TransportaTion

PHYSICAL LOAD RELATED TO HIGHWAY-DRIVINGAMONG DISABLED PEOPLE
Hiroshi IKEDA

Akihiro MIHOSHI

Interdisciplinary Graduate School of Science and Technology
Kinki University
Osaka, Japan

Faculty of Civil Engineering
Kinki University
Osaka, Japan

Hajimu IKEDA

Yoshio HISARI

Institute for ErgoSciences	Hanshin Expressway Co.,Ltd.
Osaka, Japan
Osaka, Japan(Received November 17, 2006)

Driving environments have been designed basically for travel by physically and mentally unimpaired people. On the other hand,sufficient, special considerations are not given to the vehicles driven by disabled people. In order to examine the ergonomic driving
load put on both disabled and physically unimpaired people while they are on highways, the driving conditions and the muscle-stressof disabled people were evaluated on the approach to curves. Also the influence of acceleration-and-deceleration and centrifugal
force on vehicles were evaluated in straight, split and inter-flows of traffic. The subjects of this study consisted of 5 physically unimpaired people and 10 disabled people who required auxiliaries for their vehicles due to handicaps of their lower limbs or to both upperand lower limbs. The study was conducted on the loop line of the Hanshin Expressway in Osaka, Japan. As a result of measuring theaccelerated velocity of vehicles in motion and electromyograms of drivers of the vehicles, it was found that the driving load of disabled
people is heavier than that of physically unimpaired people. It was also found that certain driving conditions are different for disabled
people to travel at high speed.
Key Words: Disabled people, Vehicle, Highway acceleration, Electromyogram, Steering angle

1. INTRODUCTION
The number of physically disabled people with adriver’s license has been increasing by 4,000 drivers
every year, and it is expected to reach a total of 246,804
in 2004. The National Police Agency1 reported that ofthese people, 206,480 are limited to driving vehicles
specially designed for disabled people, 35,908 people are
permitted to drive provided they use hearing aids, and4,416 people wear a prosthetic limb and/or foot for driving a vehicle. In Japan, the provisional acquisition of adriving license by disabled people was legalized under
Article 88 of the Road Traffic Law in 1960 2. In addition,
the acquisition of a driver’s license by disabled people
with impediments to both upper limbs was legalized in
1982. Recently, the development of barrier-free environments in facilities and on roads in order to support theindependence of elderly and disabled people has comeunder closer scrutiny as a social issue.
In November 2002, the Barrier-free Transportation
Law was implemented. This law involves the promotionof smoother transportation for elderly and disabled people in the public-transportation system. The research

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conducted by Hisari et al.3 into the usage of highways
shows that the development of urban expressway networks has raised the highway use of physically impaired
people as a means to expand their positive contributions
to society. However, driving environments are designedon the premise of travel by physically unimpaired people. In order to assure disabled people’s needs, comfort
and safety when they get involved with society as well as
when they travel, there is demand for: (1) developmentwith an emphasis on vehicles’ ergonomic requirements;and (2) technical support for the safety of disabled people
when they drive at high speed 4.
According to Dols et al.5, the operational procedures and environmental set up for physically impaired
people are unsatisfactory, and almost no ergonomic considerations, which assure their safety and comfort during
driving, are taken into account. Road signs and information provided on highways are also basically for physically unimpaired drivers, thus it can be said that there isno safety and risk management existing for physically
impaired people on highways. If these problems are improved and a stable environment for driving is developed,
not only the improvement of safety and risk management

PHYSICAL LOAD RELATED TO HIGHWAY-DRIVING AMONG DISABLED PEOPLE

but also the reduction of the physical load for drivers will
be realized.
As Kroemer and Grandjean 6 point out, myoelectricactivity has been studied systematically in various fields
as an evaluation metrics for reducing the physical load
which was described earlier. Wikström 7 conducted astudy on the twist of the driver’s body and the effect ofvibration of vehicles while traveling, and Hostens andRamon 8 studied the evaluation of physical load during
the monotonous operation of vehicles. Salvucci and Liu 9,
Imsland et al.10, and Kitahama and Sakai 11 use accelerated velocity and steering angles as evaluation metrics inorder to understand the traveling conditions of vehicles.
The development of a mobile environment is essential for physically impaired people to participate insociety. However, so far, only small numbers of ergonomic studies on their driving conditions on highways
have been conducted. For this paper, experiments wereconducted on the Hanshin Highway Loop Lines and accelerated velocity, electromyogram, and steering angles
were studied in order to understand the driving conditions on highways. Based on the experiments’ results,
this paper explains differences between physically impaired people and unimpaired people and examines thedriving load from the view of ergonomics.

H. IKEDA, A. MIHOSHI, H. IKEDA, Y. HISARI

on highways and traveling conditions of vehicles, bothelectromyogram and accelerated velocity were measured
with a Biopack System MP30 (Monte System Corp.), a
portable 4-channel measurement system. All of themeasured data were recorded onto a personal computer(PowerBook 2400/Apple Computer, Inc.) online. Video
images were also used in order to examine driving performance.
The drivers’ responses were recorded while they
were driving on highways and while they were taking a
10-minute break before they began driving. The average
driving time was 29 minutes 23 seconds (24min 47sec 34min 47sec). Figure 1 is a diagrammatic illustration of
the Hanshin Expressway loop line route no.1, which wasused in this examination. Examiners explained to the subjects of this study about the purpose, method and possible
risks of this experiment. An electrode was attached andthe conditions for measurement were checked. Then theshoulders’ trapezius muscle of the subjects was measured
as an indicator during their rest. Measuring equipment
was set inside the vehicle, and the personal computer was
turned on by using the power source in the vehicle. The
experiment was conducted with the subject’s consent.

2. METHOD
Drivers sense vibrations or the centrifugal force oftraveling vehicles both consciously and unconsciously,
and the driver’s feedback from the information supports
safe driving. The changes of accelerated velocity in traveling and the driver’s muscle tension reflect the driving
conditions. These are important indicators for evaluating
the safety of driving. Acceleration and deceleration of vehicles are shown as accelerated velocity in a front-backdirection, while the information on centrifugal force created by driving on curves or by sudden turning of thesteering wheel is indicated in accelerated velocity in aright-left direction. Using these indicators, the differences of driving conditions between disabled and unimpaired
people were evaluated and examined to study whether
the safety conditions of highways, which were designed
based on travel by unimpaired people, satisfy the requirements for the driving of vehicles by disabled people.
2.1

Procedure for measuring the steering angles, accelerated velocity and electromyogram in order
to examine driving conditions
In order to examine vital reactions when driving

Fig. 1 Diagrammatic illustration of the travel route on
the Hanshin Expressway for the experiment2.1.1 Measuring steering angle
The steering angle is one of the indicators to evaluate driving techniques. Video images of subjects driving
on motorways were shown on the computer screen, andIATSS Research Vol.31 No.1, 2007

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the steering angles were measured from the selectedcurves according to the frame numbers. The upper part ofthe steering wheel on the frontal parallel plane was set as0%, and rotation to the right was set as “minus” and rotation to the left as “plus”. The time required for driving on
a curve was divided into 10 segments, and the starting
point of the curve was set. The associations between thesize of steering angles and the time required on these 11
points were compared.
2.1.2 Measuring accelerated velocity
The conditions of a driving situation were evaluatedby right-left and front-back acceleration indicators. The
gauge for measuring accelerated velocity was set in different places inside the vehicles since the vehicles used
for the measurement were owned by each subject. In
order to obtain the best information about the influenceon the drivers, the acceleration sensors were set on themost stable place near the driver’s seat. The gauge formeasuring accelerated velocity was a tri-axial acceleration gauge SS26L (5g) of the Biopack System (Monte
System Corp.). The sampling speed was 500Hz. The detection zones were DC-500Hz, and the detection range
was 0-5G. Noise which was detected during the drive
over the joints of highways was erased.
2.1.3 Measuring with an electromyogram
The load on the shoulder area of the driver’s trapezius muscle was measured during driving and the measurement was used as an indicator. The trapezius muscle
relates to movements of the head which occur when one’s
shoulder is lifted or when one’s upper limb is fixed. These
kinds of muscle movements indicate people’s muscle
stress, and this is often observed in driving postures andother movements related to driving. The sampling speedof electromyography was set to 2500Hz, and a band-passfilter was used. The myoelectric activity of the rightshoulders’ trapezius muscle was recorded by the bipolarelectrode induction method, and a shield electrode lead
(SS2L) was used. Blue Sensor N-00-S (Medicotest Corp.)
was used for the electrode on the skin surface to induct
vital reactions for the electromyogram.
2.2

Characteristics of the subjects of the experimentTen disabled people and five unimpaired people
participated in this experiment. All of them were volunteers and all of the vehicles used for this experiment were
their own. The average age of the disabled subjects was
46.2 years old (33-66 years old). Five of them obtained adriving license after they became disabled. Their average

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period of driving experience after becoming disabled was
22.8 years (11-43 years). Among the 10 disabled people,
7 subjects had impairment in their lower limbs and 3 ofthem had impairment in both their upper and lower limbs.
All of them belong to the first grade of disability, andeight were classified as first class and two were classified
as second class. They had spinal damage in their cervicalspines and thoracic spine regions. When they were outside, they used manual wheelchairs for mobility. The average age of the unimpaired people was 33.6 years old(23-61 years old), and the average period of driving experience was 14 years (3-44 years).
Four of the vehicles of the disabled people wereToyota’s, 2 were Honda’s, 2 were Nissan’s and 2 were
Mitsubishi’s. The displacement of one vehicle was 2400cc,
8 were 2000cc and 1 was 1500cc. Five vehicles had modified steering in order to assist driving. The accelerator
and brake of 9 vehicles had been remolded, and the alteration was due to impairment in lower limbs. The direction indicators of five vehicles had been remodeled.
Examples of these remodelling are shown in Figure 2.
The left picture shows an example of an assisting aid for
subjects with impairments in the lower limbs, and theright picture is an enlarged view of a part of the accelerator and brake lever.

Fig. 2 Example of assisting aids for subjects with
impairments in lower limbs

2.3

Characteristics of highways chosen for this experiment
In order to understand the traveling conditions of
disabled people on highways, data analysis was conducted on curves, interflow and diverging zones, so that
information was gained from previous interviews andobservation of the driving conditions in which the driving load on the drivers is great. The selected curved zones
are shown in Figure 1 as: Curve-A zone, Curve-B zone,
Curve-C zone and Curve-D zone.
In this paper, each curve zone was divided into 3
sections (Fig. 3). Section 1 is from the starting point of acurve and the nose part of a diverging section. Section 2

PHYSICAL LOAD RELATED TO HIGHWAY-DRIVING AMONG DISABLED PEOPLE

is the area where a safety post is on the wall. Section 3 isthe end of the curve and the nose part of the interflow. In
addition, each zone of straight, split and interflow was
also selected (Fig. 1).

Fig. 3 Definition for the classification of each curvezone

H. IKEDA, A. MIHOSHI, H. IKEDA, Y. HISARI

Curve-A zone and Curve-B zone were multiplecurves and the steering was operated in right-left directions. These curves indicated different changes of steering
angles in comparison with that of the curves describedearlier. In other words, the ranges of the steering by unimpaired and disabled people on Curve-A zone were33.8° and 33.7° respectively, and the difference was 0.1°.
However, the average angles were -2.6° (10.3) for theunimpaired and 3.1° (12.1) for the disabled group, andthe difference was 5.7°. The time changes of steering
angle showed significant differences between these twogroups (t = 4.97, p < 0.001). This result was the difference in the steering angles between the first half and latter half of driving curves. The steering angle decreased
as the vehicle reached the end of the curve with the unimpaired group, however, in comparison, the steering
angle was smaller in the first half and greater in the latter half of the curve for the disabled group. At Curve-B
zone, there were no significant differences between thetwo groups.

3. RESULTS
3.1

Driving load at curve zones based on the performance of steering control of drivers
The average angle for turning a steering wheel by
the disabled subjects between Section 1 and 2 in the curvezone shows a specific result about road structure anddriving techniques on curves. Figure 4 shows the steering
angle when the starting point of a curve is set as 0° andthe end part as 100%. Driving on curves is divided into
two characteristics: single-curve and multiple-curve.
Characteristics of a single-curve can be seen in the driving at the Curve-C zone and the Curve-D zone wheresteering wheels were turned in the same direction fromstart to finish of the curve.
The average steering angle and range at Curve-Dzone were 9.7° (15.5) and 40.4° for the group of unimpaired people, and 16.0° (19.7) and 46.5° for the group of
disabled people. The steering angle on curves showedsignificant differences (t = 3.30, p < 0.008). The angle for
operating a steering wheel displays approximately 6° ofdifference. It was found that in the case of disabled people, the angle of the steering wheel was small just after
they began driving on a curve and it increased as theydrove round the curve.
The average steering angle of Curve-C zone for thegroup of unimpaired people was 12.9° (11.4) and the average range was 30.6°, and for the group of disabled people they were 12.6° (12.3) and 32.9° respectively. There
were no significant differences between the two groups.

Note:		The marks in the figure show the starting points of Sections 2
and 3.

Fig. 4 Comparison of the steering angle between thetwo groups

3.2

Changes of accelerated velocity and driving loadon highways
In order to compare the accelerated velocity between the two groups of unimpaired and disabled people,
the driving time on the selected zones for this analysis
was divided into 100 time-units, and the accelerated velocity of a vehicle driving in right-left and front-back directions was compared. An average time was used forthis data. Figure 5 shows the directions and size of the
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accelerated velocity of the two groups at four curve zones.
The waveform noise of the velocity was smoothed, andthe average velocity was calculated in time units.

Note:		Themarks in the figure show the starting points of Section 2
and 3.

Fig. 5 Comparison of the accelerated velocity between
two groups

As to the accelerated velocity at the four curvezones, the results varied between the two groups. It became clear that some curve zones put more load on the
disabled drivers, and they also experienced more difficulties in comparison with the unimpaired drivers.
Table 1 shows a comparison of average accelerated
velocity and range of the two groups at the curve zones.
As the table shows, the accelerated velocity was greaterin the right-left direction for the disabled group and, except for Curve-B zone, the front-back direction was
greater for the unimpaired group. The accelerated velocity of Curve-A and D zones shown in Figure 5 indicatessignificant differences between the two groups. In comparing the accelerated velocity and the range in the frontback direction between the two groups, the velocity of
the unimpaired group was 1.3 and 1.4 times greater andthe range was 1.4 and 1.2 times greater than those of thedisabled group. The accelerated velocity and the range inthe right-left directions were greater for the disabledgroup. Especially at Curve-A and D zones, the accelerated velocity was 1.4 and 1.5 times greater and the range
was 1.5 and 1.9 times greater than for the unimpaired
group. These results show the possibility that, at thesezones, the disabled people were either conducting an improper reduction of speed or turning the steering wheel
suddenly.
As a result of a t-test for the accelerated velocity ofthe two groups at the four curve zones, significant differences for the right-left direction were found at CurveA zone (t = 2.00, p < 0.05) and Curve-D zone (t=1.97,
p < 0.05). As to the front-back direction, significant differences were found at Curve-A zone (t = 2.86, p<0.05),
Curve-C zone (t = 2.71, p < 0.008) and Curve-D zone(t = 3.02, p < 0.003). At Curve-B zone, the disabled people

Table 1 Comparison of the statistical values of accelerated velocity between the groups of unimpaired anddisabled people
Directions ofacceleration

Right-left

Front-back104

Curve zones

Group of disabled people (N =10)Group of unimpaired people (N = 5)

Average accelerated velocity G
(SD)

Range

Average accelerated velocity G
(SD)

Range

A

0.045 (0.099)

0.345

0.033 (0.059)

0.226

B

0.053 (0.167)

0.661

0.049 (0.162)

0.626

C

0.083 (0.122)

0.492

0.082 (0.126)

0.469

D

0.064 (0.224)

0.810

0.044 (0.131)

0.427

A

0.043 (0.031)

0.126

0.054 (0.036)

0.178

B

0.051 (0.045)

0.201

0.046 (0.063)

0.245

C

0.049 (0.064)

0.212

0.063 (0.054)

0.248

D

0.023 (0.058)

0.200

0.032 (0.065)

0.237

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PHYSICAL LOAD RELATED TO HIGHWAY-DRIVING AMONG DISABLED PEOPLE

kept to their driving state in the same way as the unimpaired people. A similar driving state could be estimatedbetween the two groups at Curve-C zone, though a difference could be found in accelerating and decelerating ofspeed.
Figure 6 shows a comparison of accelerated velocity between the two groups at straight, diverging andinterflow zones. In comparing the accelerated velocity
among the three zones, all of the velocity for the disabled
people was greater except when driving in a front-backdirection at the interflow zone. The result of the t-testshows significant differences for all situations. The average accelerated velocity at the straight zones was
0.123G (0.028) in right-left directions and 0.106G (0.029)
in a front-back direction for the group of disabled people,
and 0.083G (0.019) and 0.083G (0.023) for the unimpaired group. The average accelerated velocity at interflow zones was 0.096G (0.013) in right-left directions
and 0.099G (0.015) in front-back directions for the groupof disabled people, and 0.073G (0.010) and 0.110G(0.027) for the group of unimpaired people. The average
accelerated velocity at diverging zones was 0.114G(0.023) in right-left directions and 0.107G (0.023) infront-back directions for the group of disabled people,
and 0.081G (0.011) and 0.076G (0.019) for the group of

Fig. 6 Comparison of accelerated velocity of the twogroups at straight, diverging and interflow
zones

H. IKEDA, A. MIHOSHI, H. IKEDA, Y. HISARI

unimpaired people.
Next, the driving load was studied by examining
the accelerated velocity at three sections, where safe driving is navigated. This evaluation of accelerated velocity
was conducted by different methods from the indicators
in Figure 5. An absolute figure was calculated after themeasured waveform was equalized, and comparison wasmade by using the figure as an index of the size of theaccelerated velocity. Furthermore, the driving time atcurves was divided into 100 time-units and the average
acceleration during each 1% was calculated. The borderlines of the curve zones for the groups of disabled andunimpaired people were identified, and the average accelerated velocity at each zone was calculated. Figure 7
shows a comparison of accelerated velocity for the twogroups at the three different sections.
Regarding the accelerated velocity in a right-left

Fig. 7 Comparison of accelerated velocity of the twogroupsIATSS Research Vol.31 No.1, 2007

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direction at Sections 1, 2 and 3, the average accelerated
velocity of the disabled people was high in all three sections. In addition, the velocity increased in the order ofSection 1, Section 3 and Section 2. The biggest difference from the result obtained from the group of unimpaired people was at its most significant at Section 2 ofCurve-D zone. This means that it is a typical zone that
disabled people find difficult to deal with. At Section
2, the impact caused by the accelerated velocity in theright-left direction was the strongest. On this section,
drivers feel tension in order to fix their posture, the upper
half of the body leans as a backlash on Section 3 where
the direction of acceleration changes, and then the upper
limb is under strain from the effort to keep the postureand to control the vehicle. Thus, it is possible that more
severe muscle tension is triggered and this will put more
driving load onto the driver than under normal driving
conditions.
Evaluation of drivers’ tension on highways fromthe point of view of muscle activity
In order to examine how the steering angle andacceleration velocity correspond to the activity of the
trapezius muscle of the shoulders, the level of muscle
activity was compared between the groups of disabled
and unimpaired people by applying a method whereby
the curve zones are divided into 100 sections as previously described.
A comparison of the average muscle activity at thefour curve zones shows that myoelectric activity for thegroup of disabled people was higher than that of unimpaired people.
At Curve-A zone, the level of myoelectric activity
was 21.9 (1.89) for the group of disabled people and 18.2
(0.97) for the unimpaired people. It was 23.7 (1.25) and19.5 (1.14) at Curve-B zone. It was 23.7 (1.25) and 19.5
(1.14) at Curve-C zone and 22.4 (2.18) and 20.3 (2.48) at
Curve-D zone. The result of a t-test showed statisticallysignificant differences in all cases. Incidentally, the levelsof muscle activity while the subjects were resting in a sitting position were 9.2 (2.16) for the disabled people and9.7 (2.44) for the unimpaired people.
The best comparison of the level of myoelectric activity is often made by comparing the maximum activityof the trapezius muscle, but the technology for measuring
the activity level of the disabled people is limited. Thus,in this experiment, RMS (Root Mean Square) of theelectric potential of muscle activity was calculated, andthe average-per-time unit was compared. Figure 8 shows
a comparison of the level of muscle activity among three

Note:		Themarks in the figure show the starting points of Section 2
and 3.

Fig. 8 Comparison of the level of muscle activity
among three sections

3.3

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IATSS Research Vol.31 No.1, 2007sections at each curve zone. The comparison of the curvezones and the level of muscle activity are an important
index in order to understand how the disabled people respond to visual signs created according to the criteria of
unimpaired people and what kind of condition they are
driving in.
Figure 9 shows a comparison of the levels of myoelectric muscle activity between the groups of disabled
and unimpaired people while driving on straight, interflow and diverging sections on highways. The resultshows that the level of myoelectric activity for the groupof disabled people was higher than for the group of unimpaired people.
Figure 10 shows a comparison of the levels of muscle activity between the groups of disabled people andFig. 9 Comparison of the level of myoelectric muscle
activity between two groups

PHYSICAL LOAD RELATED TO HIGHWAY-DRIVING AMONG DISABLED PEOPLE

Fig. 10 Comparison of the levels of muscle activity
between two groups

unimpaired people at the four curve zones. Similar to theresult of the comparison of straight, interflow and diverging sections, the level of muscle activity for the group of
disabled people was greater than for the group of unimpaired people in all sections. Furthermore, the level ofmyoelectric activity for the group of unimpaired people
at the curve zones was higher than the myoelectric activity in the straight, diverging and interflow sections, but
this tendency could not be found in the group of disabled
people. A constantly high level of activity was found,which indicates high tension.

4. DISCUSSIONAs Figure 4 shows, the difference of the steering
angle between the groups of disabled and unimpaired
people was significant at Curve-A and D. The angle wassmall when the vehicle enters the curve and it became
larger later. In other words, sudden and rapid control ofsteering caused movement in the upper half of the driver’s body and this put excess load on the driver. This kindof driving load is a burden for drivers and it becomes difficult to maintain posture and driving technique, especially for people with impairment to their lower limbs. In
order to ease this situation, it is necessary to introduce aroad structure and induction methods which disabled
people can find easier to deal with, and the introductionof a warning signal which detects the driving status of adriver is also necessary. The introduction of a seat on
which drivers can easily maintain a suitable posture isalso needed.

H. IKEDA, A. MIHOSHI, H. IKEDA, Y. HISARI

When the temporal response for the turned angle ofa steering wheel was similar in the two groups, it can be
estimated that the situation was also manageable for thegroup of disabled people. If the detailed connection between the driving conditions and road structure is studied, this will be a help to reduce the driving load on
disabled people. However, even if disabled people manage to handle the situation, the driving load for disabled
people cannot be the same as for unimpaired people,
though this should help to maintain the minimum driving
safety. On the contrary, the driving conditions on highways which disabled people can not handle indicates thatthe situation certainly exists in which disabled people
find it difficult to drive at high speed.
As Figure 5 shows, the accelerated velocity at
Curve-A and D zones between the two groups of disabled
and unimpaired people was significantly different in bothright-left and front-back directions. It can be speculated
that the driving load in these situations was heavier forthe group of disabled people and it created a severe driving condition for them.
The accelerated velocity in a front-back direction
shows either acceleration or slowing down of a vehicle,
and this implies that the control of speed by the driver
was different when driving at curved zones for bothgroups. Centrifugal forces on curves influenced the groupof disabled people greatly. The body of a driver swings ina right-left direction when the vehicle enters or exits acurve. If the lower limbs of the driver cannot support theposture of the body, the body has to be supported by theupper limbs, thus creating a heavier driving load on thedriver because the two actions, retaining body postureand driving the vehicle, have to be conducted at the sametime. Especially when the steering wheel is turned backto its previous angle just before the end of a curve, thebody of the vehicle swings a great deal. Disabled people
cannot support their upper body as well as unimpaired
people in order to handle the strong centrifugal force atcurves. Thus, disabled people stretch their upper limbs
and push their shoulders and their backs into the backrestof the driving seat in order to retain the posture of their
upper body. However, at almost the end of a curve, turning the steering back contributes to losing balance forsupporting the upper body.
As Figure 6 shows, the levels of accelerated velocity on straight, diverging and interflow sections were significantly different between the two groups. How thedifference in the accelerated velocity reflects the driving
load for the group of unimpaired people was studied fromthe activity of the trapezius muscle in the shoulders.
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Figure 7 shows, similarly to differences of steering
angles at Curb-A and Curb-D, the level of accelerated
velocity in a front-back direction was high in the group of
unimpaired people and this is an extremely interesting
point. Acceleration in a front-back direction means an increase and decrease of speed. In both groups, greater acceleration of speed was found in Section 1 and the speed
decreased as the vehicle moved to Sections 2 and 3. Thismeans that the driver is traveling in response to road signs
that indicate the driver should slow down, and this isstronger for the group of unimpaired people.
As Figures 8 and Figure 9 show, the level of myoelectric activity was higher in the group of disabled people and this implies that the driving load was constantly
heavy for them. The tension in the trapezius muscle on
the right shoulder relates to the actions of lifting one’s
elbow, fixing the upper body and driving a vehicle. Thismeans that the active mass of the disabled people includes loads which are caused by actions other than driving.
As a result, the muscle tension of disabled people isconstantly high when they are driving on highways, anda driving load is constantly put on the drivers (Fig. 10).
Unlike the case of unimpaired people, when disabled
people are driving, they receive a larger load on theirbody and they are constantly tense in order to deal withthe situation.
The amount of muscle activity at the section ofeach curve became greater in an order corresponding to
Sections 1, 3 and 2 for the group of unimpaired people,
while the level of myoelectric activity became the greatest at Section 3 for the group of disabled people. This
indicates that a driving load in response to the change ofacceleration in a right-left direction was required.

5. CONCLUSION
In this study, it was found that the driving load fordisabled people was heavier than that for unimpaired
people, and it was also discovered that there are somedifficult situations which exist for disabled people when
they try to drive in the same way as unimpaired people.
Driving environments are designed basically for use by
unimpaired people, and building highways with smalland sharp curves is inevitable. However, in this view, it isnecessary to assure safe driving for disabled people andto prevent possible accidents. In order to support safe
driving by disabled people, the following are required:(1) to investigate the driving load for disabled people
based on their driving and traveling situations and to re-

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duce their driving load as much as possible; (2) to predict
danger and to develop traffic-warning systems equippedwith functions for predicting dangerous situations.
As to the reduction of driving load, the installationof driving-aid devices to vehicles built basically for the
movements of unimpaired people and the alternation ofdriving methods are not enough to support driving by
disabled people. With an understanding of this situation,
it is necessary to acknowledge the driving situation fordisabled people scientifically and to understand theirdriving load. When disabled people are driving vehicles,
one of their hands is mainly used for steering the wheel
and another hand is used for controlling acceleration andbraking. They cannot control the steering wheel withboth hands; thus their posture is unstable when they are
driving. Nine out of ten vehicles brought by disabled
people for use in this experiment were also equippedwith a system to control acceleration and braking byhand. In this view, for safe driving by disabled people,
the following are required: (1) driver’s seats which canstabilize the driver’s posture even on curves; (2) development of a human interface system for disabled people;and (3) a support system for safety, such as access to
information on road situations and warning systems
when disabled people drive into the starting point of
curves.
This prediction and providing of road-warning systems is a concept to support safe driving by disabled
people by providing them with information about situations that they can find difficult to detect through the current sensors installed in their vehicles. So far, various
kinds of support systems for unimpaired people havebeen planned, and are now getting ready for putting into
practice.
Induction signs at the starting point of a curve are
one method to provide information and to support safe
driving. If induction systems to reduce the muscle tension of disabled people while driving their vehicles aredeveloped and introduced, unimpaired people will alsofind it comfortable for driving. The road conditions created only for unimpaired people will only increase thedriving load for disabled people.
As a future task, it is important to clarify dangerous
areas from the viewpoint of disabled people. It is also
necessary to evaluate conditions when people drive athigh speeds, and this should happen not only by categorizing the groups of disabled and unimpaired people, butalso by evaluating people individually or by comparing
the conditions with more general roads.

PHYSICAL LOAD RELATED TO HIGHWAY-DRIVING AMONG DISABLED PEOPLE

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ACKNOWLEDGEMENTS
We would like to extend special thanks to Hanshin Toll Road
Service Association and Hanshin Expressway Management Technology Center, for their help in this experiment. We would also liketo extend special thanks to the people who participated in this experiment. Contact to the author: hiroshi.ikeda@union-services.com

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