comparative evaluation for pedestrian safety systems · comparative evaluation for pedestrian...

ISSN : 2319 – 3182, Volume-2, Issue-4, 2013

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Comparative Evaluation for Pedestrian Safety Systems

Mukesh Chaudhari

E-mail : [email protected]

Abstract – Pedestrian injuries, fatalities, and accessibility

continue to be a serious concern in India and also across

the world. There are major two systems used to protect the

pedestrian from injury or death. Collisions between

pedestrians and road vehicles present a major challenge

for public health and traffic safety professionals.

Pedestrian safety is a complicated problem due to the

many variables that comprise the built environment and

the complexity of understanding behavioral decision-

making and outcomes. This literature review explores

recent research on the roles of human factors and

environmental factors in vehicle-pedestrian crashes,

including a brief summary of recent sources that address

countermeasures to improve the safety of the physical

environment for pedestrians. Adult skull and face injuries

in car pedestrian accidents is account for 60 percent of all

pedestrian serious injuries, whereas 18 percent of skull

injuries were due to the structure of bonnet. The above

values show the essential to think more carefully the role of

the bonnet in pedestrian skull safety. In 2010, 4,280

pedestrians were killed and an estimated 70,000 were

injured in traffic crashes in the United States. On average,

a pedestrian was killed every two hours and injured every

eight minutes in traffic crashes. Pedestrians are the main

fatality of fatal accidents. Nearly 90 percent of the total

fatalities in our country occur on rural roads while only 10

percent occur on urban roads. Conventional planning is

greatly biased to the motorized modes of transport, even

though every road users is a pedestrian at some stage of

journey. The problem is realized but efforts are negligent;

therefore, authors suggest the need to address it within an

integrated system of roads, road users and vehicles. As

automobile transportation continues to increase around

the world, bicyclists, pedestrians, and motorcyclists, also

known as Vulnerable Road Users (VRU), will become

more susceptible to traffic crashes, especially in countries

where traffic laws are poorly enforced.

Keywords – bonnet, head injury, optimal design, Pedestrian

safety

I. INTRODUCTION

A large proportion of the vehicular population

enlargement in the country has taken place in the towns

and cities. As towns and cities expand the outing lengths

increase. Provision of public transport services has not

matched the demand, culminating in large number of

personalized modes on road. The supply of road

infrastructure has also fallen short of the requirements.

As a result, the congestion on roads has increased

beyond capacity leading to delay, fuel loss, accidents

and environmental pollution. Safety of operation is an

area of concern in all modes of transport including walk

mode. Though the accident rate is coming down, the

number of fatalities is still high.

As automobile transportation continues to boost

around the world, bicyclists, pedestrians, and

motorcyclists, also known as Vulnerable Road Users

(VRUs), will become more at risk to traffic crashes,

especially in countries where traffic laws are poorly

enforced. In particular, nations such as India and China,

which have growing populations as well as a growing

middle class, will see a substantial increase in traffic

injuries and fatalities if strategies are not found to ensure

the safety of Vulnerable Road Users. Many countries,

however, are employing innovative strategies to ensure

that road users can more safely navigate the urban

landscape. While bicyclists and motorcyclists are

important road users, this paper will focus on pedestrian

crash problems and solutions. Pedestrians are most at

risk in urban areas due in part to the large amount of

pedestrian and vehicle activity in urban areas. No matter

if the primary mode of transportation is the automobile,

bicycle, or public transportation; people must walk as a

part of the trip, such as from their home to the store or

place of employment, and/or to the transportation stop.

Fig.1: Distribution of Road Traffic Fatalities by Road

User Group [2]

International Journal on Theoretical and Applied Research in Mechanical Engineering (IJTARME)


32

With this in mind, designing safe, accessible, and

comprehensive facilities for pedestrians is vital to

reducing pedestrian crashes. Beginning with pedestrian

safety statistics at the global, regional, and national

levels, this paper will address potential countermeasures

and strategies for improving pedestrian safety from an

international perspective.

As expected, more crowded countries will have

higher total numbers of pedestrian deaths with China,

India, and the Russian Federation in first, second, and

third in that category, respectively.

Fig. 2: Number of Pedestrian Deaths by Country [3.0]

A Research on adult pedestrian protection currently

is focusing mainly on passenger cars and commercial

vehicles. However, impacts with heavy goods vehicles

and buses are also important, especially in urban areas

and in developing countries. Pedestrian safety is the

important issues across the world. Transportation

network is a heart of a nation and transport services are

considered as growth engine of economy. Thousands of

pedestrians are killed or badly injured in automotive

accidents annually. According to the National Highway

Traffic Safety Administration (NHTSA), In 2010,

32,885 people died in motor vehicle traffic crashes in

the United States—the lowest number of fatalities since

1949 (30,246 fatalities in 1949) This was a 2.9-percent

decline in the number of people killed, from 33,883 in

2009, according to NHTSA‘s 2010 Fatality Analysis

Reporting System (FARS). In 2010, an estimated 2.24

million people were injured in motor vehicle traffic

crashes, compared to 2.22 million in 2009 according to

NHTSA‘s National Automotive Sampling System

(NASS) General Estimates System (GES). This slight

increase (1.0% increase) in the estimated number of

people injured is not statistically significant from the

number of people injured in crashes in 2009 [1].

The above values show the need to consider

carefully the bonnet of the passenger car to ensure

pedestrian safety. As traffic safety emphasizes

pedestrian protection, ‗pedestrian safety systems‘ were

designed to protect pedestrians. Two main approaches

have been developed to protect pedestrians against the

effects of automotive accidents. The first approach is

active protection, which involves sensors placed in

automobiles to detect oncoming pedestrians and

potential accidents, and it subsequently offers solutions

to avoid accidents [4]. Although this approach can be

solved efficiently and offers an efficient means of

responding to safety problems, the sensor system which

must be installed in the car is more expensive and

required more care. Also the sensor system is activated

when the vehicles crashes to any other objects, beams,

dividers, etc The second approach is passive protection,

in which design measures are implemented either to

protect pedestrians from injury or to minimize the

severity of potential injury [4]. For instance, passenger

cars can be equipped with advanced devices such as

external air bags and lifting-bonnet systems [10–12],

which reduce pedestrian injuries in the event of

accidents. All solutions are continuously developing

because each solution highlights the role of automobile

owners for protecting pedestrians. There are mainly two

systems to protect the pedestrian from collision with

vehicle, one is pop-up hood system and second is to

optimize the bonnet thickness for pedestrian safety.

II. POP-UP ENGINE HOOD SYSTEM

This section describes the basic structure and

mechanisms of the pop-up engine hood system. As

illustrated in Fig. 2, the system consists of the following

three basic components.

Fig.3 : Pop-up hood system. [5]

(1) Sensors: Detect a collision between the vehicle and

a pedestrian.

Fig. 4 : Sensing system. [6]



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(2) Control unit: Judge the necessity of raising the

hood.

(3) Actuators: Raise the rear of the hood.

The function of each component is explained in

detail below.

Sensors - Three sensors for detecting a collision with a

pedestrian are installed behind the front bumper fascia

as shown in Fig. 3. This structure was adopted because

the front bumper is usually the first part to come in

contact with a pedestrian's body in a collision with a

vehicle. The sensors are positioned on the right and left

sides and in the center. The sensors function to detect a

change in acceleration and have experience of use as the

airbag sensors. These devices detect the movement of

the bumper fascia caused by contact with a pedestrian's

legs.

Fig. 5. Sensor for pedestrian detection. [5]

Actuators - The actuators that provide the driving force

for raising the rear of the hood are constructed with an

extendable cylinder operated by pyrotechnics. As shown

in Fig. 5, the length of the three-stage cylinder before

operation is less than one-half of its extended size.

Fig. 6. Actuator. [5]

Figure 6 shows the relationship between the

operation of the actuators and the hood hinges for

opening/closing the hood. Normally, the hood opens or

closes by rotating upward or downward centered on the

hood hinges (Fig. 6 (a) and (b)). In contrast, when the

pop-up system is deployed, the rear of the hood is raised

centered on the hood lock at the front of the vehicle

(Fig. 6 (c)).

The hood hinge adopted is a link type hinge, as

shown in Figure 5. The link hinge is composed of an

upper bracket, lower bracket, arm A, arm B, three

pivots, and a pin. According to an ignition signal from

the ECU, gas from the micro gas generator raises the

shaft. The shaft shears the hood hinge pin, lifting the

rear portion of the hood approximately 100mm, thereby

providing a space between the hood and the hard

components under the hood, such as the engine.

Before operation after operation

Fig. 7. Hood hinge of link type. [7]

Fig. 8. Operation of hinge and actuator.[8]

A detailed diagram of the hood hinge mechanism is

shown in Fig. 7. During normal opening or closing of

the hood, the lock lever fixes link (a) and link (b),

allowing only link (a) to rotate. When the pop-up hood

system is deployed, the actuator head presses on the

lock lever, allowing link (b) to rotate. The actuator

cylinder extends to raise the rear of the hood, with the

hood lock serving as the fulcrum of the hood's upward

rotation. As a result of these operations, the rear of the

hood is raised by approximately 100 mm to secure

buffer space between the hood and the high-stiffness

parts beneath it.



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Fig. 9. Pop-up mechanism of hood hinge. [9]

Collapsible Mechanism of Actuators:-

This section presents an example of numerical

simulations [5], [6] that were conducted to validate the

effectiveness of the collapsible mechanism of the

actuators. These simulations were performed with the

PAM-CRASH.

Software using a headform impactor. Figure 8

shows acceleration histories of the headform impactor

when it struck the hood surface near one of the

actuators. The impactor acceleration is indicated along

the vertical axis in relation to its displacement along the

horizontal axis. The solid line is for a pop-up hood

system with collapsible actuators and the dashed line is

for a system with rigid actuators. The waveform for the

system without the collapsible mechanism indicates that,

following the initial peak for the primary impact with

the hood surface, the secondary impact with the actuator

produced a relatively large acceleration peak. In

contrast, the waveform for the system with the

collapsible mechanism indicates that the actuators

initially supported the rear of the hood until the preset

load was reached, after which the collapsible

mechanism worked to avoid another increase in

impactor acceleration. As a result, the system with the

collapsible mechanism kept the subsequent impactor

acceleration below that of the level of the primary

impact with the hood, thereby verifying the

effectiveness of this mechanism.

Validation of System Deployment Completion Time –

In order to validate that the pop-up engine hood

system could be deployed before the targeted system

deployment completion time explained in the preceding

section, tests were conducted with impactors that

simulated the mass of pedestrians. Figure 10 shows an

example of the displacement history of the pop-up hood,

where the amount of hood displacement near the

actuators is shown along the vertical axis in relation to

elapsed time along the horizontal axis. The results

indicate that the hood was raised the specified amount

with sufficient time to spare in relation to the targeted

deployment time from the moment of the impactor

contact with the front bumper.

Fig. 10. Example of displacement history of pop-up. [8]

Method of Evaluating Head Protection Performance

The headform impactor was projected against the

hood and other areas of the vehicle front-end to

investigate head protection performance, which was

evaluated using the head injury criterion (HIC) as

defined in Eq. (1) below.

With the condition

Where A is the acceleration of the headform impactor

and t1 and t2 are the initial and final times. In order to

reduce the HIC, the mean acceleration should be low

and there should not be any pronounced acceleration

peak.

III REDESIGNING THE BONNET FOR

PEDESTRIAN SAFETY

Redesigning the structure of the bonnet to improve

pedestrian protection has recently received considerable

attention by automobile manufacturers and industry,

institutes. Figure 11 illustrates a method of protecting

pedestrians by creating more holes in the ribs of

reinforcement to reduce the bonnet stiffness [11].

Previous research on improving pedestrian safety also

increased the number of ribs to create a bonnet surface

with more uniform stiffness [13]. Figure 12 shows the

reinforcement structure developed to protect pedestrians

in accidents. Currently, some automobiles use a multi-

cone structure (Fig. 12) instead of a rib structure for

bonnet reinforcement.



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It is very important to select the most helpful

thicknesses of the bonnet skin and bonnet reinforcement

for each bonnet structure. Kalliske and Friesen [14]

reduced the bonnet stiffness and mass by reducing the

bonnet skin thickness to protect the pedestrian head.

However, this research did not expose the basis for

selecting the bonnet skin thickness. This research has

simply reduced the bonnet skin thickness rather than

seeking a basis for optimizing the values. Moreover, the

bonnet stiffness must be systematically optimized

because some components within the engine

compartment can often be very close to the bonnet

surface and these components can damage the skull of

human head when collision occurs.

Fig. 11 Pedestrian protection by the modified original

reinforcement structure [11]

If the bonnet has poor stiffness, there is a risk that

components within the engine compartment may strike

the bonnet during collision, increasing the danger to the

pedestrian and negating the benefits of the reduced

stiffness. Therefore, bonnet redesign not only must

simply reduce the bonnet stiffness and mass but also

should consider the bonnet deflection during collision.

Presently there are two methods for evaluating

pedestrian injury. The first method uses pedestrian

impactors to evaluate corresponding areas on the

vehicle. The second method uses a complete dummy to

evaluate the vehicle‘s frontal structure. Both the

complete dummy and the pedestrian impactor methods

require complicated physical testing systems.

Furthermore, the pedestrian impactors must pass a series

of tests to obtain certification. Testing the material

properties of pedestrian impactors is time consuming.

Numerical simulation offers another reliable method of

solving the above problems. One advantage of this

method is its ability to solve optimization problems.

While mathematical analysis is not an easy method of

solving optimization problems, analysis of simulation

results is relatively simple and effective. Because of the

above advantages, all pedestrian-head-to-bonnet-top

tests in this study will be performed using numerical

simulation.

Fig. 12 The solution of an alternative design for

protection of the pedestrian head [13]: (a) traditional

design; (b) increased number of ribs; (c) multi-cone

design

This study analyses the effects of the bonnet skin

and bonnet reinforcement thickness on pedestrian head

injury by performing number of simulation of head form

impactor to bonnet top test as per European Enhanced

Vehicle-safety Committee (EEVC) Working Group 17

(WG17) regulations using different thicknesses. Many

points on the bonnet surface will be considered to

enhance pedestrian friendliness by using this method. A

bonnet with the optimal thicknesses not only is

pedestrian friendly but also is as stiff as possible. Based

on the proposed method, this study presents steps for

optimizing the bonnet skin and bonnet reinforcement

thicknesses for a particular automobile model.

1 SIMULATION OF PEDESTRIAN-HEAD-TO

BONNET TESTS

1.1 Pedestrian-head-to-bonnet tests

The European Commission also published a directive

to assess the level of pedestrian protection for vehicle

fronts in 2003. The European Parliament supported the

commitment on pedestrian safety proposed by the

European Automobile Manufacturers‘ Association, and

thus pedestrian protection measures have been required

on all passenger cars sold in Europe since 2005 [15].

The EEVC WG17 established a series of component

tests based on the three most important areas of injury:

head, upper leg, and lower leg. The EEVC WG17

developed this method for assessing the pedestrian

friendliness of a vehicle. The EEVC WG17 tests consist

of four models of pedestrian impactor models, namely

child headform, adult headform, upper-legform and

lower-legform impactors. Figure 13 illustrates the

pedestrian protection concept proposed by the EEVC

WG17 [16].



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Fig. 13 Pedestrian protection concept proposed by the

EEVC WG17 [16]

These EEVC WG17 regulations thus will be

completed and applied to vehicle manufacturing in

Europe. In India there is no such regulation for vehicle

manufacturing. The adult headform impactor is used to

test the points lying on boundaries described by a WAD

of 1500mm and the rear of the bonnet top, or a WAD of

2100mm for a long bonnet. Each section is divided into

three parts, as illustrated in Fig.14.

Fig. 14 Description of the impact area for pedestrian

headform- impactor-to-bonnet-top tests

In each part, a minimum of three tests is carryout at

spots with high injury risk. Test points should vary

according to the types of structure, which vary

throughout the assessment area. The selected test points

for the adult headform impactor should be a minimum

of 165mm apart, a minimum of 82.5mm inside the

defined bonnet side reference lines, and a minimum of

82.5mm forwards of the defined bonnet rear reference

line. The impact angle for tests with the adult headform

impactors must be 650

with respect to the ground

reference level. The initial impact velocity is 40 km/h

for the adult headform impactors. Distances (WADs)

(Fig. 15) of 1000mm and rear reference line. Each

selected test point for the child headform impactor

should also be a minimum of 130mm rearwards of the

bonnet leading-edge reference line. The impact angle for

tests with the adult headform impactors must be 650

respectively with respect to the ground reference level.

The initial impact velocity is 40 km/h for and the adult

headform impactors.

Fig. 15. Determination of WAD [16]

1.2 Finite element model and simulation

In Finite element the model of vehicle and adult

headform is crated. This study analyses the effect of the

bonnet skin and bonnet reinforcement thicknesses on

pedestrian head injury by performing headform

impactor simulations of the EEVC WG17 regulations

using different thicknesses. Figure 16(b) shows the

finite element models of adult headform impactors.

Fig. 16.The finite element model used in pedestrian –

head – bonnet impact simulations: (a) the passenger car

model [18]; (b) the headform impactor model [17]

The vinyl skin is modelled using viscoelastic

material, and a steel core with elastic material [17]. All

headform impactor parts use solid elements. The adult

headform impactor model consists of 3713 nodes and 13

783 solid elements. The adult headform impactors

satisfy the EEVC WG17 certification tests [17],

demonstrating the feasibility of their use in simulating

headform impactor tests. Bonnet-top simulations are

performed using the adult headform impactors

simulations of the headform-to-bonnet-top test are

performed using the finite element models of the

headform impactor mentioned above and a Ford Taurus

car model [18], as shown in Fig. 16 (a). In the engine

compartment, components that are close to the bonnet

top include the oil cap and the battery. This study does

not consider the effect of the engine compartment

arrangement on the head injury criterion (HIC) value.

Therefore, all parts in the engine compartment that are

close to the bonnet are moved down to ensure that the

bonnet does not impact any parts in the engine

compartment during simulation.



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IV. CONCLUSIONS

Both the methods give the optimal results to protect

the pedestrian safety. In both the methods the

Hypermesh and Ls-Dyna software are used. To protect

the pedestrian these systems must be implemented to all

the manufactures of automobile vehicles. This study

analyses and proposes a method of identifying the most

effective values for the bonnet reinforcement thickness

and the bonnet skin thicknesses to protect pedestrians

while maximizing the bonnet stiffness. The method

presented in this study uses the regression technique to

design constraints for the optimization problem. The

proposed algorithm identifies numerous critical

positions on the bonnet surface with respect to

pedestrian safety. The algorithm used to optimize the

thicknesses is solved by combining LS-DYNA and LS-

OPT to simulate and analyze the simulation results.

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comparative evaluation for pedestrian safety systems · comparative evaluation for pedestrian...

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