infrastructures

Article
Influence of Road Infrastructure Design over the Traffic
Accidents: A Simulated Case Study
Dorin-Ion Dumitrascu

Department of Automotive and Transport Engineering, Transilvania University of Brasov, 1 Politehnicii,

500036 Brasov, Romania; d.dumitrascu@unitbv.ro

Abstract: The influence of road infrastructure over the severity of road accidents, in particular some
specific features of it, represents the subject of this study. Generally, when an accident occurs, its
causes are represented by a number of factors such as driver experience, fatigue, driving under
the influence of alcohol and other psychoactive substances, road configuration, weather conditions,
speeding, distracted driving, and unsafe road infrastructure. Road design is a key factor regarding
the safety of all traffic participants. In this paper, the influence of unsafe roadside element designs on
the incidence of traffic accidents, the degree of vehicle passenger injury, and the level of car damage
were investigated. The present study was inspired by the high number of accidents produced on
European route E68 (DN1) in Romania, a significant part of which was generated and accentuated by
the effects of improper roadside design.

Keywords: road infrastructure; accident; forgiving or unforgiving roadside; safety; ditch; accident
simulation

1. Introduction
Road accidents and their causes and effects represent a major problem for any country
from a medical, social, and economic point of view. In this context, identifying and
understanding the complex factors that affect road accidents represent an essential research
Citation: Dumitrascu, D.-I. Influence
field for road safety.
of Road Infrastructure Design over
Therefore, the need to improve road safety must be a mandatory objective for trans-
the Traffic Accidents: A Simulated
port authorities, which can be met through certain strategies, such as new or improved
Case Study. Infrastructures 2024, 9, 154.
infrastructure, tougher legislation, traffic participant education, etc. The sooner strategies
https://doi.org/10.3390/
infrastructures9090154
are used to intervene on the contributing factors of road accidents, the more visible the
preventive effect will be.
Academic Editors: Alessia Ruggeri All these aspects must be included in a safety system approach [1] based on suitable
and Orazio Pellegrino procedures, methods, and policies in order to develop and improve road safety. The interest
Received: 4 August 2024 for studying factors affecting road safety—the effects of road and traffic characteristics—
Revised: 2 September 2024 represents a dynamic field in continuous evolution.
Accepted: 3 September 2024 The European Road Safety Observatory (ERSO) provides reliable and comparable
Published: 9 September 2024 data about road accidents, detailed information and analysis about road safety trends,
and procedures and policies in the European Union (EU). Considering the ERSO annual
report, the 2023 report reveals stalling progress in reducing road fatalities in too many
countries [2]. Despite this, reducing traffic accidents and their fatalities and improving road
Copyright: © 2024 by the author. safety represent a continuous concern for the EU.
Licensee MDPI, Basel, Switzerland. In this regard, the European Commission [3] set a target for 2030 to halve the number of
This article is an open access article serious injuries in the EU, considering 2020 as a landmark, and set an ambitious objective of
distributed under the terms and
minimizing towards zero fatalities in the long term for the year 2050, termed “Vision Zero”.
conditions of the Creative Commons
This goal aligns with the United Nations resolution [4], which declared the period
Attribution (CC BY) license (https://
2021–2030 as the Decade of Action for Road Safety, with the target of preventing at least
creativecommons.org/licenses/by/
50% of all road traffic injuries and fatalities by 2030.
4.0/).

Infrastructures 2024, 9, 154. https://doi.org/10.3390/infrastructures9090154 https://www.mdpi.com/journal/infrastructures

Infrastructures 2024, 9, 154 2 of 22

Going back to the ERSO report, it also reveals that Romania is characterized by one
of the highest incidence of road accidents in the EU. Ref. [5] reveals that among the most
common causes are excessive or inappropriate speeds, especially in bad weather conditions.
In Romania, most road accidents take place on national roads, but it is important to mention
that the most frequent fatal accidents take place on highways. Over 30% of the serious
accidents that have occurred have been on national roads. It must be admitted that it is not
only an infrastructure problem but also includes the fact that the accidents were caused
by people.
The year 2022 represents the starting point of the National Road Safety Strategy
implementation for the period of 2022–2030. The main directions of action stipulated by it
are a high-performance management of road safety, safer conditions for the use of roads,
increased security conditions for the infrastructure, and prevention and monitoring, as well
as optimal interventions in cases of emergency situations [5].
In order to achieve similar goals, [1] foresees the implementation of a Safe Systems
procedure for road safety, based on the following main elements:
• Human behavior—considering that no matter how well people are trained for respon-
sible road use, they can make mistakes, and road infrastructure must be developed
while taking this aspect into account.
• Human frailty—consisting of the limited resistance of the human body to various
types of collisions and mechanical stress, the assessment of the injury risk, and the
severity of injuries. It represents another design criterion.
• Forgiving systems—meaning that any human error must not be potentiated by the
road, correlating with vehicle type and interaction with other traffic participants.
The forgiving roads concept [6] assumes the minimization of driving error conse-
quences, rather than preventing them, and this is mainly because of the human factor,
which can be estimated.
Having this principle as a guideline, the entire road infrastructure must comply with
the following:
• Minimize the risk of vehicles leaving the carriageway by using vehicle active systems
(e.g., line assist), correlated with appropriate road delineation.
• Provide an adequate stopping distance or recovery area when a car runs off the road.
If a collision still occurs with any roadside obstacles, it is mandatory that impact forces
transmitted to the vehicle occupants be kept at minor levels (i.e., no fatal or serious injury
outcomes). According to [7,8], the main approaches for studying road safety are repre-
sented by infrastructure characteristics (e.g., road type and configuration and investment
levels), the environment (e.g., road geometrical design and weather conditions), and traffic
conditions (e.g., vehicle types and traffic volume). These elements are critically related
because proper road infrastructure will have a beneficial impact on the number and severity
of accidents. Any other contradictory assumptions can be considered subjective, being
dependent on drivers’ experience and education.
An important aspect in the context of infrastructure sustainable development is to
identify the risk factors related to it and their impact on road safety. It becomes obvious that
such an in-depth analysis is specific to every EU country, for all road types, considering
aspects such as road infrastructure design, environmental factors, and traffic volume
and control.
Contributing factors to road accidents can be grouped as follows [7]: human factors
(e.g., experience, fatigue, distracted driving, speeding, risky overtaking, and the influence of
alcohol and/or psychoactive substances), road infrastructure factors (e.g., road type, surface
type, road segment configuration—alignment, curve, tunnels, and junctions—and road side
configuration), traffic factors (e.g., vehicle mix and density—congestion), environment and
weather (e.g., winding road, fog, rain, frost, and snow), and vehicle design and physical
conditions (e.g., safety systems, suspension condition, and tire wear).
Infrastructures 2024, 9, 154 3 of 22

In the above classification of road accident favoring factors it is mandatory to include

weather conditions too, because in many circumstances they represent an aggravating factor
in the frequency of accident occurrence [9,10] (accident risks are significantly higher during
bad weather conditions). The meteorological phenomena type (e.g., rainfall intensity, fog,
snow, etc.) is another element that must be considered during the road infrastructure design
process, as well from the perspective of the forgiving roads concept [1]. Adverse weather
conditions influence a driver’s visibility (driver’s standard reaction time is extended),
reduce the friction coefficient between tires and carriageway, extend the stopping distance,
while in the worst-case scenario they will determine the skidding and aquaplaning of
the vehicle.
From the above analyses regarding the factors favoring the occurrence of accidents,
having in mind [6], it becomes obvious that in addition to the human factor, any road
infrastructure improvement can either prevent or, in the most pessimistic scenario, reduce
the effects of human errors. So, a proper road system design can prevent human errors
and this will be materialized in less traffic accidents. Ref. [6] considers three principles in
order to prevent human errors during driving: keeping away from an unintended road use;
avoiding considerable differences in direction, mass, and speed; preventing unpredictability
amongst road users.
Passing from human error prevention to accident occurrence and injury severity,
in [11] they are explained through the engineering system and human behavior as linked
factors that represent two major elements of risk. An engineering solution can increase
traffic safety, but at the same time it must not influence the driver’s alertness. Road safety
engineering and human behavioral adaptation represent key elements in reducing the
number of accidents. In this regard [12] considers that road infrastructure design must be
done in such a way as to ensure optimal driver behavior in terms of speed, anticipation,
and attention. Situations as incorrect visibility of the carriageway, poor anticipation of road
curves combined with inadequate speed, poor quality of tires or excessive wear of them,
accentuated by unfavorable weather conditions (e.g., rainfall) can favor the occurrence
of accidents.
The safe roads concept, in particular self-explaining roads [13], involves an under-
standable one from the driver’s point of view, considering several important specific
elements, such as: roadway quality in terms of adhesion and bump free asphalt surface,
day and night visibility, predictable road regardless of weather conditions, road markings
and traffic signs, road sector optimal geometric configuration, etc. On the other hand, a
high density of road signs or markings in a complex traffic scenario, according to [14], may
lead to an overload of information and an increased risk of driving errors. An optimal
practical combination of those elements is able to level up driver confidence, anticipation,
and attention, influencing his reaction time, both for safe driving and to avoid certain
dangerous situations within reasonable limits.
Considering all the above presented aspects, by evaluating the dependence between
infrastructure features and drivers’ behavior, including limit situations, it is possible to
decrease or suppress traffic accidents, especially those generated by the faulty design of
road infrastructure.
Therefor it is mandatory to analyze accident causes and develop efficient counter-
measures to eliminate these causes, by carrying out professional road safety analyses with
appropriate implemented measures.
One of these measures refers to the introduction of consistency rules [6,15] in road
design process. Design consistency refers to road geometry conformity with driver ex-
pectancy, generating predictability. Theoretically, drivers make fewer errors at geometric
features that correspond to their expectations. An inconsistency in road design represents a
geometric feature or a feature mix with unusual characteristics that drivers may approach
in an unsafe manner. Such situations could lead to speed errors, inappropriate driving
maneuvers, and finally to accidents. Their effects can be aggravated by inadequate roadside
design, a fact which will be detailed in the following section.
 Infrastructures 2024, 9, x FOR PEER REVIEW 4 of 23

Infrastructures 2024, 9, 154 4 of 22

maneuvers, and finally to accidents. Their effects can be aggravated by inadequate road-
side design, a fact which will be detailed in the following section.
2. The Study Scope
2. The Study Scope
The paper’s goal was to investigate the effect of the unforgiving roadsides on European
The paper’s goal was to investigate the effect of the unforgiving roadsides on Euro-
route E68 (DN1) in Romania, over the degree of vehicle passenger injury, respectively, the
pean route E68 (DN1) in Romania, over the degree of vehicle passenger injury, respec-
level of car
tively, thedamage,
level of car anddamage,
having and as ahaving
base point
as a basespecific
pointaccidents produced
specific accidents on the road
produced on
sector between the cities of Bras , ov and Făgăras , , in
the road sector between the cities of Brașov and Făgăraș, in Brașov county. Bras , ov county.
Also, thethe
Also, work work aimed
aimed totoreconstruct
reconstructthrough
throughsoftware
softwaresimulation
simulation the probable mech-
the probable mecha-
nism of the occurrence of such
anism of the occurrence of such accidents. accidents.
TheTheE68E68(DN1)(DN1) is is
oneone ofofthe thelongest
longestand andmost mostusedused roads
roads in Romania,permanently
in Romania, permanently
recording
recording high
hightraffic values.
traffic values. The Theanalyzed
analyzed sector
sectorisisa adifficult
difficultoneonebecause
becauseof ofits
itsconfigura-
configu-
tion, and in
ration, andaddition
in addition the road
the road sector is characterized
sector is characterized by by a high rate
a high ofof
rate accidents.
accidents.
In the current
In the current study
study continuous
continuoushazards hazardsare are addressed,
addressed, and and the
theditches
ditchesininparticular,
particular,
which
whichgenerally
generally areareparallel
parallel to the roadway.
to the roadway. TheThe analyzed
analyzed accidents
accidentswere
were caused
caused by by
vehicle
ve-
run-off
hicleinto ditches
run-off as can be
into ditches as seen
can be inseen
Figure 1.
in Figure 1.
SomeSome relevant
relevant crashes
crashesare areillustrated
illustratedwhichwhichoccurred
occurred on the E68 E68 (DN1)
(DN1)in inRomania
Romania
on on
thethespecified road sector. As can be seen
specified road sector. As can be seen in the photos, inin the photos, in most of the cases the impact
of the cases the impact
between
between vehicle
vehicle andand ditch
ditchcauses
causesthe thecarcartotooverturn
overturn or or roll
roll over. In
In this
this scenario,
scenario,apart
apart
from
from thethe material
material damage,
damage, it itisisalso
alsovery
veryimportant
important to to evaluate
evaluate thethe accident
accidenteffect
effectononthe
the
vehicle
vehicle occupants.
occupants.
TheThe photos
photos reveal
reveal thatininmost
that mostofofthethecases
casesthe thevehicle–ditch
vehicle–ditch accidents
accidentsoccurred
occurredinin
adverse
adverse weather
weather conditions
conditions (wetroad
(wet roadsurface),
surface),aafact fact that
that indicates
indicates prior
priorvehicle
vehicleskidding,
skidding,
most
most likely
likely induced
induced bybyspeeding
speedingororby byaasudden
sudden steering
steering maneuver
maneuverdue duetotopoor
poorunder-
under-
standing
standing of of
that that road
road section.Also,
section. Also,somesomephotos
photos show show thatthat the
the intervention
interventionofofmedical
medical
andand extrication
extrication crews
crews at at
thethe sceneofofthe
scene theaccidents
accidents was was necessary,
necessary, this
this fact
factrepresenting
representinganan
indicator of the crash
indicator of the crash severity. severity.

(a)

Figure 1. Cont.
Infrastructures
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2024,2024, 5 of 2322
5 of

(b)

(c)

Figure 1. Cont.
Infrastructures 2024, 9,2024,
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of 23
22

(d)

(e)
Figure 1. Examples of accidents with hazardous roadside ditches—(a) to (e) vehicles over-
Figure 1. Examples
turning, of accidents
rollover [16]. with hazardous
In the presented roadside
context two factors ditches—(a–e)
accumulate: firstvehicles
a human overturning,
error, then
rollover [16]. In the
accentuated presented
by an context
unforgiving two factors
roadside, accumulate:
a ditch. first abecomes
Thus, the study human relevant
error, then
by accentuated
establishing
by antheunforgiving roadside,
probable collision a ditch. Thus,
dynamics, the study
respectively, becomes
through relevant
analyzing itsby establishing
effect the probable
on the vehicle’s occu-
pants.
collision More than
dynamics, this, some forgiving
respectively, through measures
analyzingareits necessary to be
effect on the implemented
vehicle’s in order
occupants. to com-
More than
this, pensate such human
some forgiving errors,are
measures bynecessary
reducing or
to eliminating its effects.
be implemented in order to compensate such human
errors, by reducing or eliminating its effects.
3. The Study Background
3. The Study Background
Generally, as it was mentioned before, there are a multitude of factors that can gen-
erate road accidents,
Generally, related to the
as it was mentioned following:
before, traffic
there are volume, road
a multitude type and
of factors thatits configura-
can generate
tion , weather conditions, environment, and all categories of road users.
road accidents, related to the following: traffic volume, road type and its configuration, In this regard,
traffic characteristics (such as speed, density), insufficient driving skills,
weather conditions, environment, and all categories of road users. In this regard, traffic and road ele-
ments (such as geometry, quality and condition of the asphalt surface, roadsides
characteristics (such as speed, density), insufficient driving skills, and road elements (such design)
can favor quality
as geometry, the occurrence of road of
and condition accidents.
the asphalt surface, roadsides design) can favor the
occurrence of road accidents.
Infrastructures 2024, 9, 154 7 of 22

National roads in Romania, due to their multiple characteristics, constantly represent

the category where a large number of serious road accidents occur, characterized by high
values of injury and fatalities, speed being an important generating factor. Statistics show
that 20% of serious traffic accidents in Romania are caused by speeding.
Several studies [17–21] analyzed the dependence between speed and accident fre-
quency (accident rate), considering that increased speed causes more accidents. Certain
drivers that are speeding, in limit situations, do not know how to manage them, or the
reaction time combined with an avoidance maneuver does not allow them to avoid the
accidents. In particular, a higher speed will also increase the total stopping distance of
the vehicle while the probability of accident occurrence is also higher, especially in wet
conditions (slippery road, poor visibility, different friction coefficients on tires, etc.). Thus,
by reducing the speed, a decrease in accident rate can be obtained.
On the other hand, speed cannot be seen as a stand-alone factor of accident occurrence,
and with the speeding theory it is necessary to include other mixed elements such as the
following: variations, road-tire interaction, driver experience, weather conditions, visibility,
sudden trajectory change, erroneous estimation of a curve radius, etc.
Another major element in the safety field is the road itself. Its main design character-
istics (e.g., geometry, alignment, curves, junctions, and all other infrastructure elements,
including roadsides) could play an important role in improving traffic safety. For example,
an increased number of curves on a certain road sector can increase the possibility of
accident occurrence. This fact can be accentuated by the adverse weather conditions and
drivers’ lack of experience in managing the relevant road section. Depending on the partic-
ularities of the road sector, the type of accident, and the traffic conditions, only material
damages can result, but in certain situations the occupant injuries can also occur. Herein,
the improper design of road infrastructure can affect in a negative manner the road safety.
According to [14] a significant percentage of fatal road accidents in the EU are single-
vehicle type accidents, classified as run-off-road accidents (vehicle leaves the carriageway
and crashes to the roadside).
Roadside hazards can be grouped as follows [1,14]:
• Single fixed obstacles (e.g., trees, vegetation, utility poles, road signs, safety barrier
terminations, rocks, drainage features, etc.);
• Continuous hazards (e.g., ditches, slopes, road restraint systems, curbs, etc.);
• Dynamic roadside hazards (e.g., pedestrian and bicycle facilities, parking).
In Romania, the special characteristics of the road (e.g., curve, tunnel, bridge, inter-
sections, railway crossing, etc.) can be the generating factors for the occurrence of road
accidents. Similarly, in this study for the analyzed years (2020, 2021, and 2022), the curve
and the intersection represent the infrastructure elements with a high potential risk of acci-
dents (Table 1, number of accidents per year). Ref. [22] represents the source of statistical
data that are analyzed in the present section of the study.

Table 1. The situation of road accidents according to the characteristics of the road.

Road without Road Element

Year
Specific Elements Curve Intersection
2020 4092 1037 1061
2021 3332 744 790
2022 3138 739 795

The global analysis of the fatality index for the time period of 2020 to 2022 shows
comparable values for the accidents in the case of the curve as the main characteristic of
the road and for the case of the road without any specific characteristics (e.g., without
curve or/and intersection—Figure 2). Although serious road accidents occur more fre-
quently in intersections than in curves, the comparative statistical analysis indicates that the
number of fatalities is lower in the intersection events (Table 2). It can also be mentioned
 2020 304 975 1037 188 996 1061
2021 299 619 744 176 678 790
2022 293 601 739 177 686 795

Table 3. Fatality index.

Infrastructures 2024, 9, 154 8 of 22
Road Element
Year Road without Specific Elements
Curve Intersection
2020 27.3 29.3 17.7
that the
2021highest rate was recorded
38.2 for serious accidents
40.2 in the case of the two analyzed
22.3
characteristics,
2022 curve and intersection
39.6 (Figure 3, Table
36 3). 22.3

Road without specific elements Curve Intersection

45
40
Fatality index (%)
35
30
25
20
15
10
5
0
2020 2021 2022

Analyzed year

Figure 2. Comparative analysis of fatality index.

Figure 2. Comparative analysis of fatality index.

Table 2. Serious road accidents depending on road characteristics.

Curve Intersection
Year
Fatalities Serious Injuries Serious Accidents Fatalities Serious Injuries Serious Accidents
2020 304 975 1037 188 996 1061
2021 299 619 744 176 678 790
Infrastructures 2024, 9, x FOR PEER REVIEW 9 of 23
2022 293 601 739 177 686 795

2020 2021 2022

Serious accidents
Intersection

Serious injuries
Type of road accident

Fatalities

Serious accidents
Curve

Serious injuries

Fatalities

0 500 1000 1500 2000 2500 3000

Number of road accidents
Figure 3. Accident analyses for the period 2020–2022.
Figure 3. Accident analyses for the period 2020–2022.
4. Methodology
3. Fatality
TableThe literatureindex.
regarding the vehicle ditch accident type is relatively limited [17], an
experimental study being complex, expensive, and involving a considerable volume of
work. A viable alternative Roadconsid-
Element
Year Roadsolution
withoutisSpecific
the software simulation of such a situation,
Elements
Curve deformations,Intersection
ering as input data all the involved elements (e.g., vehicle rest position,
road sector
2020 geometrical parameters,27.3 ditch main dimensions, weather 29.3condition, etc.). 17.7
Through simulation,
2021 realistic results can
38.2 be obtained and valuable information
40.2 regarding 22.3
the dynamics
2022 of this impact type (vehicle39.6 and occupants). 36 22.3
In the case of vehicle overturning or rollover, the strength of the vehicle body is an
essential fact from the point of view of deformation amplitude, correspondence with oc-
cupant injury being a major factor regarding passive safety improvements.
Generally, overturning accidents have as the main cause cornering at high speeds,
when the centrifugal force of the vehicle’s mass is high enough to generate the overturning
moment. A particular situation is represented by the impact of the wheels from one side
of the vehicle with an obstacle on the roadside (ditch, curb), with overturning either or
Infrastructures 2024, 9, 154 9 of 22

4. Methodology
The literature regarding the vehicle ditch accident type is relatively limited [17], an ex-
perimental study being complex, expensive, and involving a considerable volume of work.
A viable alternative solution is the software simulation of such a situation, considering as
input data all the involved elements (e.g., vehicle rest position, deformations, road sector
geometrical parameters, ditch main dimensions, weather condition, etc.). Through simula-
tion, realistic results can be obtained and valuable information regarding the dynamics of
this impact type (vehicle and occupants).
In the case of vehicle overturning or rollover, the strength of the vehicle body is
an essential fact from the point of view of deformation amplitude, correspondence with
occupant injury being a major factor regarding passive safety improvements.
Generally, overturning accidents have as the main cause cornering at high speeds,
when the centrifugal force of the vehicle’s mass is high enough to generate the overturning
moment. A particular situation is represented by the impact of the wheels from one side of
the vehicle with an obstacle on the roadside (ditch, curb), with overturning either or not
preceded by skidding.
During the movement of the vehicle, sudden variations in the transversal inclination
of the vehicle body appear as a result of the vehicle wheels from one lateral side passing
over the ditch. The imbalances of the vertical reactions on the wheels generate a moment
that produces overturning and eventually subsequent rolling.

4.1. Preliminary Data

As mentioned and illustrated previously, the present paper was inspired by specific
traffic accidents (vehicles that run off into ditches) produced on the E68 (DN1) in Romania
on the Bras, ov–Făgăras, sector; one important aggravating factor is the unforgiving roadsides,
and bad weather conditions are also another element to be considered.
To carry out the study a relevant curved road sector with an unforgiving continuous
element was chosen (Figure 4), where the main geometrical parameters of the ditch were
Infrastructures 2024, 9, x FOR PEER measured.
REVIEW Other relevant geometrical elements (e.g., curve radius) of the considered road
10 of 23
sector were imported from Google Maps application in the simulation software, including
the map zone.

Figure4.4.E68
Figure E68(DN1)—curved
(DN1)—curved road sector used
road sector usedfor
forthe
thestudy.
study.

4.2. Accident Simulation Scenario

For the simulation of vehicle–ditch collision, the specialized software PC-Crash 13.0
was used, that enables the reconstruction and analysis of various traffic accidents. The
simulation goal was to investigate the cumulated effect of certain factors—curved road,
weather conditions, unforgiving roadsides—over vehicle dynamics and occupant injury
in the case of a vehicle that skids and runs off into the ditch, shown in Figure 4. The sim-
ulation scenario is a complex one and needs to consider and model a lot of parameters
Infrastructures 2024, 9, 154 10 of 22

The aspects from photos regarding the vehicle positions, materialized damages, road
conditions and roadsides represented the starting point in the development of the simula-
tion, which allows the analysis of the dynamics of the accident.

4.2. Accident Simulation Scenario

For the simulation of vehicle–ditch collision, the specialized software PC-Crash 13.0
was used, that enables the reconstruction and analysis of various traffic accidents. The
simulation goal was to investigate the cumulated effect of certain factors—curved road,
weather conditions, unforgiving roadsides—over vehicle dynamics and occupant injury in
the case of a vehicle that skids and runs off into the ditch, shown in Figure 4. The simulation
scenario is a complex one and needs to consider and model a lot of parameters regarding
road configuration, vehicle and occupant dynamics, including weather conditions that
favor the occurrence of the event.
In order to generate the accident scene, the specific zone from Google Maps was
Infrastructures 2024, 9, x FOR PEER REVIEW 11 of 23
imported in the PC-Crash 13.0 software, then a 3D road object tool was used to generate the
specific road configuration, including the main ditch geometrical parameters (Figure 5).

Figure 5. Simulation scene, ditch profile—E68 (DN1).

Figure 5. Simulation scene, ditch profile—E68 (DN1).

The simulation was conducted for rainy weather conditions, a preponderant scenario
for such accident occurrence, and the coefficient of friction between wheels and carriageway
was adopted accordingly (wet conditions).
As the vehicle for the simulation, an SUV type was used as this kind of vehicle is
very popular in EU (in Romania, too). The vehicle dynamic parameter setup (e.g., speed,
acceleration, braking, etc.) was made according to the geometrical road configuration and in
such a manner as to accurately simulate a real-life vehicle skidding in the initial phase of the
vehicle’s movement into the curve, and after that the vehicle runoff into the ditch. In order
to obtain a realistic accident mechanism and dynamics, the simulation parameters were
continuously modified and optimized through iterations (e.g., speed, acceleration, braking,
reaction time, etc.), until boundary conditions—vehicle rest position—were obtained.
For the calculation of movements and loads for vehicle occupants with PC-Crash
software, the multibody model was used (Figure 6). Interaction of the occupants with the
vehicle interior was also considered. Two restrained occupants were placed in the vehicle,
on front seats in order to examine the motion during the impact. The individual bodies
of the multibody system are interconnected by joints and for restrained occupants, seat
belts are modeled using spring damper elements. In the multibody model, for each body

Figure 6. Multibody model used in simulation.

Infrastructures 2024, 9, 154 11 of 22

different
Figure properties
5. Simulation can be
scene, specified,
ditch like: geometry
profile—E68 (DN1). (a body being defined as an ellipsoid),
mass, moments of inertia, contact stiffness, and coefficients of friction [23].

Figure 6. Multibody
Figure model
6. Multibody modelused
usedin
in simulation.
simulation.

In Romaniathe
In Romania thespeed
speed limit
limitononEuropean
Europeannational roadsroads
national is 100 is
km/h. On the On
100 km/h. considered
the consid-
road sector, the input data for the simulation are detailed in Table 4.
ered road sector, the input data for the simulation are detailed in Table 4.
Table 4. Simulation input data.

Vehicle Type SUV, 4WD

Vehicle speed before entering the curve 90 km/h, case (a) and (b)
Friction coefficient, wet conditions 0.5
Maximum deceleration, wet conditions 4.91 m/s2
Multibody model 2 front belted occupants: 80 kg, 1.8 m height each

4.3. Simulation Results

The performed simulation considered two possible scenarios inspired by accidents
presented in Figure 1 and are presented as follows:
(a) The vehicle entering into the curve is skidding, leaves the road, and enters into the
ditch alongside with its direction of movement.
(b) On entering the curve, the vehicle skids, enters on the opposite direction, and falls into
the ditch on the left side of its travel direction. This scenario excluded the possibility
of an impact with a vehicle coming from the opposite direction as this aspect is not
the object of the present study.
For the proposed scenarios, the performed simulation revealed that the accident
occurrence mechanism consists of two different phases: initially, the vehicle skidding
appears to be due to the centrifugal force, and then the vehicle overturning and/or rollover
is generated by the vehicle–ditch impact. In this case the vehicle overturning occurs
independently of the road adhesion, being caused by the moment of the impact force.
These two phases are illustrated in Figures 7 and 8, that consist of successive frames of
the accident dynamics at time intervals of 0.4 s for both analyzed cases. In Figures 9 and 10
 currence mechanism consists of two different phases: initially, the vehicle skidding ap-
pears to be due to the centrifugal force, and then the vehicle overturning and/or rollover
is generated by the vehicle–ditch impact. In this case the vehicle overturning occurs inde-
pendently of the road adhesion, being caused by the moment of the impact force.
Infrastructures 2024, 9, 154
These two phases are illustrated in Figures 7 and 8, that consist of successive frames 12 of 22
of the accident dynamics at time intervals of 0.4 s for both analyzed cases. In Figures 9 and
10 the vehicle overturning and rollover for the same time intervals are detailed and for
the vehicle overturning and rollover for the same time intervals are detailed and for
both cases.
both cases.

Infrastructures 2024, 9, x FOR PEER REVIEW 13 of 23

Figure 7. Consecutive simulation sequences at time intervals of 0.4 s—case (a).

Figure 7. Consecutive simulation sequences at time intervals of 0.4 s—case (a).

Figure 8. Consecutive
Figure 8. Consecutive simulation
simulation sequences
sequences at
at time
time intervals
intervals of
of 0.4
0.4 s—case
s—case(b).
(b).
Infrastructures 2024, 9, 154 13 of 22

Figure 8. Consecutive simulation sequences at time intervals of 0.4 s—case (b).

Infrastructures 2024, 9, x FOR PEER REVIEW 14 of

Figure 9. Vehicle overturning phase—case (a).
Figure 9. Vehicle overturning phase—case (a).

In both cases, the skidding phase begins with an instability of the movement, due to
the inappropriate behavior of the driver, who did not adapt the speed properly to the road
conditions (one of the significant factors that generates accidents in Romania).
The skidding phase that appears is characterized by additional energy consumption
due to vehicle lateral deviation and rotation tendency, the friction with the road surface
being more intense. The energy consumption is equivalent to the increase in rolling re-
sistance. This phase is considered to be ended when the vehicle leaves the carriageway
and starts to fall into the ditch.

Figure 10. VehicleFigure 10. Vehicle

overturning overturning
phase—case (b).phase—case (b).

In both cases, theFigures 11 and

skidding 12 show
phase beginsthewith
vehicle speed variation
an instability of theinmovement,
time. In casedue(b)tocompared
the inappropriate(a),behavior
the vehicle speed
of the at the
driver, time
who didwhen it starts
not adapt thetospeed
enter properly
into the ditch
to theisroad
lower, 65 km
conditions (one versus 79 km/h, thefactors
of the significant initial that
speed being theaccidents
generates same in both cases. In case (b) the higher init
in Romania).
The skiddingspeed decrease
phase is determined
that appears by cumulated
is characterized factors, such
by additional as: driver
energy reaction and braki
consumption
attempt, the vehicle that is skidding and enters in the opposite
due to vehicle lateral deviation and rotation tendency, the friction with the road surface direction (the space tra
being more intense. The energy consumption is equivalent to the increase in rolling time th
eled on the carriageway is superior). Those elements generated a supplementary
resistance. This allowed,
phase is through
consideredcontrolled and uncontrolled
to be ended actions,leaves
when the vehicle a lower impact
the speed of the vehi
carriageway
with the ditch,
and starts to fall into the ditch.theoretically with a direct effect on the occupant level of injury (but this
relative, depending also on the impact incidence angle of the vehicle).
Figures 11 and 12 show the vehicle speed variation in time. In case (b) compared to (a),
the vehicle speed at the time when it starts to enter into the ditch is lower, 65 km/h versus
79 km/h, the initial speed being the same in both cases. In case (b) the higher initial speed
decrease is determined by cumulated factors, such as: driver reaction and braking attempt,
the vehicle that is skidding and enters in the opposite direction (the space traveled on the
 Figures 11 and 12 show the vehicle speed variation in time. In case (b) compared to
(a), the vehicle speed at the time when it starts to enter into the ditch is lower, 65 km/h
versus 79 km/h, the initial speed being the same in both cases. In case (b) the higher initial
Infrastructures 2024, 9, 154 speed decrease is determined by cumulated factors, such as: driver reaction and 14 ofbraking
22
attempt, the vehicle that is skidding and enters in the opposite direction (the space trav-
eled on the carriageway is superior). Those elements generated a supplementary time that
carriageway
allowed, is superior).
through controlledThose
and elements generated
uncontrolled a supplementary
actions, a lower impact time that of
speed allowed,
the vehicle
through controlled and uncontrolled actions, a lower impact speed of the vehicle with the
with the ditch, theoretically with a direct effect on the occupant level of injury (but this is
ditch, theoretically with a direct effect on the occupant level of injury (but this is relative,
relative, depending also on the impact incidence angle of the vehicle).
depending also on the impact incidence angle of the vehicle).

Infrastructures 2024, 9, x FOR PEER REVIEW 15 of 23

Figure
Figure 11.11. Vehiclespeed—case
Vehicle speed—case (a).
(a).

Figure
Figure12.
12.Vehicle
Vehicle speed—case (b).
speed—case (b).

The danger of injury to the occupants occurs mainly during the overturning phase,
any intervention of the driver being excluded. The occupant level of injury depends in
this phase on the vehicle kinetic energy and the obstacle (ditch) profile.
Practically, the overturning phase into the ditch is the one that generates vehicle dam-
age and the injury level of the occupants, depending on the vehicle speed at the beginning
 Infrastructures 2024, 9, 154 15 of 22

The danger of injury to the occupants occurs mainly during the overturning phase,
any intervention of the driver being excluded. The occupant level of injury depends in this
phase on the vehicle kinetic energy and the obstacle (ditch) profile.
Practically, the overturning phase into the ditch is the one that generates vehicle
damage and the injury level of the occupants, depending on the vehicle speed at the
beginning of overturning or rollover and speed and acceleration variation during this
phase (the initial impact incidence angle has to be taken into account too).
From Figures 11 and 12, it can be seen that the speed drop (kinetic energy, too) during
the vehicle–ditch impact is determined by the following mechanism: vehicle body friction
with the ditch surface and vehicle body deformation.
The impact between vehicle body parts and the ditch surface is highlighted by the
acceleration graphs (longitudinal—long, lateral—lat, and vertical—vert), Figures 13 and 14.
A Channel Frequency Classes (CFC) 60 filter was used for processing the impact signals,
to eliminate the high-frequency noise and reduce the signal peaks. By comparing the
graphs for (a) and (b) cases, it can be seen that the vehicle acceleration dispersion, as impact
effect, is higher in case (a), but amplitudes are comparable. Thus, in case (a) predominant
are the longitudinal accelerations with a maximal magnitude about 50 m/s2 and lateral
accelerations are about 30 m/s2 , as a result of the vehicle sliding into the ditch. In (b) case a
high amplitude of accelerations is obtained during the rollover of the car, but compared
Infrastructures 2024, 9, x FOR PEER REVIEW to
16 of 23
(a), the time intervals where these peaks are obtained are narrow, about 0.5 s (interval 1,
value 40 m/s2 ) and 0.4 s (interval 2, value 85 m/s2 ).

Figure
Figure13.
13.Vehicle
Vehicleacceleration—case
acceleration—case(a).
(a).

The simulation frames and acceleration magnitude indicate an increased level of

vehicle body damages induced exclusively by contact with the ditch surface. In case (a) the
front and right side of the car are damaged. In (b) case, due to the vehicle overturn/partial
rollover the entire vehicle body is affected (after a specialized damage evaluation it could
be considered total damage).
As mentioned before, for the occupants’ kinematics the multibody module was used.
For them, important speed differences occur in the case of collisions with other vehicles
or obstacles. High accelerations appear when the vehicle, for example rotates around its
longitudinal axis (overturning or rollover).
After the multibody system simulation is performed, the most important data are
those related to accelerations, because the severity of the occupants’ injuries depends on
Infrastructures 2024, 9, 154 16 of 22

them. In the case of the current research, the most susceptible human body parts that can
be seriously injured are head and neck. This is because of the possibility of the head hitting
the car roof or practically with any hard parts inside the passenger compartment. In this
type of accident other elements that can influence the injury severity are: the vehicle size,
vehicle body deformation level, rollover number, obstacle size, obstacle that penetrates
Figure passenger
13. Vehicle acceleration—case
compartment, etc.(a).

Figure Figure
14. Vehicle acceleration—case
14. Vehicle (b).
acceleration—case (b).

After the multibody

In order system
to avoid simulation
head injury, is performed,
in theory the most
the acceleration important
magnitude datanot
should areexceed
those related to accelerations, because the severity of the occupants’ injuries
a certain level, as studied through the head injury criterion (HIC) that considers depends on the
them. In the case
duration andof severity
the current research,
of the impact.the most susceptible
According to [24] HIC human
is the body parts that parameter
most important can
be seriously injured
regarding are head
human and neck.
survival. This is because
It characterizes of the
the brain possibility
injuries of the impact
due to head hitting
of the head
the carinroof or practically
vehicle accidents. with any hard parts
An alternative insidemethod
evaluation the passenger
refers tocompartment. In this that is
average acceleration
type ofgreater
accidentthan 80 gelements
other for no longer than
that can 3 milliseconds
influence (ms).
the injury severity are: the vehicle size,
vehicle body In deformation
[25], it is mentioned that thenumber,
level, rollover human body supportability
obstacle limit
size, obstacle about 10–35 g, at
is penetrates
that
gradients
passenger etc. g/s with a maximum duration of 0.15–0.4 s. According to [26] the
of 500–1000
compartment,
Inhuman
order tobody
avoidexposure to acceleration
head injury, higher
in theory the than 30 gmagnitude
acceleration lasting longer thannot
should 0.2exceed
s may cause
fluidlevel,
a certain displacement
as studiedor through
tissue deformation. The symptoms
the head injury criterion appear as a blood
(HIC) that pressure
considers the drop,
pulse rate rise, weakness, and skin pallor. These aspects refer to a forward seated position.
In the backward-seated position, acceleration up to 35 g can be tolerated without significant
difficulties [26].
In the current study, in case (a) (Figures 15 and 16) the maximum obtained value
of head acceleration (right-side occupant) was about 240 m/s2 , 24 g, that correspond to
HIC15 < 130 (equivalent acceleration < 55, for 3 ms) inducing no concussion to the occupant,
possibly headache or dizziness, with effects for less than an hour according to [27].
In case (a) the vehicle entered tangentially into the ditch and an important amount of
the kinetic energy of the vehicle was dissipated through the friction between the lateral
side and the ditch wall, an effect that contributes to non-injury of the occupants (but this
is a particular aspect induced by particular dynamics) and only some temporary, minor
effects. For the right-side occupant, the acceleration is higher due the fact that the vehicle
hits the ditch first with its right lateral side.
 with effects for less than an hour according to [27]. The maximum value for acceleration
for the right-side occupant was about 412 m/s2, 41 g, a value that corresponds to HIC15
180, the occupant suffering mild concussion according to [27].
In the analyzed (b) scenario, the vehicle overturn (partial rollover) induced higher
Infrastructures 2024, 9, 154 17 of 22
accelerations for both occupants, which indicates a different mechanism of kinetic energy
dissipation for that impact type.

Infrastructures 2024, 9, x FOR PEER REVIEW 18 of 23

Figure 15.
Figure 15. Driver
Driver acceleration—case
acceleration—case (a).
(a).

Figure 16.16.
Figure Front right-side
Front right-sideoccupant
occupant acceleration—case (a).
acceleration—case (a).

In case (b) (Figures 17 and 18) the maximum value obtained for the acceleration
for the driver’s head was about 210 m/s2 , that correspond to HIC15 < 130 (equivalent
acceleration < 55, for 3 ms) inducing no concussion to the driver, possibly headache or
dizziness, with effects for less than an hour according to [27]. The maximum value for
acceleration for the right-side occupant was about 412 m/s2 , 41 g, a value that corresponds
to HIC15 180, the occupant suffering mild concussion according to [27].
In the analyzed (b) scenario, the vehicle overturn (partial rollover) induced higher
accelerations for both occupants, which indicates a different mechanism of kinetic energy
dissipation for that impact type.
Infrastructures 2024, 9, 154 18 of 22
Figure 16. Front right-side occupant acceleration—case (a).
Figure 16. Front right-side occupant acceleration—case (a).

Figure 17.
Figure 17. Driver
Driver acceleration—case
acceleration—case (b).
(b).
Figure 17. Driver acceleration—case (b).

Figure 18. Front right-side occupant acceleration—case (b).

Figure
Figure 18.
18. Front
Front right-side
right-side occupant
occupant acceleration—case
acceleration—case (b).
(b).

5. Discussions and Recommendations

The majority of the accidents involving vehicle overturning or rollover occur outside
the carriageway (the vehicle leaves the road and enters the roadside), this type of accident
being considered as a run-off-road accident [14]. Every such accident is unique due to
its particularities: vehicle type and load, terrain characteristics, obstacles, road design,
driver experience and perception, the incidence angle of the impact, obstacle dimensions,
etc. If the vehicle during the rollover does not hit any obstacles this kind of accident is
less dangerous due the fact that vehicle kinetic energy is dissipated over a longer time
compared to a crash between two vehicles.
The objective of the present study was to particularize and analyze the situation when
the vehicle’s overturn or rollover was induced by an unforgiving roadside, as the effect of
a run-off-road phenomenon. Simulation results show major damage of the vehicle body
induced exclusively by the impact with the ditch and obviously a considerable repair cost.
In the situation of vehicle rollover, the necessity to replace the car with a new one may have
to be considered.
Infrastructures 2024, 9, 154 19 of 22

From the performed analysis results that the ditch represents an unforgiving roadside,
because due to human error, it caused the actual accident, as it was in contradiction with the
concept of a forgiving roadside [1,14]. Through this idea, in the case of a run-off vehicle, the
roadside through its design, must either avoid the accident or minimize its consequences.
In this context the most important factor is the health and safety of the occupants
and as could be observed this type of accident can affect this in a certain manner. A more
dangerous scenario, compared to the analyzed one, could appear anytime in the case of
some other types of vehicles, if the driver/occupants are not seat-belted, with different
vehicle dynamic parameters, especially including a different vehicle incidence angle with
the obstacle (ditch). Different dynamic conditions than those analyzed in the present paper
could generate serious injury and vehicle damage.
For both studied cases, the vehicle damages took precedence compared to the level of
occupant injury, this being a positive aspect of the research. The injury level was a little
bit more serious in case (b). Both scenarios had as starting point the inappropriate road
configuration estimation by the driver, materialized by over speeding in wet conditions
(a frequent real scenario). Even if the injury level obtained through PC-Crash software
simulation was not a significant one for the front occupants, the potential psychological
trauma cannot be ignored.
From the presented aspects, the study highlights the influence of an improper roadside
design over traffic safety in the case of human error occurrence. Another relevant element
that results from the research is the importance of auditing problematic road sectors in
order to implement on existing roads the forgiving roadside systems.
Following the elements detailed before in the paper, for the analyzed problem (ditch–
vehicle impact) as recommendation, the next solutions can be implemented in order to
transform an unforgiving roadside into a forgiving one:
• Cover the ditch and create a safety zone in the proximity of the carriageway, combined
with the measure of eliminating extra potential obstacles in problematic areas with a
high rate of roadsides accidents. In this manner the vehicle that is out of control will
pass over the covered ditch and there will exist the possibility to regain its control or
to stop on the field without major or zero damages. It is necessary that the adherence
of the covering material be close to that of the asphalt one. This fact is illustrated in
Figure 19, where by such a measure, the covered ditch with an appropriate carriageway
shoulder represents a recovery area, which will allow the driver in limit situations to
perform recovery maneuvers. The effect will be injury free occupants and a vehicle
free of damages.
• Modify ditch slope ratio; the slopes should be kept as shallow as possible. A shallow
slope will allow the driver to regain control over the vehicle (Figure 20) [14].
• Isolate the ditch by mounting appropriate roadside barriers (e.g., rolling barrier), that
will minimize the effects of a vehicle out of control. This is recommended where a
previous solution is not possible through environmental limitations (Figure 21).
• Enlarge and pave the road side shoulder (Figure 22), and by that measure, in reasonable
limits, a recovery zone is created for the drivers (where it is possible on existing roads),
in a similar way to the ditch covering solution presented previously. This is known as
a safety zone, where a driver can regain the control over the vehicle.
In this study, a few possible solutions were indicated, through which implementation
of real conditions a reduction in frequent roadsides accidents was created and an increase
of traffic safety in any conditions obtained, both on the studied road sector and in general
on Romanian national roads. The paper had in mind the evaluation of vehicle damage level
and occupant injury severity for a simulated situation, inspired by real traffic accidents on
the same European road sector. On the other hand, the paper can be seen as an input study
for also implementing the concept of forgiving roads in Romania, with real life benefits in
reduction of traffic accident and their injury severity.
 • willEnlarge
minimize andthepave theofroad
effects side shoulder
a vehicle (FigureThis
out of control. 22),isand by that measure,
recommended whereina reason-
able limits,
previous solution a recovery zone through
is not possible is created for the drivers
environmental (where it(Figure
limitations is possible
21). on existing
• roads),
Enlarge andin a similar
pave way
the road toshoulder
side the ditch(Figure
covering
22),solution
and by thatpresented
measure,previously.
in reason- This is
ableknown
limits, aasrecovery
a safetyzone
zone,iswhere
createda for the drivers
driver (where
can regain the itcontrol
is possible
overon
theexisting
vehicle.
Infrastructures 2024, 9, 154 roads), in a similar way to the ditch covering solution presented previously. This is 20 of 22
known as a safety zone, where a driver can regain the control over the vehicle.

Figure
Figure 19. The effect 19. The
of covered effect
ditch of covered ditch solution.
solution.
Figure 19. The effect of covered ditch solution.

Figure
Figure 20.Figure
Examples
20. Examples ofditch
of safe
20. safe ditch
Examples safe[14].
[14].
of ditch [14].

The forgiving road concept, through its multiple possible technical solutions, will
increase road safety and through it, the confidence of all traffic participants during usage
of the Romanian national road network.
The study also reveals the practical utility of developing a road safety system, includ-
ing adequate technical solutions to transform a road into a forgiving one with direct effect
on traffic safety. From this point of view the relevant technical solutions and good practices
experience can be the starting point for a standardization in the field of road safety.
Infrastructures 2024,
Infrastructures 9, x9,FOR
2024, 154 PEER REVIEW 2121 of 23
of 22
Infrastructures 2024, 9, x FOR PEER REVIEW 21 of 23

Figure
Figure21.
Figure 21.Rolling
21. Rollingbarrier
Rolling barrier[28].
barrier [28].
[28].

Figure 22.
22. Enlarge
Enlarge and
and pave
pave the
the road
road side
side shoulder—safety zone.
zone.
Figure
Figure 22. Enlarge and pave the road side shoulder—safety
shoulder—safety zone.

In this study, a few possible solutions were indicated, through which implementation
In this study, a few possible solutions were indicated, through which implementation
of real conditions
Funding: a reduction
This research in external
received no frequentfunding.
roadsides accidents was created and an increase
of real conditions a reduction in frequent roadsides accidents was created and an increase
of traffic safety in any conditionsThe data obtained, both within
are contained on the studied
article.road sector and in general
ofData Availability
traffic safety inStatement:
any conditions obtained, both on thethestudied
on Romanian national roads. The paper had in mind the evaluation of vehicle damage
road sector and in general
onAcknowledgments:
Romanian
level national
and occupant The roads.
author
injury is The
severity paper
grateful
fortoa thehad in mind
Transylvania
simulated the evaluation
University
situation, byofreal
of Brasov
inspired vehicle
for trafficdamage
technical and
acci-
level and
financial occupant
support. injury severity for a simulated situation,
dents on the same European road sector. On the other hand, the paper can be seen as an inspired by real traffic acci-
dents
inputon
Conflicts the
study same European
for also
of Interest: implementing
The authors road sector.
declarethe On the
noconcept
conflicts ofother
of hand,
forgiving
interest. the paper
roads can bewith
in Romania, seenreal
as an
input study for also implementing the concept of forgiving
life benefits in reduction of traffic accident and their injury severity. roads in Romania, with real
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