displaying of the
crash locations on the map. At the same time,
because of the loss of lives and the loss of
large amount of resources, the researches
aiming to prevent the traffic accidents are
very popular in developing countries. In this
situation, it is very important to forecast the
probability of the occurrence of accidents.
Traffic accident analysis is a very complex
topic due to existence of many factors
affecting accidents spatially. Traffic accident
reports must be more detailed and formatted
properly for spatial and statistical analysis.
This paper presents a methodolog y to
identify high density crash black-sites and
in turn create a clustering technique which
International Journal for Traffic and Transport Engineering, 2017, 7(3): 368 - 380
determines casual indicators more likely to
be present at certain clusters, therefore being
able to compare across time and space. The
kernel density estimation method enabled an
overarching visualization and manipulation
of the accidents based on density which was
used in turn to create the basic spatial unit
for the black-site clustering method. The
classification of road accident black-sites in
road safety, still remains an important and
yet under developed theme.
Anderson, T.K. 2009. Kernel density estimation and
K-means clustering to profile road accident hotspots,
Accident Analysis & Prevention 41(3): 359-364.
Results of this paper conclude that exploring
and tak ing advantage of a GIS toolset
revealed to be a valuable tool to define and
validate the proposed model. On one hand,
it was possible to classify segments of the
road network in accordance with levels
of road safety based on accident Severity
Indexes and to apply a large set of analysis
over a wide study area. On the other hand
Kernel Density Estimation tool in GIS
offers a method which takes into account
the spread of accident risk. Therefore, KDE
is an appropriate method to model accidents.
Also GIS is capable of overlaying models of
accidents with different severity based in
their given coefficient. Final determined
traffic accidents black-sites on non urban
areas indicated that these places were usually
uncontrolled road sides, intersections, and
crossroads located within the distance of
20-30 kilometer of city’s centers.
Bhalla, P.; Tripathi, S.; Palria, S. 2014. Road Traffic
Accident Analysis of Ajmer City Using Remote Sensing
and GIS Technology. In Proceedings of the International
Archives of Photogrammetry, Remote Sensing and Spatial
Information Sciences, 40(8): 1455-1462.
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