mrev high-deck bus rollover

7/28/2019 MRev High-Deck Bus Rollover

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Stability of High-Deck Bus in Rollover and

Contact-Impact with Traffic Barriers


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Stability of High-Deck Bus in Rollover and Contact-Impact with Traffic Barriers

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Disclaimer

The information contained in the report is restricted and/or privileged information and is intended

only for authorised screening and/or confidential presentation of MIROSs discretion. This report

should not be disseminated, modified, copied/plagiarised or action taken in reliance upon it,

unless permitted by MIROS. None of the materials provided in this report may be used,

reproduced or transmitted. In any form or by any means, electronic or mechanical, including

recording or used of any information storage and retrieval system, without written permission

from MIROS. Any conclusion and opinions in the report may be subject to reevaluation in the

event of any forthcoming additional information or investigations. MIROS declares that all the

inquiries which MIROS believes are necessary and appropriate and that nothing significance

which MIROS regards as relevant have, to MIROS knowledge, been withheld from the report.

(Source of pho tos on c over: RMP and Sin Chew Dai ly)


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Table of Contents

Pages

9 Acknowledgements

10 Abstract

11 1. Introduction

12 2. State of Current Local Bus Construction

12 2.1 Bus Construction and Regulations

12 2.1.1 Adoption of UNECE Regulations in Malaysia

15 2.1.2 Overview of UNECE Regulation 66

15 2.1.3 Overview of UNECE Regulation 107

17 2.1.4 Malaysias Road Transport Rules

18 3. Physics of Rollover

18 3.1 Stability Issue Determination of Centre of Gravity (CG)

18 3.1.1 Definition of Rollover

19 3.1.2 Factors of Rollover

22 3.1.3 Centre of Gravity Calculation

26 4. Longitudinal Traffic Barriers

28 4.1 Flexible Barrier Systems

28 4.1.1 General Description and Behaviour Under Impact31 4.1.2 Crash Test and Result

32 4.1.3 Advantages and Disadvantages

33 4.2 Semi-Rigid Barrier Systems

33 4.2.1 General Description and Behaviour Under Impact

35 4.2.2 Crash Tests and Results


37 4.3 Rigid Barrier Systems

37 4.3.1 General Description and Behaviour Under Impact38 4.3.2 Crash Tests and Results


43 5. Analysis of High-Deck Bus vs. Traffic Barrier Collision

43 5.1 Impact Severity Analysis

45 5.2 Rollover Analysis Bus-Traffic Barrier Collision


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45 5.2.1 Rollover on Straight Road

47 5.2.2 Rollover at Curve Road

48 5.2.3 Design of Vehicle

49 6. Conclusion49 7. Recommendations

49 7.1 Bus Construction

51 7.2 Traffic Safety Barrier Consideration

52 References


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List of Figures

Pages

13 Figure 2-1 Conventional frame for single-deck bus/coach13 Figure 2-2 Example of single-deck superstructure frame

19 Figure 3-1 Relationship between CG and rollover

20 Figure 3-2 Diagram of bus before pivoting

21 Figure 3-3 Critical point of rollover

22 Figure 3-4 Lateral component of vehicle moving with velocity () and angle ()23 Figure 3-5 Longitudinal position of CG

24 Figure 3-6 Transverse position of CG

24 Figure 3-7 Tilting test for determining the height of CG29 Figure 4-1 Cross section of two typical designs of wire rope barrier system

34 Figure 4-2 Profiles of semi-rigid safety barriers used on road shoulder and median

37 Figure 4-3 Profiles of rigid barriers

41 Figure 4-4 General profile of STEP barrier

43 Figure 5-1 Impact severity plot

45 Figure 5-2 Free Body Diagram (FBD) of bus turning moment

46 Figure 5-3 FBD of bus turning moment for collision with rigid barrier


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List of Plates

Pages

30 Plate 4-1 Flexible wire rope barrier at Kuala Lumpur-Karak Expressway (E8) in

Gombak

30 Plate 4-2 Flexible wire rope barrier on flyover at Middle Ring Road 2 (MRR2) in

Gombak

31 Plate 4-3 Flexible wire rope barrier on median at Second Link Expressway (E3)

near Perling toll plaza, Johor

34 Plate 4-4 Single-mounted W-beam guardrail median at North-South Expressway

(E2) in Serdang

35 Plate 4-5 Double-mounted W-beam guardrail median at Kepong road

35 Plate 4-6 Customized stacked mounted W-beam guardrail at Karak Expressway

(E8)

38 Plate 4-7 Concrete barrier at MRR2 in Selayang

38 Plate 4-8 Concrete barrier with antiglare screen at Karak Expressway (E8)


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List of Tables

Pages

25 Table 4-1 Test Level for Longitudinal Traffic Barrier

28 Table 4-2 Typical Severity Indices for Safety Barriers and Various Design Speeds

32 Table 4-3 Results for Deflections of Crash Tested Wire Rope Safety Barriers

36 Table 4-4 General Summary for Semi-Rigid Barriers Installation

41 Table 4-5 Crash Test Data Summary

43 Table 5-1 Results of Impact Severity Calculation Analysis

44 Table 5-2 Impact Severity Comparison

47 Table 5-3 Minimum Radius of a Curve


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List of Acronyms and Abbreviations Used

4WD Four-Wheel Drive

AA Average Acceleration

ADR Australian Design Rules

ARRB Australian Road Research Board

ASI Acceleration Severity Index

CG Centre of Gravity

CRASE Crash Safety Engineering Unit of MIROS

EN European Norm

FBD Free Body Diagram

FHWA Federal Highway Administration

(A division of the United States Department of Transportation)

IS Impact Severity

LLM Lembaga Lebuhraya Malaysia

MIROS Malaysian Institute of Road Safety Research

MOT Ministry of Transport

MRR2 Middle Ring Road 2

(Federal Route 28 which connects Kuala Lumpur and Selangor)

NCHRP National Cooperative Highway Research Program

(United States)

NHTSA National Highway Traffic Safety Association

(An agency of the Executive Branch of the United States Government

Department of Transportation)

OIV Occupant Impact Velocity

ORA Occupant Ridedown Acceleration

PCB Portable Concrete Barrier

PHD Post-Impact Head Deceleration

PRA Protectable Rollover Accident

PWD Public Works Department

(Jabatan Kerja Raya JKR)

R&R Rest and Recuperate

REAM Road Engineering Association of Malaysia


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RMP Royal Malaysian Police

(Polis Diraja Malaysia PDRM)

RSD Road Safety Department

(Jabatan Keselamatan Jalan Raya JKJR)RTD Road Transport Department

(Jabatan Pengangkutan Jalan JPJ)

SI Severity Index

SSF Static Stability Factor

THIV Theoretical Head Impact Velocity

TL Test Level

TRAPTER Transport Planning and Traffic Engineering Unit of MIROS

UNECE United Nations Economic Commission for EuropeUMTRI University of Michigan Transportation Research Institute

VSB Vehicle Safety and Biomechanics Research Centre of MIROS

WRSB Wire Rope Safety Barriers


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Acknowledgements

This study would not have been possible without the considerable support and cooperation of

many talented people, who have played a part, directly or indirectly, throughout its completion.

The authors would like to express their sincere gratitude to: (i) Road Transport Department

(RTD) of Malaysia and local coachbuilders for their cooperation in providing input related to the

local bus construction and regulation, and (ii) Malaysian Highway Authority (LLM) for their

assistance on traffic barrier matters. Special thanks are due to the following individuals for all

the help and advice to make completion of the study and its review report possible.

Malaysian Institute of Road Safety Research (MIROS)

Prof. Dr. Wong Shaw Voon Director General

Prof. Dr. Ahmad Farhan Mohd Sadullah Former Director General

Ir. Muhammad Marizwan Abdul Manan Unit Head TRAPTER

Crash Safety Engineering (CRASE) Unit

Publication and Knowledge Management Unit

Authors

Aqbal Hafeez Ariffin

Mohd Khairudin Rahman

Mohd Syazwan Solah

Khairil Anwar Abu Kassim


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Abstract

Despite the positive impact of high-deck buses for the operators by increasing their profits

through reduction of fuel consumption and vehicle operating maintenance as well as ability to

carry more passengers per trip compared to single-deck buses, the increasing popularity of the

high-deck buses in Malaysia has become a major concern in road safety. As a result of a fatal

accident involving a high-deck bus in Behrang (2008) which saw failure of median guardrail to

contain and redirect the errant bus on track, a feasibility study about the suitable traffic safety

barrier to be used on Malaysias expressways specifically for single vehicle collision involving

high-deck buses was initiated. The study was carried with two main objectives: (i) to analyze

stability of high-deck bus in rollover collision with crash barrier using calculation method based

on formulas derived in few related literatures, and (ii) to assess existing literatures for any type

of traffic safety barriers currently available worldwide for recommendation on adopting specific

crash barrier for high-deck buses to be used in Malaysias highways or roads. From the study, it

is concluded thatlocation of CG and speed influence stability of a high-deck bus during rollover

event, especially at curve road, and rigid barrier performs better than semi-rigid barrier in

preventing rollover of high-deck bus during collision with traffic barriers.


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1. Introduction

The use of high-deck buses as passenger vehicles for long-distance travel in Malaysia is

gaining popularity among coach operators. This trend of increasing usage of high-deck

buses by coach operators is most probably due to their capabilities of having more seats

(able to carry more passengers per trip) compared to the single-deck buses. In addition, by

shifting the operation from single to high-deck busses, coach operators can cut the cost of

fuel consumption and reduce vehicle operating maintenance, hence, increasing their profit.

However, there is a negative impact with this shift. If the high-deck bus is designed with full

headroom throughout both decks, there is a possibility for the bus to be top heavy and

become unstable (except with the use of counterweight system), thus unsafe for travelling.

This is a major concern in road safety since it can lead to serious high-deck bus accidents if

the use of this type of commercial vehicle kept on increasing, unless safety

countermeasures are considered and implemented.

The Malaysia Road Safety Department (RSD) formally requested the Malaysian Institute of

Road Safety Research (MIROS) to conduct a feasibility study on the suitable traffic safety

barrier to be used on Malaysias expressways specifically for single vehicle collision

involving high-deck buses. A team from the Vehicle Safety and Biomechanics (VSB)

Research Centre led by the Director took up the challenge to carry out the study which

focused on (i) overview of local bus construction including adaptation of United Nations

Economic Commission for Europe (UNECE) regulations, (ii) types of traffic barrier systems

currently available or used in Malaysias highways or roads, (iii) analysis of high-deck bus

collisions with crash barrier, and (iv) recommendations on adopting specific crash barrier for

high-deck buses.

This study was carried out as a preliminary literature research. All data gathered and used

to meet the objectives of this study was gained from related literatures, publications orreports since no actual crash test and research regarding high-deck bus collision with crash

barrier was performed, the crash test results for assessment of existing traffic safety barriers

included in this report might not cover all crash tests carried out worldwide. However, only

selected crash tests results were used for comparison purpose.


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2. Current State of Local Bus Construction

2.1 Bus Construction and Regulations

2.1.1 Adoption of UNECE Regulations in Malaysia

Conventional bus/coach structure manufacturing involves labour-intensive arc welding

of tube stock. In order to build the body of a bus, it must consist of five separate major

units: side, floor, roof, front and rear units. All of these units are constructed separately

and they will be joined together later during the final assembly. After the final structure

assembly, the frame is subjected to grit blasting and zinc phosphate coating. Most of

the structure joining processes is done using the arc weld method. Figure 2-1 shows

an example of a conventional frame for single-deck bus/coach.

In all vehicles studied, fractures at the welding connection took place after a given

period of service. This failure mechanism was identified as fatigue and it influenced the

structures integrity, especially when the bus was involved in a serious accident such

as a rollover.

Late in 2007, a bus accident occurred in Bukit Gantang, Perak and killed 23 people

onboard. Since that incident, the Malaysian government reinforced the bus

construction law to protect customers and coach builders. Adaptation of UNECE

Regulation 66 Uniform Technical Prescriptions Concerning the Approval of

Large Passenger Vehicles With Regard To the Strength of Their Superstructure

into Malaysias Road Transport Rule was done and the new regulation was enforced

by the Road Transport Department (RTD). However, a grace period was given to

coach builders to implement the rules so as to avoid sudden burden to the coach

builders.

In Malaysia, there are a large number of coach builders and they are moving towards

that to make sure their market can be expanded not only in Malaysia but also to other

countries. As of to date, many of the coach builders had already implemented the

UNECE R66 in their bus or coach body construction practice. The regulation basically


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focuses on the body frames integrity and durability. The main frame itself must be built

with a continuous transversal frame to sustain it in a rollover impact as shown in

Figure 2-2.

Apart from that, the regulation also highlights the method to verify the bus or coach

structure. However, the method to verify the bus or coach structure is not valid for

high-deck buses.

There is a another UNECE regulation that states the special requirement for double-

deck vehicle, which is the UNECE Regulation 107 Uniform Provisions

Concerning the Approval of Double-deck Large Passenger Vehicle With Regard

To Their General Construction. However, there is no specific requirement stated inthe regulation to verify the integrity of the double-deck super structure.

Figure 2-1 Conventional frame for single-deck bus/coach

(Sou rce: F. Lan et al., 2004)

Non-continuous

transversal frame


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Figure 2-2 Example of single-deck superstructure frame

(Sou rce: E. Lar rodet al., 1995)


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2.1.2 Overview of UNECE Regulation 66

The UNECE R66 was initiated to prevent severe damage on buses, thus ensuring the

safety of bus passengers, via mitigation of injuries sustained, in the case of rollover.By definition, superstructure refers to the components of a bus structure that contribute

to the strength of the vehicle in the event of a rollover. Ultimately, an UNECE R66

approved bus is supposed to be able to withstand impact from rollover accident such

that the residual space is intact during and after the accident. In other words, intrusion

to residual space with luggage should not happen and no parts from the residual

space should be projected outside in the event of a rollover.

There are few equivalent methods for approval test other than rollover test on acomplete vehicle. It is also acceptable to carry out the rollover or quasi-static test on

body sections which are representative of the complete vehicle. Other equivalent tests

are quasi-static calculations based on the results of component tests and computer

simulation via dynamic calculations.

Currently, the existing UNECE R66 regulation relates only to large, single-deck buses.

Double-deck buses are excluded from it. There is no regulation for the strength of

superstructure for double-decker coaches.

High-deck buses are also not well represented in the UNECE R66 regulation. The

existing approval test is not specifically tailored for it even though some modifications

of the test can be done to better suit high-deck buses. The main problem is that the

approval test does not appropriately separate the weak superstructure from the strong

one (UNECE R66, 2006).

2.1.3 Overview of UNECE R107 Regulation

The following is an overview of R107 Uniform Provisions Concerning the

Approval of Double-deck Large Passenger Vehicles with Regards to Their

General Construction Annex 9.


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The regulation applies to every type of single-deck bus, double-deck bus, rigid

or articulated vehicle in category M2 (vehicles used for the carriage of

passengers, comprising more than eight seats in addition to the driver's seat,

and having a maximum mass not exceeding five tonnes) and M3 (vehiclesused for the carriage of passengers, comprising more than eight seats in

addition to the driver's seat, and having a maximum mass exceeding five

tonnes).

The requirement is an additional regulation for double-deck buses. However,

Annex 3 shall apply to double-deck vehicles if there is no regulation that is not

stated in this requirement.

Annex 9 encloses the special requirements for double-deck vehicle. The

abstract requirements are : Total load of vehicle should be in running order. The load of passengers

shall be placed on each upper deck passenger seat. If the vehicle is

intended to be used with a crew member who is not seated, the centre of

gravity (CG) of the mass of 75kg representing the crew member shall be

placed in the upper deck gangway at a height of 875mm. The baggage

compartments shall not contain any baggage.

Fire extinguishers and first aid equipment shall be provided at two places,

one near the driver and one on the upper deck. The number of exits (including service and emergency required for

double-deck bus) depends on the number of passengers and crew

onboard. Technical requirements of each door are stated.

The design of intercommunication staircases as an access way (between

lower and upper deck) shall not be endangering of passengers being

projected downwards during heavy braking. This requirement is

considered to be fulfilled if at least one of the following conditions is met:

No part of the staircase is forward descending; The staircase is equipped with guards or a similar provision;

There is an automatic device in the upper part of the staircase which

prevents the use of the staircase when the vehicle is in motion; this

device shall be easily operable in an emergency.


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Handrails or/and handhold for inter communications staircases shall be

provided at each side including a grasping point available to a person

standing on the lower and upper deck adjacent to the inter

communication staircase. The requirement for seating position for lower and upper deck states that

each seat shall have a free height of not less than 900mm measured from

the highest point of the uncompressed seat cushion. This free height shall

extend over the vertical projection of the whole area of the seat and the

associated foot space. In the case of the upper deck, this free height may

be reduced to 850 mm.

The maximum emergency doors' steps are 850mm for lower deck and

1500mm for upper deck. The gangways condition is different from a single-deck vehicle. The

gauging device is designed for upper deck to fulfil the requirement.

2.1.4 Malaysias Road Transport Rules (Compilation of 46 Rules, version 25th February

2008)

Stability test for high-deck vehicle is also stated in Motor Vehicle Rules (Construction

and Use 1959). The mass of the driver and passengers can be replaced by other

elements equivalent to represent the mass of the upper deck compartment. The

vehicle shall be tilted without rocking and without dynamic effects until it reaches

unstable equilibrium and commences its rollover. The maximum angle of tilt is 28

degrees and the vehicle shall fail if it rolls over before reaching the maximum angle.

Other requirements stated in the rules for high-deck vehicle focus on the construction

of the vehicle itself.


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3. Physics of Rollover

3.1 Stability Issue Determination of Centre of Gravity (CG)

3.1.1 Definition of Rollover

It is apparent that UNECE R66 is focusing on the ability of a vehicle to sustain its

residual space after a rollover crash. Rollover crash is by far the worst scenario

possible for a vehicle to undergo because the resulting damage could be very

extreme, as compared to other types of crashes such as head-on and side collisions.

Due to the rollover crashs nature, all bus occupants have a higher possibility to

sustain serious to fatal injury when the vehicle is toppling upside down. At that point of

time, structure of the roof is vulnerable to intrusion and projection.

Rollover causes can be generally divided into two main categories; tripped and

untripped (Deshmukh, 2006). A tripped rollover is caused by an object that a vehicles

tires comes in contact with, abruptly stopping the lateral motion of the tire and sending

it to roll around that object. Examples of tripping objects are curbs, ramps, rocks, and

soil. Untripped rollover usually occurs because of severe steering manoeuvres such as

J-hooks, lane changes, and fast turns.

Matolcsy (2003), in his analysis of rollover cases throughout Europe, suggested that

rollovers can be categorized into different groups based on a few characteristics.

Mostly, the characteristics lie around the number of rotations experienced by a vehicle

during the rollover event. For example, turn on side equals rotation. Turn into a ditch

is between and rotation, and rollover from the road is between to two full

rotations. These three types of rollovers fall into the Protectable Rollover Accidents

(PRA) category, a kind of rollover accident that when the bus occupants are involved,

they have a high probability of survival. Other kind of rollovers are serious rollover

(more than two rotations), and combined rollover, a rollover followed by a fire, fall into

a lake, etc.


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3.1.2 Factors of Rollover

There are a few factors that can influence the probability of the occurrence of a

rollover. These include position of the vehicles CG, vehicle speed, angle of impactupon collision with barrier, and barrier as tripped factor. The first three factors are

explained in this section while in-depth details about barrier are explained in the next

section.

a) Centre of Gravity

Rollover of a vehicle is directly related to its CG in the sense that a vehicle is

unlikely to rollover if its CG is in the region of gravitational patch, viewed from the

top. The CG is always balanced within the gravitational geometry of some supportstructure. For this case, it is initially formed by the tires. A vehicle rolls over

because its CG is no longer balanced within the gravitational geometry formed by

the tires. It is now being contained by another support structure, which is the

offside of the bus.

Figure 3-1 Relationship between CG and rollover (Illustrated with gravitational

patch)


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In Figure 3-1, the vehicle on the left is on level ground. From the top, the CG is

contained within the gravitational support structure (formed by tires). Therefore

rollover will not happen, according to the basic laws of physics.

The vehicle on the right is bus cambering to the driver side. From the top, the CG

has moved outside the gravitational support structure. Therefore, rollover will

occur.

b) Speed

Rollover occurs when a vehicle is moving or sliding sideways until it strikes a solid

object such as a curb. The curb provides a pivot point for the vehicle to rotate. The

figures below show more details on rollover physics.

Figure 3-2 Diagram of bus before pivoting

Figure 3-2 shows a vehicle with height of CG, and track width, is movingsideways with lateral velocity, . The vehicle is about to trip at the pivot point,which is represented by the curb.

CG


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Figure 3-3 Critical point of rollover

At this point, the vehicle is at the critical point for rollover. The critical point is

achieved when the CG is at the maximum height. According to Pythagoras

Theorem, at the maximum CG height, equals the hypotenuse of a right angle withsides and .

r = (Equation 1)

Energy conservation requires that kinetic energy (lateral) before pivoting equals

potential energy at the critical point. The end result yields a formula of critical

speed, ,

( ) (Equation 2)where

The value ofor widely known as Static Stability Factor (SSF) is adopted byNational Highway Traffic Safety Administration (NHTSA) as the parameter for

rollover tendency.

c) Angle of Impact

For a vehicle to rollover as a result of sliding sideways, there shall be lateral

movement of the vehicle. In a real-life rollover crash, vehicle approaches pivot

point (curb, barrier, or solid object) at a certain angle. The magnitude of the angle

can influence whether or not rollover will occur as illustrated in the figure below.

CG


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Figure 3-4 Lateral component of vehicle moving with velocity () and angle ()

Using trigonometry theorem, the lateral speed of the bus can be calculated by the

following equation.

(Equation 3)The theorem proves that a narrow angle of impact will certainly lower the

likelihood of rollover from occurring. This is because the lateral component of the

vehicles speed is less as the angle of impact decreases.

3.1.3 Centre of Gravity Calculation

A rollover accident is directly related to the CG of the vehicle. To determine the

position of the CG of a bus, three parameters need to be defined; the longitudinal

distance ( ) from the centre line of gravity, the transverse distance ( ) from thevertical longitudinal central plane of the vehicle, and the vertical height () above theflat horizontal ground level when the tires are inflated. The CG can be calculated with

or without considering the effect of the total occupant mass.

The transverse position () of the vehicles CG needs to be determined first in order tofind the vertical height ( ) of the CG. Furthermore, the bus needs to be tiltedlongitudinally to find the load cells at the wheels of two axles while tilting.


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The following formulas to determine the CG of a bus are derived from UNECE R66

regulation.

Figure 3-5 Longitudinal position of CG

(Sour ce: UNECE R66, 2006)

The longitudinal position () of the CG relative to the centre of the contact point of thefront wheels (Figure 3-5) is given by,

(Equation 4)

where:

P1 = reaction load on the load cell under the left-hand wheel of the first axle,

P2= reaction load on the load cell under the right-hand wheel of the first axle,

P3 = reaction load on the load cell under the left-hand wheel(s) of the second axle,

P4= reaction load on the load cell under the right-hand wheel(s) of the second axle,

P5= reaction load on the load cell under the left-hand wheel(s) of the second axle,

P6= reaction load on the load cell under the right-hand wheel(s) of the second axle,

Ptotal= P1+P2+P3+P4+P5+P6 = Mkunladen kerb mass; or,

= Mttotal effective mass,

L1 = wheelbase distance from 1st

axle to 2nd

axle, andL2= wheelbase distance from 2

nd axle to 3rd axle, if fitted.


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Figure 3-6 Transverse position of CG

(Sou rce: UNECE R66, 2006)

The second parameter, which is the transverse position (t) of the CG relative to its

longitudinal vertical centre plane as shown in Figure 3-6 is given by,

(Equation 5)

where:

T1 = track width of 1st axle,

T2= track width of 2nd axle, and

T3 = track width of 3rd axle.

Bear in mind that the CG is situated to the right of the centre line of the bus if the

value of

is negative and it goes the other way around if the value is positive.

Figure 3-7 Tilting test for determining the height of CG

(Sour ce: UNECE R66, 2006)


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Finally, the third parameter of the CG, the vertical height shall be determined by tilting

the vehicle longitudinally and using individual load-cells at the wheels of two axles.

ReferFigure 3-7 for more comprehension.

In determining the vertical height (), more accurate calculation shall be obtained ifthe angle is greater. Initially, the inclination of the tilting test shall be determined by

the equation

(Equation 6)

Where H is the height difference between the footprints of the wheels of the 1 st and

2nd axles and is the wheelbase distance between 1st and 2nd axles.Next, the unladen kerb mass of the bus shall be checked as follows:

(Equation 7)where:

F1= reaction load on the load cell under the left hand wheel of the 1st axle,

F2= reaction load on the load cell under the right hand wheel of the 1st axle,

F3 = reaction load on the load cell under the left hand wheel of the 2nd axle, and

F4 = reaction load on the load cell under the right hand wheel of the 2 nd axle.

Then, the angle measured from inclination test and the resultant loads shall be used

in the vertical height calculation of the CG, which is given by:

(Equation 8)

where is the height of wheel centre (on first axle) above the load cell top surface.


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4. Longitudinal Traffic Barriers

Currently, there are three distinct longitudinal safety traffic barriers (flexible, semi-rigid and

rigid) being used on the roads and expressways in Malaysia. The following sections

describe a number of typical traffic safety barriers but the list does not contain data of all

available barrier systems.

These existing traffic barriers had been adopted by the Malaysian Public Works Department

(PWD) of Malaysia based on the test results of performance evaluation for road safety

features carried out by the National Cooperative Highway Research Program (NCHRP)

Report 350, published in 1993.

The report provides guidelines on the recommended testing procedure for the performance

evaluation of various highway safety features. There are six Test Levels (TL) recommended

in the guidelines and the summary of descriptions (including the impact severity) are shown

in the table below.


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Table 4-1 Test Level for Longitudinal Traffic Barrier

(Source: Main Ro ads Western A ustral ia, 2006)

Test

Level

Test Vehicle Test

Speed

(km/h)

Impact

Angle

(degrees)

Height of

Centre of

Gravity

(mm)

Impact

Severity

(kJ)Mass (kg) Type

1820 Small car 50 20 550 9.3

2000 *4WD/utility truck 50 25 700 34.5

2820 Small car 70 20 550 18.1

2000 *4WD/utility truck 70 25 700 67.5

3820 Small car 100 20 550 37.0

2000 *4WD/utility truck 100 25 700 137.8

4820 Small car 100 20 550 37.0

2000 Single-unit van truck 80 15 1250 132.3

5820 Small car 100 20 550 37.0

36000 Van type semi-trailer 80 15 1850 595.4

6

820 Small car 100 20 550 37.0

36000Tanker type semi-

trailer80 15 2050 595.4

*Four wheel drive

As shown in Table 4-1 above, the Impact Severity (IS) is used as a basis to compare the

test levels and is calculated based on the principle of kinetic energy (Main Roads Western

Australia, 2006). The formula is given by,

[] (Equation 9)

where

impact severity (kJ),

mass of vehicle (kg),

vehicle velocity (m/s) and

impact angle (degrees).Other than the calculated impact severity, assessment of Occupant Impact Velocity (OIV)

and Occupant Ridedown Acceleration (ORA) are also required as the main requirements for

the test to assess the occupants injury risk (Groe et al., 2004).


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In order to measure the expected severity outcome of an impact with an object, the Severity

Index (SI) is used. The index is described by a value between 0 to 10, with the lowest value

(0) representing an expected crash involving no property damage or injury, while the highest

value (10) represents an expected crash with a 100% probability of a fatality (Main RoadsWestern Australia, 2006). Table 4-2 shows the expected severity indices for safety barriers

for all vehicles at varying speeds.

Table 4-2 Typical Severity Indices for Safety Barriers and Various Design Speeds

(Source: Main Roads West ern Aus tral ia, 2006)

Safety BarriersDesign Speeds (km/h)

70 80 90 100

4 wire rope (flexible) 1.5 2.0 2.5W-beam (*G4) 2.0 2.5 3.0

Thrie-beam 2.0 2.5 3.0

Type F (concrete) 2.0 2.5 3.5*Blocked-out Strong Post

4.1 Flexible Barrier Systems

4.1.1 General Description and Behaviour Under Impact (Sources: Australian Road

Research Board (ARRB) Transport Research, n.d.; Main Roads Western Australia,

2006; Road Engineering Association of Malaysia (REAM), 2006)

Wire Rope Safety Barriers (WRSB) or also known as Wire Rope Safety Fences, are

classified as flexible barrier systems which create large deflections when impacted by

vehicles. Because of this unique characteristic, the flexible wire rope barriers cause

the least damage and the smallest injury risk to the vehicles and occupants

respectively, as compared to other existing barrier types. There are two types of

flexible barrier systems, namely vertical array and twisted array wire rope safety

fences. The latter is the commonly used type of flexible barrier in Malaysia.

Generally, the barrier comprises three or four tensioned galvanized steel wire ropes

suspended by frangible posts at varying heights between 690mm to 710mm and at an

interval of 2.4 or 3.2 meter each along the barrier. The upper ropes which consist of


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one or two wire ropes are located in a slot on top of the post at a height of 600mm

10mm from the ground. The other two lower ropes are normally located on rollers or

wire rope, hung at a height of 500mm 10mm from the ground, and interwoven

between each pair of line and deflection posts. Figure 4-2 shows the general

arrangement of the barrier system installation.

Twisted Array Vertical Array

Figure 4-1 Cross section for two typical designs of wire rope barrier system

(Source: ARRB Transpo rt Research , n.d.)

Currently, there are two types of wire rope safety barrier systems used in Malaysia: 1.Wire rope barrier system with double curve shaped posts, and 2. Wire rope barrier

system with circular posts. The following plates (4-1, 4-2 and 4-3) show the typical

installation of this type of barrier on Malaysian roads.


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Plate 4-1 Flexible wire rope barrier at Kuala Lumpur-Karak Expressway (E8) in Gombak

Plate 4-2 Flexible wire rope barrier on flyover at Middle Ring Road 2 (MRR2) in Gombak


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Plate 4-3 Flexible wire rope barrier on median at Second Link Expressway (E3) near

Perling toll plaza, Johor

4.1.2 Crash Test and Result

Prior to installation, the barrier system should be crash tested according to the United

States (US) NCHRP Report 350 (1993) testing conditions by the Federal Highway

Administration (FHWA) or any procedures recognized internationally. Descriptions of

requirement for the crash test and result (REAM, 2006) are as below.

US Test Level: Complies with TL-3

Deflection: Varies with type of barrier (Typically 1.7 to 3.4m for a

2000kg vehicle at 100km/h impact speed and 25

approach angle)

Offset from obstruction approximately 1.7m and 1.0m

for 2.4m and 1.0m post spacing, respectively

Passenger Injury Risk: OIV of maximum speed of 12m/s (43.2km/h)

ORA of 20g (maximum)


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The following table shows some of the results of the test carried out on a 4 wire rope

safety barrier system.

Table 4-3 Results for Deflections of Crash Tested Wire Rope Safety Barriers

(Source: REA M, 2006)

Anchor

Spacing

(m)

Post

Spacing

(m)

Vehicle

Mass (kg)

Speed

(km/h)

Impact

Angle

(deg)

Impact

Severity

(kJ)

Measured

Deflection

(m)

1 319.2 1.0 753 113 20 43.4 0.86

2 100.8 3.2 875 104 19 38.3 1.00

3 103.2 2.4 1260 83 30 83.7 1.20

4 319.2 1.0 1480 115 20 88.3 1.00

5 100.8 3.2 1492 111 19 75.6 1.40

6 626.4 2.4 1500 113 20 86.4 1.70

7 106.1 3.2 1505 115 20 90.0 1.73

8 192.0 2.4 2010 102 25 144.1 1.65

From the results shown in the Table 4-3 above, it can be generally concluded that anincrease in the post spacing increases the deflection length of the barrier system.

4.1.3 Advantages and Disadvantages (Sources: Main Roads Western Australia, 2006;

Monash University Accident Research Centre (MUARC), 2006; REAM, 2006;

Federation of European Motorcyclists Associations (FEMA), 2000)

Although the flexible barrier system has relatively large deflections, greater clearanceshould be provided for installation within medians. It should not be installed in median

of width less than 2.5m. In addition, the system should not be used on a vertical sag

curve of radius less than 3000m as well as on a horizontal curve of less than 200m. In

addition, flexible wire rope safety barrier should not be installed and connected directly

to other barriers of bridge parapets since its deflection cannot be safely guaranteed if


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vehicles collided in the transition area between the flexible barrier and other barrier

systems.

If the wire rope system is properly installed according to guidelines, it is capable ofredirecting the errant vehicles smoothly when impacted by vehicles. Snagging effect is

minimized during impact since its unique design enables the cables to strip from the

collapsible posts.

Last but not least, the maintenance costs associated with repairing the damaged

barrier are minimal; hence the rope barrier system provides significant cost advantage.

4.2 Semi-Rigid Barrier Systems

4.2.1 General Description and Behaviour Under Impact (Sources: Main Roads Western

Australia, 2006; REAM, 2006)

There are three types of semi-rigid safety barriers commonly used on Malaysian roads

which are the W-beam, Thrie-beam, and Modified Thrie-beam guardrails. The barrier

system deforms significantly but not excessively (greater deflection propertiescompared to the rigid system, but less than the flexible system) when impacted by

vehicles and has a moderate deflection of a maximum of 1.2m. It can be categorized

into two groups. The first one, which is the strong beam with weak post, is purposely

designed to break away so that the impact force is distributed by the beam action to a

relatively large number of posts. In contrast, the strong beam with strong post is

purposely designed to only deflect moderately and the impact force is distributed by

beam action to a smaller number of posts.

The system mainly includes a steel beam attached to block out units supported on

posts. The block out units and posts are normally constructed of steel. Although there

are posts constructed of wood and concrete, they are not favoured because of poor

impact performance. The profiles for each type of semi-rigid barriers typically installed

on road shoulder are shown below in Figure 4-2.


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Figure 4-2 Profiles of semi-rigid safety barriers used on road shoulder and median

(Source: Main Roads Western A ustral ia, 2006)

The following plates illustrate the various types of semi-rigid barriers installed in

Malaysia.

Plate 4-4 Single-mounted W-beam guardrail median at North-South Expressway (E2) in

Serdang


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Plate 4-5 Double-mounted W-beam guardrail median at Kepong road

Plate 4-6 Customized stacked mounted W-beam guardrail at Karak Expressway (E8)

4.2.2 Crash Tests and Results

Similar to flexible barrier system, NCHRP Report 350 is adopted by the Malaysian

government for the guidelines of standard crash test procedure to evaluate the safety

performance for semi rigid barrier system to be used in Malaysia. Details of the semi-

rigid barrier installation and test results are as shown in the following table.


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Table 4-4 General Summary for Semi-Rigid Barriers Installation

(Source: REAM, 2006)

ON MEDIAN ON SHOULDER

MB4SBlocked-Out

W-Beam (SteelPost)

Blocked-OutThrie Beam

Modified Thriebeam

MB4SBlocked-Out

W-Beam(Steel

Beam) with2.0 Spacing

MB4SBlocked-Out W-Beam(Steel

Beam) with4.0 Spacing

Blocked-Out Thrie

Beam

ModifiedThrieBeam

TEST RESULTS:

Test Level 3 3 4 3 3 3 4

MaximumDeflection

0.6m 0.9m 0.5m 1.0m 1.2m 0.6m 0.9m

Passenger InjuryRisk

No detailed information

DESCRIPTIONS:

BeamDouble W-

beamsDouble Thrie-

beams2 Thrie-beams Single W-beam Single Thrie-beam

Post Spacing 2.0m 4.0m 2.0m

PostC Section

150 x 76 x 6mm

C Section150 x 110 x 6 mm



Off Set Brackets2 C Sections150 x 76 x 6

mm

2 C Sections150 x 110 x 6

mm

2 C Sections350 x 110 x 6

mm

1 C Section150 x 76 x 6 mm

1 C Section150 x 110 x 6 mm

Mountings 16mm dia. Steel Bolts

Footing None (Except at points of transition)

Median Width 2.5m min


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4.3 Rigid Barrier Systems

4.3.1 General Description and Behaviour Under Impact

A concrete barrier is classified as rigid safety barrier that does not deflect upon impact.

Generally, it is designed to contain and redirect errant vehicles upon impact. Even

though the barrier system is able to redirect the colliding vehicle stably without any

rolling movement, the severity of impact experienced by the vehicle is higher

compared to semi-rigid or flexible barrier. The rigid barrier can be classified into two

categories which are single slope (e.g. Texas Constant Slope Barrier and Californian

Single Slope Barrier) and multi slopes barrier (e.g. New Jersey Barrier and F-Type

Concrete Barrier). The figure below illustrates the profiles of some of the rigid concretebarriers currently available.

New Jersey Profile F-Type Profile Single Slope ProfileVertical Wall

Profile

*Note: All dimensions are in millimetres

Figure 4-3 Profiles of rigid barriers

(Sources: A RRB Transpo rt Research, n.d.; Main Roads Western Au stral ia, 2006)

As shown in the subsequent plates are the typical rigid barrier systems installation in

Malaysia.


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Plate 4-7 Concrete barrier at MRR2 in Selayang

Plate 4-8 Concrete barrier with antiglare screen at Karak Expressway (E8)

4.3.2 Crash Tests and Results

The concrete barriers are rigid and normally, they do not result into permanent

deflection (if properly installed according to specification) when impacted by vehicles. If

the height of the barrier is reduced to less than 725mm by pavement overlays,


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impacting vehicles may roll over the barrier (REAM, 2006). Crash tests for concrete

barriers need to comply with the NCHRP requirements or other internationally

recognized testing procedures (i.e. European Norm EN 1317). The followings describe

results for some of the crash tests carried out on various rigid concrete barriers.

a) New Jersey Profile Barrier (1270mm Portable Concrete Barrier (PCB))

Test performed by Office of Research & Development, Ohio Department of

Transportation (Report date: June 2006)

Barrier Data: Height of 457.2mm more than the standard 32-inch New

Jersey PCB

Slope of 3 degrees steeper than typical New Jersey shape(from first break point to top of barrier)

Joint connection each section is connected with a single pin

passing through 3 set of loops at each segment end


Test Date: No detailed information

Test

Description:

2000kg pickup truck at 100km/h with impact angle of 25

(NCHRP Report 350 Test 3-11)

Deflection: Nil

Passenger

Injury Risk:

OIV of 4.5m/s (longitudinal) and 6.1m/s (lateral)

ORA of -5.4m/s (longitudinal) and -8.6m/s (lateral)

b) Standard F-Type Precast Concrete Barrier

Test performed by Oregon Department of Transportation (Report date:

December 2001)

Barrier Data: 810mm in height; width of 610mm (base) and 240mm (top)

Barrier section length of 3810mm (each section is held

together with an assembly of pin and steel bar loops)

Each section is anchored with 2 galvanized pins (25mm

diameter and 750mm long), 50mm deep into the asphalt

(Refer report for more detailed specification)


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Test Date: 17 April 2001

Test

Description:

2000kg pickup truck at 100km/h with impact angle of 25

(NCHRP Report 350 Test 3-11)Deflection: 760mm max. barrier deflection (No NCHRP requirement,

Oregon Department of Transportations requirement

914mm)

Passenger

Injury Risk:

OIV of 0.0m/s (longitudinal) and -5.85m/s (lateral)

ORA of -18.23m/s (longitudinal) and -12.52m/s (lateral)

c) Single Slope Barrier (Texas Constant Slope Type 60G, 9.1 slope)

Test performed by FHWA (Acceptance letter: February 1998)

Barrier Data: Slip-formed and reinforced

1420mm in height; width of 610mm (base) and 150mm (top)

Footings 3050mm (length) x 250mm (depth) footing on both

ends with additional reinforcing steel, anchored in asphalt

while the middle section stands freely on the asphalt


Test Date: 28 November 1995

Test

Description:

2000kg pickup truck at 97.7km/h speed with impact angle of

25.5

Deflection: No information

Passenger

Injury Risk:

OIV of 6.80m/s (longitudinal) and -9.51m/s (lateral)

ORA of -6.7g (longitudinal) and 2.3g (lateral)

d) Concrete STEP Barriers (from the Netherlands & Germany) (Source: Groe

et al., 2004)

The system is a combination of the New Jersey shape and single slope

barrier. Generally, the base of the barrier is wider than the single slope

barrier; although the height is more (with narrow width) than the New Jersey

barrier. The general profile of the STEP barrier is shown in Figure 4-4 below.


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(Note: 9 gon = 8.1 degree)

Figure 4-4 General profile of STEP barrier

(Source:Groe et al ., 2004)

The crash tests were performed according to the European Norm EN 1317 respectively

prEN 1317 and the summary of the results are shown in the following table.

Table 4-5 Crash Test Data Summary

(Note: Theoretical Head Impact Velocity, THIV OIV; Post-impact Head Deceleration, PHD ORA; Acceleration

Severity Index, ASI Max. 50ms Average Acceleration, AA)

(Sourc e: Groe et al ., 2004)


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4.3.3 Advantages and Disadvantages (Sources: Main Roads Western Australia, 2006;

MUARC, 2006; REAM, 2006; Groe et al., 2004)

One of the primary advantages of the rigid barrier system is its ability to preventvehicles (especially small cars) from the risk of rollover, hence avoiding big damages

due to rollover. The F-shape, the New Jersey profile, the single slope and the STEP

barrier (as only the vehicle tires will touch the barrier is slight collision occurs) are

among the rigid barriers which have this unique characteristic. In comparison

excluding the single slope and the STEP barrier, the F-shape performs better than the

New Jersey profile barrier in reducing the tendency for vehicles to roll. However, not all

rigid barriers perform better for all type of vehicles in reducing the risk of vehicle

rollover. For this case, the vertical concrete wall only performs better for heavyvehicles except for small cars and pickup trucks with mass of less than 2000kg or

motorcycles. The wall does not have the energy management feature of vehicle lifting.

Another advantage of the rigid barrier system, especially for the vertical concrete wall

and the single slope barrier (California and Texas profile), is that resurfacing would be

possible several times (255mm overlay until height is reduced to 815mm) without

affecting its performance.

On the contrary, the disadvantage of the rigid barrier system is that it will result in

severe collision if impacted by a vehicle with an impact angle of greater or equal to 20

degrees. Hence, it will cause severe injuries to vehicle occupants and extensive

damage to impacting vehicles. Compared to other rigid barriers, the single slope will

result in greater vehicle damages if impacted at shallow impact angles. In addition,

some rigid barriers have poor safety values and permanent delfection of more than

zero (0). Both California and Texas profile slope barriers have poor safety values, even

though the California (9.1 degree slope) has better result than the Texas (10.8 degree

slope). The precast concrete barrier (not suitable to be installed on median) and both

pre-fabricated H2 and slip-form H4b STEP barriers are the type of rigid barriers which

have permanent deflection as mentioned earlier.


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5. Analysis of High-Deck Bus vs. Traffic Barrier Collision

5.1 Impact Severity Analysis

A simple calculation analysis has been carried out using the formula in Equation 9to

compute the Impact Severity (IS) of high-deck bus collision with safety barrier, with

different impact angles and velocities. An approximate maximum load of 24350kg for

standard double-axles high-deck bus similar to the bus in the Behrang case as

mentioned earlier was used for this analysis. The results are shown in Table 5-1.

Table 5-1 Results of Impact Severity Calculation Analysis

Energy (kJ)Impact Angles (degree)

5 10 15 20 25 30 35 40 45

Velocity(km/h)

10 0.7 2.8 6.3 11.0 16.8 23.5 30.9 38.8 47.020 2.9 11.3 25.2 44.0 67.1 94.0 123.7 155.3 187.930 6.4 25.5 56.7 98.9 151.0 211.4 278.2 349.4 422.840 11.4 45.3 100.7 175.9 268.5 375.9 494.6 621.2 751.750 17.8 70.8 157.4 274.8 419.6 587.3 772.8 970.6 1,174.560 25.7 102.0 226.6 395.7 604.2 845.7 1,112.9 1,397.6 1,691.370 35.0 138.8 308.4 538.6 822.4 1,151.1 1,514.7 1,902.3 2,302.180 45.7 181.3 402.9 703.5 1,074.1 1,503.4 1,978.4 2,484.7 3,006.890 57.8 229.5 509.9 890.3 1,359.4 1,902.8 2,504.0 3,144.7 3,805.5

100 71.4 283.3 629.5 1,099.2 1,678.3 2,349.1 3,091.3 3,882.3 4,698.1110 86.4 342.8 761.6 1,330.0 2,030.7 2,842.4 3,740.5 4,697.6 5,684.7120 102.8 408.0 906.4 1,582.8 2,416.7 3,382.7 4,451.5 5,590.6 6,765.3

Figure 5-1 Impact severity plot


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Based on the results above, it can be concluded that as the values of the impact angle

and velocity increases, IS increases. The IS, which is based on the principle of kinetic

energy, increases exponentially and is directly proportional to the square of vehicles

speed. Furthermore, the significant change is more eminent for higher impact angle asillustrated in the Figure 5-1.

Another analysis was carried out to compare the results of IS from the above calculation

with the test results of the NCHRP 350. The values of IS from the NCHRP 350 were then

used to find the range of calculated IS for high-deck bus collision with safety barriers.

From there, the range of speed was determined as shown in Table 5-2.

Table 5-2 Impact Severity Comparison

NCHRP 350 TestRequirements

Impact Severity Analysis for High-deck Bus Collision

Test Level IS(kJ) Impact Angle Calculated IS (kJ) Range Speed (km/h)

3 137.8 25 67.1 151.0 20 304 132.3 15 100.7 157.4 40 505 595.4 15 509.9 629.5 90 1006 595.4 15 509.9 629.5 90 100

From the comparison, it can be assumed that if a high-deck bus impacted the TL-3

barrier (presumed to be equivalent to W-beam guardrail) at an angle of 25, the range of

speed between 20 to 30km/h was needed to achieve the IS value of 137.8kJ obtained

from the NCHRP 350 test. The range of speed between 90 to 100km/h is required by a

high-deck bus to achieve the IS value of 595.4kJ if it was to collide with the TL-5/6

barrier (which is equivalent to concrete barrier) at a 15 angle. Hence, from the

comparison analysis:

The possibility of a high-deck bus to penetrate the TL-3 barrier is high for

travelling speed of more than 30km/h at a given angle of 25.

Similarly, the risk of a high-deck bus to penetrate the TL-5/6 barrier is high for

travelling speed of more than 100km/h at a given angle of 15.

However, it is to be noted that these assumptions were based solely on the calculation

analysis of impact severity from the formula in Equation 5that does not consider the

dimensions of the test vehicle, as well as differences in the height of the CG and bumper.


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5.2 Rollover Analysis Bus-Traffic Barrier Collision

A rollover analysis was performed to study the effect of increasing the CG of a high-deck

bus in relation to the height of the crash barrier. Different worst-case high-deck busrollover scenarios at straight and curve roads were explored for this section.

5.2.1 Rollover on Straight Road

According to Matolcsy (2007), the turning moment (M), as described in Figure 5-2, is a

main factor contributing to the initiation of rollover accidents on straight roads.

Figure 5-2 Free Body Diagram (FBD) of bus turning moment

In order for a rollover to occur, the conditions explained hereafter must be satisfied.

The first condition would be the rotation of the vehicle around the axis with the outside

wheel as the pivot point. This situation is somewhat similar to one of the worst-case

scenario when a bus collided with a failed guardrail causing the bus to rollover. The

bus will tip on its side given that the lateral sliding moment is larger than the turning

moment:

(Equation 10)

and the kinetic energy of the bus is greater than the potential energy resulted from CG

displacement in height to make it unstable:

(Equation 11)


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In the figure and equations,

m is the total mass of the bus,

is drag factor of the road, is the gravitational constant, is the extended track width, and is the height of CG from pivot point.

Based on the analysis, high-deck buses in Malaysia would most likely to rollover if they

were travelling at 90km/h with an impact angle of 15. The speed of 90 and 120km/h

were considered in the analysis since 90km/h is the speed limit for buses on

expressways while the latter is the maximum speed on the bus tachometer. Impact

angles of 15 and 25 considered were based on the minimum and maximum impact

angles recommended in the NCHRP 350 test. In addition, the range of CG height

between 1.05m to 1.40m is used to represent Malaysian buses.

For another worst-case scenario when a bus collided with a concrete barrier, similar

conditions as described by Matolcsy (2007) still apply. However, this time, the pivot

point is shifted from the outside wheel to top of the barrier (900mm high STEP barrier)

as illustrated in Figure 5-3.

Figure 5-3 FBD ofbus turning moment for collision with rigid barrier

The analysis shows that high-deck buses will most probably survive a collision with a

rigid barrier without rolling over if the vehicle is travelling at 90km/h at a maximum

impact angle of 8. Similarly, at 120km/h the bus will most likely to escape rollover even

at an impact angle of 6 during collision. Additionally, the critical CG height that will not


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result in rollover was found to be 1.56m. From this analysis, it is proven that a rigid

barrier works better than a semi-rigid barrier in preventing high-deck bus rollover.

5.2.2 Rollover at Curve Road

Table 5-3 was taken fromA Guide on Geometric Design of Roads by Malaysian PWD.

It lists the standard minimum radius of a curve to be used for the designated speed

and maximum super elevation rates in Malaysian urban roads. In this table, the

minimum radius of a curve is calculated based on the predetermined designated

speed at the road stretch.

Table 5-3 Minimum Radius of a Curve

Design Speed(km/h)

Minimum Radius (m)e=0.06 e= 0.10

120 710 570100 465 37580 280 23060 150 12550 100 8540 60 5030 35 3020 15 15

Apart from that, the critical speed of a curve can also be determined based on how

sharp the curve is, how much bank is in the roadway, and the coefficient of friction of

the road surface. A vehicle cornering at a speed exceeding this critical speed will begin

to spin around its centre of mass and leave the roadway. Subsequently, the vehicle will

lose control, which can further lead to a rollover. This can happen to anyone regardless

ofa persons driving skill level or years of experience.

A vehicle with higher CG such as a high-deck bus is more vulnerable to rollover, even if

at a speed well below the critical speed of a curve. As a high-deck bus is manoeuvring

a curve, the weight of the vehicle together with its occupant will shift to the front outside

tire due to centrifugal force. Rollover will result if the bus is travelling at high speed

because the CG of the bus shifts as well.


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5.2.3 Design of Vehicle

Current design standards for Malaysia buses require modern engineering techniques

to ensure the integrity of the construction to pursue the new regulation. At the sametime, the Malaysia bus industry stepped forward in bus construction with new the

design of high-deck buses. Most of the designs follow the Australian Design Rules

(ADR). In basic principles, the design of the vehicle shall differ especially in terms of

dimension, weight and interior configuration. Additional factors can also influence the

dynamics of the vehicle.

In order to ensure the safety of high-deck buses during travelling, special safety aspect

should be considered such as a counterweight. The purpose of the counterweight is tostabilize the vehicle when travelling. There are several methods used as

counterweights in bus constructions such as ballast tanks and steel weights. The

ballast tank is commonly placed at the rear side of the vehicle and it is filled up with

water or other liquids. Adding the ballast tank helps the vehicle to lower its CG. It also

prevents the increment of centrifugal force associated with curvy roads. One of the

setbacks when using the ballast tank is when the water is lesser than original settings.

This can cause increment of the CG and high tendency for rollover to occur. The steel

weight is the method that is usually used when constructing the bus frame. Four

pieces of steel, each weighing 1000kg (total 4000kg) is welded on the structure to

lower the CG. Bus manufacturers should also consider in improving the vehicle

structural integrity. The structure must be rollover-proof to prevent injuries and fatalities

of passengers during accidents especially in an event of a rollover. Hence, combining

improvements in rollover strength, seat and seat anchorage strength should be

implemented in all types of buses in Malaysia.


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6. Conclusion

This preliminary literature study was initiated with two main objectives. The first objective of

the study was to carry out analyses of rollover for high-deck bus collisions with crash

barriers through calculations based on formulas derived from a few related literatures. From

the analyses, the location of CG and speed highly affect the stability of a high-deck bus

during rollover event, especially at curved road. The second objective was to assess

existing literatures for any type of traffic safety barriers currently available worldwide for

recommendation on adopting specific crash barrier for high-deck buses to be used in

Malaysia s highways or roads. Based on the study, it is concluded that rigid barrier performs

better than semi-rigid barrier in preventing rollover of high-deck bus during collision with

traffic barriers.

Finally, since the data obtained from the literature research is not extensive enough to carry

out a thorough study regarding the cost-benefit of barrier selection and installation, data

related to statistics of road accidents involving high-deck bus (from RMP) is required with

the RSDs assistance.

7. Recommendations

7.1 Bus Construction

It is time for related regulations to be implemented in Malaysia towards improving local

bus construction. Based on a study carried out on the rollover of heavy commercial

vehicles by the University of Michigan Transport Research Institute (2000), and other

literature reviews, MIROS recommendations for high-deck bus or coach are as follows:a) Vehicle construction and testing

Construction of high-deck buses must consider all the safety requirements and

must comply with the standard regulation. Stability of the vehicle is a crucial part

in the vehicle construction that can influence a vehicle tendency to rollover. Every

aspect shall be considered such as:


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(i) Location of CG

The higher the CG, the more unstable the vehicle will be. The CG

calculation should be compulsory and properly done by a certified

engineer.(ii) Selection of bus chassis

The track width, suspension and tire can influence the vehicle stability in

manoeuvring and cornering. Also, selection of the chassis is crucial to

determine the maximum mass (allowable mass) that a bus can have.

(iii) Dimension and design of the bus frame/body

The dimension of the vehicle shall comply with regulation. Location of the

passenger seat for the high-deck bus must be done properly to ensure

equal weight distribution. Furthermore, the vehicle should be designedaccordingly to suit the road geometric design. The maximum allowable

dimension of vehicle under the current Malaysian legislation is 2.5 meter

wide, 4.57 meter high and 12 meter long.

b) Speed management

High speed can affect the stability and controllability of the high-deck buses

during manoeuvring, cornering and braking. Speeding at corners can impart high

centrifugal force to a vehicle especially to heavier and higher vehicles. This can

cause the driver to lose control of the vehicle and increase the tendency to

rollover. Driving training is a significant method to change the drivers' and fleet

management's attitude, as it is also aimed at improving the efficiency of their

operations and developing driving skills to provide safer services for public

transport customers.

c) Enforcement

MIROS recommends that bus developers should be audited by a government

body to ensure all the regulations are being followed. The inspection should

cover all; from the initial documentation till the finish product. In order to make

sure that the vehicle is safe to be used, it must be tested and certified by a

government body. The test procedure is explained in the Malaysia Road

Transport Rules.


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7.2 Traffic Safety Barrier Consideration

In order to select the use of suitable safety barriers, consideration should be given to the

cost of maintenance as compared to the cost resulted from an accident. The collisionmaintenance should play an important role in the selection of barrier systems since the

majority of maintenance costs are normally due to collision repairs. Therefore, it is not

cost-effective to install safety barrier along the road. Once the installation of barriers is

justified, specific barrier type must be selected considering the barriers performance

capability, deflection characteristics including occupant's risk, site conditions,

compatibility, life cycle costs, maintenance, aesthetic and environmental considerations

as well as field experience, as recommended in the REAMs guidelines. Besides, the

selected barriers must structurally be able to contain and redirect the vehicle (bus) aswell as preventing it from undergoing rollover during collision.

Several studies carried out by international road safety institutions clearly revealed that

traffic safety barriers should only be installed to reduce accident severity at known spots

which have a history of related run-off-road accidents. Hence, based on the findings

through literature reviews and analysis, it is recommended for rigid barriers to be

installed in areas which are known to have a history of bus-rollover accidents. In this

case, concrete barriers such as STEP and vertical wall which can withstand crashenergy of TL-4 and up to TL-6 should be considered for installation especially on

hazardous curves where high-risk of bus-rollover crashes are identified. The selections

are based on the unique energy management characteristics of both barriers (STEP and

concrete vertical wall) in preventing vehicle rollover and lifting.


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References

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