Accident Study
Er. Romharsh Oli
Lecturer
Everest Engineering College
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Accident Study
• The problem of road accident is ever-existing and acute in
highway transportation due to complex flow of vehicular
traffic, presence of mixed traffic and pedestrians.
• Consequence of traffic accident may include property
damages, personal injuries, fatal cases as well as social
and moral effect of a community.
• Systematic studies to investigate the causes of accidents
and preventive measures in terms of designs and control
may decrease the rate of accidents.
• The cost of the traffic accident helps to evaluate an
improvement scheme for reducing accidents.
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Accident Study
• Traffic safety is most important issue in the present
context of motorization.
• More than 1.3 million people are killed in the world only
by the road accidents each year and 50 million people
injured and disabled as the result (WHO).
• This is number one cause of death for young (below 25
years) people worldwide.
• In Nepal there were 166 deaths due to road accident
2077/78 out of 9545 accidents.
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Source: https://www.roadsafetyfacility.org/country/nepal.
Sited 7-4-2022
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Definitions:
• Road accident: An accident (collision, overturning or
slipping) which occurred or originated on a road open to
public traffic resulting in either injury or loss of life, or
damage to property, in which at least one moving vehicle
was involved.
• Person killed: (given in the Convention of Road Traffic
(Vienna, 1968) “Any person who was killed outright or who
died within 30 days as a result of the accident.”
• Fatal accident: an accident in which one or more person
were killed.
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International comparison of road accidents:
• It is important to compare the road safety situations in
different countries.
• The data vary in different countries due to economic
conditions, education and literacy, climate, types of
vehicles, traffic conditions, population and vehicle
density, and others.
• Most countries maintain records and statistics about
road safety and accidents.
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Prime causes of accidents
Prime causes of Road accidents Percentage of accidents
Human factors alone
65
Human + Road
25
Human + Vehicle
5
Road factors alone
2
Vehicle factors alone
2
Human + Road + Vehicle
1
Total 100 13
Objective of Accident Study
• To study the causes of accidents and to suggest corrective
treatment at potential locations.
• To evaluate performance of existing facilities in terms of
safety
• To support proposed design. (Road Safety Audit)
• To carry out before and after studies of improvement
schemes.
• To make computations of financial loss during accidents.
• To give economic justification for improvement schemes.
• To define and identify high-accident locations.
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Causes
• Drivers
– Excessive speed, carelessness, violation of rules and regulations, fatigue, sleep, alcoholic
etc.
• Pedestrians:
– Violating regulations, carelessness.
• Passengers:
– Alighting from or getting into moving vehicles.
• Vehicle defects:
– Failure of brakes, steering system, lighting system, tyre burst, etc.
• Road condition:
– Slippery or skidding road surface, pot holes and other damaged conditions.
• Road design:
– Defective geometric design.
• Weather:
– Fog, snow, rainfall, dust, smoke etc which restrict the normal visibility.
• Animals:
– Stray domestic animal and wild animals.
• Other causes:
– Incorrect signs or signals, advertisement boards, service stations etc.
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Collection of Accident data
• Collection of accident data is the first step in accident
study. Data collection helps to identify the causes of
accident and suggest appropriate remedial measures.
• The details to be collected are briefly mentioned as
follows:
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• General:
– Date, time, persons involved in the accident, classification of accident
(fatal, serious, minor etc.)
• Location:
– Description and details of the location site of accident.
• Details of vehicles involved:
– Registration number, description of vehicle, loading details, vehicles
details, vehicular defects etc.
• Nature of accident:
– Condition of vehicles, details of collisions, pedestrians or objects involved
damages etc.
• Road and traffic conditions:
– Details of road geometry, surface characteristics, traffic condition (density
etc.)
• Primary causes of accident:
– Various possible cause and primary causes.
• Accident costs:
– Property damages, personal injuries and causalities. 17
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“Before and After” accident analysis
• When an accident problem has been identified, and an
improvement implemented, the engineer must evaluate
whether or not the remediation has been effective in
reducing the number of accidents and/or fatalities.
• A “before and after” analysis must be conducted. The
length of time considered “before and after” the
improvement must be long enough to observe changes in
accident occurrence.
• For most locations, periods ranging from three months to
one year are used. The length of the “before” period and
the “after” period must be the same
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• The normal approximation test is often used to make
this determination. The statistics Z is computed as:
test statistic representing the reduction in accident on the
standard normal distribution
The normal distribution table is entered with this value to find the
probability of Z being equal to or less than Z1. If prob [Z ≤ Z1 ] ≥ 0.95,
the observed reduction in accidents is statistically significant.
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Site Analysis
• One of the most important tasks in traffic safety is the
study and analysis of site-specific accident information
to identify contributing causes and develop site
remediation measures that will lead to improved safety.
• Once location has been statistically identified as “high-
accident” location, detailed information is required in
two principal ways:
– Occurrence of accident
– Environmental and physical conditions
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• Occurrence of accident: The best information on the
occurrence of accidents is compiled by reviewing all
accident reports for a given location over a specified
study period. This can be done using accident record.
• Environmental and physical conditions: are
established by a through site investigation.
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Measures for the reduction in accident rates
• The various measures to decrease the accident rates
may be divided into three groups:
– Engineering
– Enforcement “3-Es”
– Education
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Engineering Measures
• Road design:
– The geometric design features: sight distances, width of pavement,
horizontal and vertical alignment and intersection design elements
are checked and corrected if necessary.
– The pavement surface characteristics: are checked and suitable
maintenance steps taken to bring them up to the design standards.
• Preventive maintenance of vehicle:
– The braking system, steering and lighting arrangements on vehicle
may be checked.
• Before and after studies:
– After making the necessary improvement in design and enforcing
regulation, it is again collect and maintain the record of accidents
“before and after” the introduction of preventive measures to study
their efficiency.
• Road lighting:
– Lighting is particularly desirable at intersections, bridge sites and at
places where there are restrictions to traffic movements.
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Enforcement measures
• Speed control:
– Checking of spot speed of all fast moving vehicles should be done at
selected locations and timings and legal actions on those who violate the
speed limits should be taken
• Traffic control devices:
– Signals may be re-designed or signal system be introduce if necessary.
Proper traffic control device like signs, markings or channelizing island may
be installed if necessary.
• Training and supervision:
– the transport authorities should be strict in testing and issuing license to
driver.
• Medical check:
– The drivers should be tested for vision and reaction time at prescribed
intervals.
• Special precautions for commercial vehicles:
– having attendant to help and give proper direction to drivers of heavy
vehicles.
• Observance of law and regulations:
– Traffic authorities should send study groups of trained personal, to different
locations to check whether the traffic regulations are being followed by the
road users and also to enforce the essential regulations. 26
3. Educational measures
• Education of road users:
– The passengers and pedestrians should be taught the rules
of the road, correct manner of crossing etc.
• Safety drive:
– Imposing traffic safety week when the road users are
properly directed by the help of traffic police and transport
staff is a common means of training the public these days.
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