Chapter

7

Technologies forsafety improvement
Taro Sekine
Associate Professor, Department of Mechanical Engineering, College of Science and Technology,
Nihon University

7.1

Passenger vehicles

This section categorizes by features various technologies for realizing the safety image presented in
Chapter 6 and introduces the technologies with respect to each category of vehicle. We also describe theimplementation timing for the devices shown in Fig. 1, mainly for passenger vehicles.

Areas incorporating safety technologies
Range for reducing the number of deaths due to traffic accidents
Range for reducing the number of traffic accidents
Before accident

Immediately before
Collision prevention

Notification

SupportActive safety
Preventive
SafetyACC
LKA
AFS
Multiview camera

Damage reduction

Pre-collisionsafetyCMBS
E-pretensioner

After accident

Collision

RescueIntervention

Accident avoidance Pre-collision safety
ABS
TRC
ESC

During and immediately after

Automated Collision Notification System

Passive safety
Injury reduction

Damage mitigation

Collision safety body
Seatbelt/child seat
Airbag system
Pop-up hood
Active headrest

Emergency alert system
Energy-sensitive door unlock
systemFigure 1. Areas incorporating safety technologies

7.1.1 Active safety
As of 2013, there are approximately 600,000 automobile accidents in Japan per year, and there is ongoing
research and development and efforts to spread active safety technologies for preventing automobile
accidents through the use of electronics and control technologies.

72｜Theory(1) Visibility enhancement technologies
Today we are seeing the practical use of highluminosity discharge and LED headlights,
which can improve forward visibility at sunset, at nighttime, and during inclement
weather. There has also been increased implementation of adaptive front-lighting systems,
which measure steering angle and vehicle
speed to calculate the forward path of automobiles through turns in order to control thereflective mirrors of the headlight units, orienting them to better illuminate the path oftravel.

Figure 2. Intelligent night vision system enhancing visibility ofpedestrians1)

Indirect visibility is being improved aswell. Installation of multiple cameras onto the car body allows display on monitors of traffic lanes atintersections with poor visibility, displays of the vehicle size superimposed on a rear-view image of the
car when it is in reverse, and displays of the full area around the vehicle. Such fusions of video display
with graphic image processing technologies allows for visibility enhancements of what is happening all
around the vehicle.
Night vision systems to alert drivers of obstacles are also being developed (Fig. 21)). Shining infrared light in the direction of travel during nighttime driving allows use of infrared cameras that can visualize and emphasize pedestrians or road conditions that would otherwise be difficult for the driver to see
with the naked eye.
(2) Driving workload reduction technologies
While traditional cruise control systems maintain a constant speed on highways, adaptive cruise control(ACC) systems monitor conditions in front of the car by using millimeter-wave radar and stereographic
cameras, and automatically adjust travelling speed to maintain a constant distance from other vehicles.
ACC systems can be used not only to maintain speed on high-speed roadways, but also to provide proximity alerts and collision prevention in heavy traffic conditions on general use roads. Low-speed ACC
systems in particular can be used in conjunction with collision mitigation braking systems to avoid or
reduce low-speed collisions, and are looked to as a way of reducing the number of accidents at intersections, which account for the majority of traffic accidents.
Lane departure warning systems that use cameras and lane confirmation technologies are practical.
In addition, intelligent driver assistance systems are being combined with car navigation systems. Thesecan be used, for example, to notify or warn drivers of upcoming intersections at which a full stop is
required.

Chapter 7: Technologies for safety improvement｜73(3) Vehicle dynamic performance technologies
When turning a steering wheel, if tire rotation is locked, then sufficient lateral force cannot be generated
for yaw motion of the vehicle. For that reason almost all cars today have anti-lock braking systems (ABS)as standard equipment. ABS constantly monitors wheel rotation, and in cases where slippery road surfaces cause wheel locking during braking, briefly releases brake pressure to resolve the lock. By thenraising brake pressure in a manner that prevents re-locking, braking can be performed in a manner thatstill permits steering wheel operation.
Electronic stability control systems have been required as a standard feature on all new automobiles
since October 2012. These combine ABS with traction control systems, which prevent tire spinning during starts and acceleration, to provide active unified control of the force generated by each tire and thus
prevent or reduce wobble and sideslip of vehicles. Integrating such systems with electronic power steering and others has also been promoted, which allows for overall improvements to vehicle dynamic performance, realizing better danger and accident avoidance in emergencies.
7.1.2 Passive safety
This section introduces technologies for minimizing damage to humans in the event of an accident.
(1) Collision damage mitigation technologies
The impact that is transmitted to occupants in a collision depends on the vehicle’s momentum, which isthe product of its mass and velocity. In the case of an extremely rigid vehicle body, the impact is immediately transmitted to the occupants, increasing the likelihood of serious injury. Engine compartments
therefore have a “crumple zone” designed to deform and thereby absorb rather than transmit energy,
reducing the amount passed on to occupants. In current methods of frame design, the amount of frame
deformation in the time domain is calculated at the design stage, and design proceeds to ensure that the
impact force delivered to occupants does not exceed a given critical danger value.
In vehicle-on-vehicle collisions, differences in the form of the colliding automobiles can result in
impacts at different frame locations, sometimes significantly lowering the functioning of the crumple
zone. The frames of light motor vehicles and standard class passenger cars are thus now designed toretain some degree of compatibility so that in the event of a collision, the frame of each can function as
designed (Fig. 32)).
Another recent technology for reducing the impact to passengers during a collision is emergency
locking
retractor
seatbelts equippedwith pretensioners
and load limiters.
When a collision isdetected these seatbelts instantly retract
any slack, and thenFigure 3. Schematic diagram of crash-compatible car bodies2)

74｜Theory

the belt is fed out when a certain load is exceeded. Doing so can reduce injury to the chest.
Supplemental restraint system airbags have become standard equipment for both driver and passenger seats. In recent models collisions can be detected approximately 0.015 seconds after they occur.
By varying the airbag inflation rate according to the speed of impact and constantly changing the airbag
volume, passengers with various body types can be better protected. Side impact airbags that inflate in acurtain shape are also being increasingly deployed, and are effective toward reducing head and neckinjuries.
(2) Pedestrian injury mitigation technologies
As a way of reducing injury to pedestrians in the event of a collision, automobile bumpers, fenders, andhoods are now being designed with space beneath them and are being manufactured with easily dented
materials. Hood hinges are also being constructed so that when a strong force is applied to them theyfold so as to absorb energy. Protrusions are being eliminated from car bodies to the extents possible toremove locations where a human body might get caught in a collision; this is one of the reasons why
retractable headlights that pop up only when in use are no longer seen. Yet another safety feature ishoods that pop up at the moment a collision is detected, to produce a larger space beneath them.

7.2

Commercial vehicles

The forms of buses and large trucks are inherently different from those of passenger vehicles, due to theneed to retain space for passengers and cargo. These vehicles are also operated in different ways, and sohave unique safety features according to their characteristics.
Such vehicles are large, and truck beds or loaded cargo can create blind spots from the driver’s seat,particularly to the rear and sides.3) These blind spots are being eliminated through the use of multiple
mirrors as well as rear-facing cameras and sonar equipment that allow for confirmation of the status ofareas of poor visibility. In recent years there have been trials of making the lower portion of passenger
side door panel transparent, to improve side visibility.
Commercial vehicles remain in continuous operation for longer periods than do passenger vehicles, so equipment for monitoring driver attention is in practical use. As an example, certain systems use
cameras to monitor the direction that drivers are facing and the status of their eyes, to ensure they arepaying attention. Another system uses fuzzy logic to analyze the first 15 minutes of driving behavior,and from this can detect declines in driver attention from steering wheel operations and the like. In bothcases, when driver inattention is detected a warning is sounded and displayed. An alarm can also besounded when driver inattention is accompanied by weaving or failure to maintain lanes, and when thishappens multiple times in sequence accidents can be prevented by decreasing the timing before whichcollision damage mitigation braking is applied.4)
With regards to vehicle dynamic performance, heavy-duty vehicles generally weigh more than passenger vehicles, and large loads on trucks can raise their center of gravity. This makes it easier for trucks

Chapter 7: Technologies for safety improvement｜75

to roll over or spin out in turns, leading to accidents. Today, in order to reduce such accidents, electronicstability control systems are being used in heavy-duty vehicles, just like in passenger vehicles.
Approximately 50% of accidents involving commercial trucks are rear-end collisions, and on highways the ratio reaches as high as 72%.5) In an effort to reduce these accidents, implementation of collision mitigation braking systems is beginning to become mandatory for trucks. Trucks also tend to havea large clearance between their body and the road, leading to a submarine phenomenon at the time ofcollision with other categories of vehicles. Vehicle under-run protection devices are therefore currently
mandatory, increasing compatibility with other automobiles as in the case of passenger vehicles.
In the future, we can expect to see more commercial vehicles adopting technologies from the ITS
field, such as spacing maintenance systems (electronic horn system) using road-to-vehicle and vehicleto-vehicle communications devices for comprehending conditions in the vicinity of operation. Also,these are expected to reduce the number of accidents involving other vehicles and to allow the formation of lines of trucks that automatically follow leader trucks, reducing fatigue in long-distance truck
drivers.

7.3

Motorcycles

Motorcycles have two wheels, one in front of the other, and so must maintain balance at all times while
in operation. Control operations are also more direct, such as by the rider directly changing steering
angle or leaning the vehicle while in turns. There are some advanced systems that, for example, adjust
engine output according to the vehicle attitude to prevent rear-tire skidding, but direct intervention
through electronic stability control, such as that used in four-wheeled automobiles, is difficult.
One safety feature that accommodates these differences and is currently in practical use is an ABS
system that uses electronic controls to link the front and rear wheel brakes. Motorcycles have a higher
center of gravity than four-wheeled vehicles due to their shorter wheelbase and higher passenger-to-

braking. Fig. 4 shows the resulting
ideal braking force distribution
curve for a motorcycle. Unlike thecase in four-wheeled vehicles, whena motorcyclist applies sudden braking in excess of 0.5 G, the braking
force on the front wheel must be
increased and that on the rear wheel
decreased. Attempts to apply singleinput braking similar to that in

1000
Ideal brake force distribution
Rear-wheel braking force (N)vehicle mass ratio. This results in ahigher load transfer from the rear
wheel to the front wheel under

800
0.4

600
0.2

400

0.6
0.8

Rider + passenger
Braking decelerationof 1.0 G

200
Rider only
0

0

500

1000
1500
2000
2500
Front-wheel braking force (N)3000

Figure 4. Ideal brake force distribution for motorcycle

3500

76｜Theory

automobiles result in complex apparatuses for rearbrake fluid pressure reduction, which is impractical forpractical application given
the motorcycle’s limited
mounting space. Most motorcycles thus have separate
front and rear brake systems

Power
unit
Valve
unit

Power
unit
ECU

Valve
unit

Front brake

Rear brake
Foot pedal
Hand lever

Figure 5. Diagram of electronically controlled combined ABS6)

that riders themselves must operate independently in attempts to reproduce the ideal braking force distribution curve.
Electronic control of front and rear brakes coordinated through a by-wire can convert rider input
to electronic signals, allowing computers to control both braking and the fine-grained activation of theABS. This electronic control allows elimination of the ABS-dedicated equipment that was previously
mounted on moving parts of the suspension, allowing use of standard parts.6)
Another new technology is dual-clutch transmissions which reduce the shock caused by gearchanges. This allows riders a larger margin of operation, and is expected to reduce the risk of accidents.7)
Regarding passive safety, due to motorcycles’ riding form and much smaller machine size, it is difficult to provide crumple zones like those seen in four-wheeled vehicles. However, through developmentof the ASV, some larger motorcycles now feature airbags. These airbags feature forms, sizes, and inflation methods particular to motorcycles, designed to accommodate the non-restrained seating of arider.8)
In recent years there riding
Advanced Safety Vehicle and Driving Safety Support Systems (ASV/DSSS) tojackets equipped with internallyprevent left-turn accidents
stored airbags have also been [Purpose] To prevent left-turn accidents, information on hard-to-see vehicles is provided some distance backduring left turns at an intersection with traffic signals.
developed. These airbags auto- [Expected benefits] Reduction in the number of left-turn accidents (accident prevention through provision of
information regarding blind spot)
matically inflate when the rider
becomes separated from the
motorcycle due to a collision or
rollover.
Motorcyclists on city streets
frequently travel between lanes

Motorcycle present
Please turn left
carefully

Pay attention to motorcycles
Antenna

Beaconor along road shoulders to avoid
traffic. As ITS becomes morewidespread, road-to-vehicle andvehicle-to-vehicle communications devices like those describedfor automobiles are expected todecrease the number of accidents

Vehicle detection
cameraControl device

Figure 6. Vehicle-infrastructure cooperation under the intelligent transportsystem9)

Chapter 7: Technologies for safety improvement｜77

at intersections or involving cars turning in front of motorcycles, as such devices can alert other vehicles
to their presence (Fig. 69)).

7.4

Other safety technologies

There have also been significant
changes in tire technology. Runflat tires (Fig. 7) have reinforced
sidewalls that allow travel for somedistance following a puncture. This
allows vehicles to be operated

Sidewall-reinforcing rubber
Conventional tireRun-flat tire

Tire shape withnormal inner pressure

Tire shape with
0 kPa pressure

Tire shape with
0 kPa pressure
Sidewall-reinforcing rubber(representative image)without carrying a spare, reducing
Structure of run-flat tire
Mechanism of run-flat tires
with a reinforced sidewallwith a reinforced sidewall
vehicle weight and thus fuelconsumption.
Figure 7. Structure of a run-flat tire10)
Vehicle body component
materials too are changing. While their use remains limited at present, we are starting to see the use ofcarbon fiber-reinforced plastic, in addition to the traditional ultra-tensile steel in consumer vehicles.
This is expected to further reduce vehicle weight, improving running characteristics and decreasing fuelconsumption. As body designs advance, assuming the increased use of such composite materials, freedom of design will allow increased safety over current mainstream body shapes.
Electric and hybrid vehicles are increasingly popular due to their environmentally friendly nature,
but vehicles operating under electric power make much less sound than do those with an engine drive.
This can result in pedestrians being unaware of their presence, increasing their involvement in accidents.
Some such vehicles now issue an electronic sound when operating in electric mode, alerting thosearound them to their presence.
Electric vehicles also containhigh voltage components, so
designs are now taking this inconsideration to prevent accidental electrocution in the eventof accidents.
As society continues to age,
the rise of a new category ofvehicles is becoming apparent:
ultra-compact mobility devices
with very small vehicle footprints
and high maneuverability (Fig.
811)). These vehicles generally

MC-β2,495mm

Light motor vehicle

3,395mm

Minivan

4,690mmFigure 8. Size comparison of ultra-compact mobility devices11)

78｜Theory

Non-Road Vehicles

On-Road Vehicles

For facility and sidewalk use

For on-road use

Rated output(electric vehicles)≤0.6 kWEngine capacity (internal
combustion engine vehicles)≤50 cc>50–≤660 cc>660 cc

Japanese Mopeds

Light motor vehicles

Small andstandard vehicles

As walking aid(no license required)・1 seating capacity
・≤6 km/h
・No safety inspection required ・Maximum loading capacity:
up to 30 kg
・Length: 1,200 mm
Width: 700 mm
・Length: 2,500 mm
Height: 1,090 mm
Width: 1,300 mm
Height: 2,000 mm
・No collision criteria applied・No safety inspection required
・Not for highway use

For use as a walking aid
and support>1 kW

Ultra-compact
mobility devices
・1–2 seating capacity
・Not for highway use

For use in daily living and for the transportation of small goods
Great for a small distance transport

・4 seating capacity
・Maximum loading capacity:
up to 350 kg
・Length: 3,400 mm
Width: 1,480 mm
Height: 2,000 mm
・Collision criteria applied
・Safety inspection required
・Not for highway use

Useful under various circumstances and situations,
including on highways

Figure 9. Ultra-compact mobility devices in comparison with conventional vehicles in Japan12)

allow only one or two occupants, and consume only about a sixth the energy of a standard vehicle (orabout half that of an electric vehicle). They are generally intended for local travel near the home, excursions
at tourist destinations or commercial areas, and small-scale delivery operations, but as they become more
popular, more of these vehicles will likely be mixed in with general traffic, and there will be a need to confirm that they are diﬀerentiated and supplied with sufficient running space (Fig. 912)).
As with motorcycles, these vehicles are very small, making it difficult to design them with crumple
zones. However, as they become more prevalent there will be an increasing need for developing compact, cost-effective collision prevention devices to reduce the number of accidents that they become
involved in.
References
1) Honda Motor Co., Ltd. 2004. “Honda Develops World’s First Intelligent Night Vision System Able to Detect Pedestrians andProvide Driver Cautions: Available on Legend model to be released in Fall 2004.” Honda Worldwide, August 24. Accessed
December 10, 2014. http://world.honda.com/news/2004/4040824_01/video/index.html.
2) Honda Motor Co., Ltd. 2014. “The crash-compatibility body: increasing overall safety for everyone on the road.” Honda
Worldwide. Accessed December 10, 2014. http://world.honda.com/automobile-technology/compatibility/
3) Japan Safe Driving Center. 2007. Ogata kamotsusha no anzen unten [Safe driving of large freight vehicles]. Accessed December 10, 2014. http://www.jsdc.or.jp/search/pdf/all/h18_3.pdf. (in Japanese)4) Mitsubishi Fuso Truck and Bus Corporation. 2008. “Dai 58 kai jidosha gijutsu kai sho de unten chui ryoku monita (MDASIII) ga gijutsu kaihatsu sho o jusho” [Mitsubishi’s Driver’s Attention monitoring system won the Technology Development
Award at the 58th Society of Automotive Engineers of Japan, Inc. award contest]. Accessed December 10, 2014. http://www.
mitsubishi-fuso.com/jp/news/news_content/080424/080424.html. (in Japanese)
5) Japan Trucking Association. 2014. Jigyo yo kamotsu jidosha no kotsu jiko no keiko to jiko jirei [Trends and examples of accidents involving large commercial freight vehicles]. Accessed December 10, 2014. http://www.jta.or.jp/member/
pf_kotsuanzen/jikojirei.pdf. (in Japanese)
6) Honda Motor Co., Ltd. 2014. “Taking super sport riding to a new level-world’s first Electronically Controlled Combined
ABS for super sport bikes.” Honda Worldwide. Accessed December 10, 2014. http://world.honda.com/motorcyclepicturebook/eCBS/.

Chapter 7: Technologies for safety improvement｜79

7) Honda Motor Co., Ltd. 2014. “Enjoy the performance of a manual transmission with the convenience of an automatic.
Honda introduces the world’s first dual-clutch transmission for use in a motorcycle.” Honda Worldwide. Accessed December
10, 2014. http://world.honda.com/motorcycle-picturebook/DCT/.
8) Honda Motor Co., Ltd. 2014. “The world’s first production motorcycle airbag system, designed to help lessen the severity of
injuries to the rider in a frontal collision.” Honda Worldwide. Accessed December 10, 2014. http://world.honda.com/
motorcycle-picturebook/Airbag/.
9) Honda Motor Co., Ltd. 2008. “Honda Begins Testing of Advanced Safety Vehicles and Driving Safety Support Systems on
Public Roadways: Honda Cooperating on Development of Driving Safety Support Systems Using Inter-Vehicle and Road-toVehicle Communications to Help Reduce Traffic Accidents.” Honda Worldwide, March 24. Accessed December 10, 2014.
http://world.honda.com/news/2008/4080324Advanced-Safety-Vehicles/.
10) Bridgestone Corporation. 2014. “Key components of Run-Flat Technology tires.” RFT: BRIDGSTONE Run-Flat Technology.
Accessed December 10, 2014. http://www.bridgestone.com/sc/runflat-system/technology/index.html.
11) Honda Motor Co., Ltd. 2013. “Honda Unveils MC-β, New Micro-sized EV: Field tests will begin in Kumamoto, Saitama andMiyakojima.” Honda Worldwide, November 19. Accessed December 10, 2014. http://world.honda.com/news/2013/
4131119MC-Micro-sized-EV/index.html.
12) Ministry of Land, Infrastructure, Transport and Tourism. 2013. “Cho kogata mobiritei no donyu sokushin” [Promotion ofultra-compact mobility vehicles]. Accessed December 10, 2014. http://www.mlit.go.jp/common/000986236.pdf. (inJapanese)
Recommended Reading
1) Society of Automotive Engineers of Japan, Inc., ed. 2009. Jidosha no hyakka jiten [Encyclopedia of automobiles]. Maruzen
Co., Ltd. (in Japanese)2) Ministry of Land, Infrastructure, Transport and Tourism. 2008. “Senshin anzen jidosha ni kansuru kenkyu seika hokokusho:
ASV (Advanced Safety Vehicle) no kenkyu seika to kongo no gijutsu houshin” [Report on research results regarding
Advanced Safety Vehicle: Results of research on ASV and future technological guidelines]. Accessed December 10, 2014.
http://www.mlit.go.jp/jidosha/anzen/01asv/resourse/data/asv1report.pdf. (in Japanese)3) Ministry of Land, Infrastructure, Transport and Tourism. 2001. “Senshin anzen jidosha (ASV) suishin keikaku (dai 2 ki) ni
kansuru hokokusho” [Report on promotion plan for advanced safety vehicles (2nd stage)]. Accessed December 10, 2014.
http://www.mlit.go.jp/jidosha/anzen/01asv/resourse/data/asv2report.pdf. (in Japanese)4) Ministry of Land, Infrastructure, Transport and Tourism. 2006. “Senshin anzen jidosha (ASV) suishin keikaku hokokusho:
dai 3 ki ASV keikaku ni okeru katsudo seika ni tsuite” [Report on the promotion plan for advanced safety vehicles: results of
ASV promotion plan (3rd stage)]. Accessed December 10, 2014. http://www.mlit.go.jp/jidosha/anzen/01asv/resourse/data/
asv3seikahoukokusyocorrection.pdf. (in Japanese)5) Ministry of Land, Infrastructure, Transport and Tourism. 2011. “Senshin anzen jidosha (ASV) suishin keikaku hokokusho:
dai 4 ki ASV keikaku ni okeru katsudo seika ni tsuite” [Report on the promotion plan for advanced safety vehicles: results of
ASV promotion plan (4th stage)]. Accessed December 10, 2014. http://www.mlit.go.jp/jidosha/anzen/01asv/resourse/data/
asv4pamphlet_seika.pdf. (in Japanese)
Practical application projects for reference
A study on the role and limitations of motorcycles as a means of urban transport in Southeast Asia: 156–159