|
 |
 |
Hiroyuki Mizutani General Manager, Planning and Evaluation Department AHSRA |
1. Overview of Proving Tests Implementation
I will present a report that combines an overview of the implementation of proving tests with a description of the content of AHS tests and the evaluation results. The proving tests conducted in 2002 were configured broadly to, first, evaluate cooperative vehicle-highway with the ASV, second, test infrastructure-based systems, including information boards and so on, and third, work with road administrators to test application for road management.
Tests were implemented in the three fields of the test course,
actual roads, and a driving simulator. The testing was allocated and coordinated
according to the characteristics of these fields in order to conduct overall
verification and evaluation. (Figure 1)
 |
|
Figure 1 |
Testing on actual roads was conducted at the selected locations
shown in Figure 2. The test sites for cooperative vehicle-highway were selected
for their social significance and for their potential as locations where services
would have a full impact.
 |
|
Figure 2 |
2. AHS Testing
AHS evaluation from the perspective of road infrastructure
was carried out by the following criteria: Whether provision of services (information
about the road) would be effective, whether services would be used, whether
infrastructure design values were valid, whether the safety and reliability
of infrastructure could be assured, the extent to which it would be effectively
utilized for road management, and so on. (Figure 3)
 |
|
Figure 3 |
These evaluations were made by testing stand-alone AHS systems and testing system performance, to include those portions that function jointly with ASV. The feasibility of AHS services as vehicle services was evaluated by ASV in joint proving tests. Testing of AHS services for feasibility as vehicle services extended to the questions of whether drivers would accept the services without any problem, whether infrastructure design values were valid in terms of services for vehicles, whether systems could be created to provide solid information to drivers in their vehicles, and so on.
Here I would like to describe the AHS testing from the perspective of road infrastructure.
(1) Advanced Cruise-Assist Highway Systems for Road Sections of Uninterrupted Flow Field
For road sections of uninterrupted flow field, three systems
were created for services to provide information on standing and slow vehicles
ahead, to prevent overshooting on curves, and to provide road surface condition
information. We succeeded in creating road systems aimed to enable safe driving
by providing advance information on conditions ahead that drivers and vehicles
either cannot perceive directly or cannot perceive easily. (Figure 4)
 |
|
Figure 4 |
The common features of these three systems for road sections
of uninterrupted flow field are shown in Figure 5.
 |
|
Figure 5 |
The uniform architecture was devised by making the functions into modular components and setting a standard interface to fit between them. This approach is distinctive in making it possible not only to provide combined services, but also to simplify construction, improvement, and maintenance management. In the following I will describe the individual systems.
[1] Support System for Provision of Information on Standing and Slow Vehicles Ahead
An actual obstacle was placed on a test course and the driving
behavior of some 30 test subjects was measured as they drove through with and
without services. (Figure 6)
 |
|
Figure 6 |
Sudden actions on discovery of the obstacle, such as braking sharply, diminished when services were provided. The driving speed when the obstacle first came into view was also lower when services were provided. We consider this to confirm that the provision of information tends to change behavior to the safe side.
Surveys were also conducted to determine the reactions of
test subjects when they experienced those services for themselves on actual
roads. Tests on National Highway No. 25 (the Maitani District of the Meihan
Highway) showed a high frequency of slow and standing vehicles. In 200 tests,
the 19 subjects were able to receive information provided on slow vehicles.
Those subjects responded affirmatively when asked both if this service seemed
likely to be of use in avoiding accidents and driving safely, and whether they
would like their parents or elderly people to use the service. (Figure 7)
 |
|
Figure 7 |
On the other hand, we also evaluated the effects of information
provision to non-AHS vehicles by the medium of information boards (Figure 8).
 |
|
Figure 8 |
Measurement points were established before and after two information boards on the Maitani District road. The speed of vehicles before seeing the information boards and the speed of the same vehicles after seeing the boards and beginning to enter a curve were measured and compared. This confirmed that the fall in these speeds becomes greater when information is present, and the results were statistically significant.
Test subjects were also asked the extent of their expectations
for on-board services. The majority of responses indicate the expectation that
on-board services would be much more useful than message signs. One of the features
of road sensors used by AHS to detect obstacles, standing vehicles, and slow
vehicles is that they detect all the incidents and conditions in the service
area. The graph in Figure 9 shows tracking traces of vehicles with the distance
of the curve in the vertical axis and time in the horizontal axis. This can
track all incidents and conditions in the entire curve area. Let us say, for
example, that two slow vehicles appear on the curve at the same time. The system
can utilize this information in various ways, for instance by informing drivers
only of the closer vehicle on the upstream side, or by informing them of all
dangerous incidents and conditions.
 |
|
Figure 9 |
Performance evaluation of the sensors also applies the measure of safety. Safety is the index form of the percentage of failures to detect, that is, the ratio of times when sensors were unable to find standing or slow vehicles that were actually present.
Infrared type road sensors were tested at the Kamiyashiro
Junction and Nagoya Nishi Junction of the Higashimeihan Expressway. Human beings
viewed several hundred hours of video to identify incidents. Their findings
were then compared with the sensor findings to see if the same incidents had
definitely been detected. The sensors did detect all incidents within the scope
of this test. The number of false reports was also quantified, and we found
that the sensors mistakenly reported standing vehicles at the rate of 0.5 or
fewer incidents per day. (Figure 10)
 |
|
Figure 10 |
One concern in communications is shadowing, in which radio waves do not reach a vehicle because of another vehicle overlapping it. Another is reflection from buildings and structures along the road (multipath), which can cause communication quality to deteriorate or even make communication impossible. There is also concern over the influence of radio wave leakage to adjoining lanes, to oncoming vehicles, or to roads underneath an elevated road structure.
During field operation tests, the probability of shadowing occurrence was determined by attaching a camera at the actual antenna location in order to estimate whether radio waves could travel directly to the target. The camera was used to quantify the number of vehicles that could be in shadow, and it was confirmed that shadowing would only occur at a rate equal to or lower than the target value.
For the multipath problem, a multipath environment was created
on the test course. Vehicles were driven through it 500 times and any deterioration
in quality was measured. Here, too, the results showed that target values were
met. Radio wave leakage to adjacent lanes was measured, and within the scope
of on-board receiving unit used in the current testing, we confirmed that no
mistaken service-in occurred in oncoming vehicles or below an elevated road
structure. We consider that overall communications safety cleared the provisional
target value of 99.1 for safety. (Figure 11)
 |
|
Figure 11 |
Since 100% safety and reliability cannot be achieved at a reasonable cost, it is necessary to consider residual risks.
Therefore we created a three-state display that displays
a message to encourage cautious driving under conditions of detection failure
by sensors, when information is not communicated due to shadowing, and so on.
A blank display also allows the driver to know when shadowing or equipment failure
has occurred. In order to determine whether this display is actually useful,
we conducted tests with the AHS simulator loaded on the driving simulator at
the Japan Automobile Research Institute (JARI). (Figures 12 and 13)
 |
|
Figure 12 |
 |
|
Figure 13 |
Provision of information to promote caution produces some
degree of speed-limiting effect. Furthermore, we also confirmed that the effect
of a blank display is at least no worse than providing no service. This confirmed
the possibility that these measures could serve as a failsafe function. (Figure
14)
 |
|
Figure 14 |
[2] Support System for Prevention of Overshooting on Curve
We confirmed on the test course whether the presence and absence
of service from the curve overshooting system would change test subject behavior
to the safe side. When subjects were informed in advance of entering a curve
that they should reduce speed, and when not service at all was provided, there
was a confirmed tendency to enter the curve at a speed on the safe side. (Figure
15)
 |
|
Figure 15 |
The curve overshooting service was provided at five locations
on actual roads. After going through curves, test subjects were asked whether
they thought the service would be useful, and whether they would like their
parents or elderly people to use the service. The responses are excerpted, and
generally show a very positive assessment of the service. A larger number of
affirmative response was received on the four expressways, in particular. (Figure
16)
 |
|
Figure 16 |
[3] Support System for Road Surface Condition Information
Tests of the road surface system were conducted in the Maitani
District on the Meihan Expressway and at the Miyako Tunnels on National Highway
No. 45. The tests were largely in the form of questionnaires. (Figure 17)
 |
|
Figure 17 |
As a result, we found that the number of responses indicating that information provided in the form of "Watch out for slipping" in the case of wet roads would be useful in avoiding accident and driving safely was not as high as anticipated (80% or more).
The tests at the Miyako Tunnels provided information in advance about road surface conditions at tunnel exits using message signs inside the tunnels. Although no freezing had actually occurred, when the test subjects were asked whether they would be glad to have information about frozen conditions provided, their responses indicate that they would like such a service. We consider, therefore, that it is effective to use the road surface system to provide information when road surface conditions are different on the road ahead.
Vehicles that passed through the Miyako Tunnels were given
information on road surface conditions while still inside the tunnel. The road
surface sensor shows dry conditions in red on the screen, wet in green, snow
cover in white, and so on, and one distinctive feature of the AHS system is
that it allows us to grasp road surface conditions over a surface area. (Figure
18)
 |
|
Figure 18 |
Evaluation was performed to determine whether safety would
surpass the provisional target value of 96%. The result was 95.5%. Here the
vertical axis shows road surface conditions that actually occurred (as determined
visually by specialists), while the horizontal axis shows the road surface condition
detected by the sensors. The results are represented as a matrix. The provisional
target value for the individual sensing accuracy rate was set to exceed 90%,
and we consider this target to have been cleared with the exception of water
film. (Figure 19)
 |
|
Figure 19 |
If we suppose, for example, that the sensor reports a wet surface when actually there is snow cover. It is conceivable that drivers might be over-confident, and assuming that they are safe, they could actually be endangered. Therefore, we consider that having fewer triangular portions at the bottom left indicates a numerical value representing safety.
On the other hand, optical fiber type road surface sensor was verified using tests in the Maitani District. The result was 92.6% safety, which falls slightly short of 96%.
[4] System Safety and Reliability
The provisional target value for the system was set at 95%. Allocating this
between the sensor system and communications system, the target values for occurrence
of danger are 4%, and 0.9% or less. In verification on actual roads, we generally
achieved 95% or better. The availability rate was set at 95% or better. This
is the time when the system is able to provide services, excluding those times
when sensors give up and are unable to provide service, when communications
are unavailable due to shadowing, and so on. The system is known to clear this
requirement, so long as system installation standards are satisfied. (Figure
20)
 |
|
Figure 20 |
Verification of system safety yielded the following findings
(Figure 21)
 |
|
Figure 21 |
First, it is possible to build a support system for provision of information on standing and slow vehicles ahead that satisfied the provisional target values for safety and reliabilityusing infrared camera type road sensor. This was verified, although the test period was limited to one month.
Second, visible image camera type road sensor yielded 95% during the day and 86% at night. We found that it is necessary to make certain of installation conditions regarding illumination at night.
Third, visible image type road surface sensor largely satisfies the safety requirement.
Fourth, optical fiber type road surface sensor requires further work on tuning for use on roads surfaced with draining material and roads where snow melting agents are scattered.
Fifth, we found that the communications system can clear the provisional target value at testing locations where large commercial vehicles make up a large percentage of traffic if installation observes the standard for roadside antenna placement at a height of 8 m above the white line.
[5] Subjects (Figure 22)
First, sensor systems have not yet been verified under the
changing characteristics of all four seasons. Therefore, measurements will be
made in the current fiscal year to obtain year-round data, and evaluation will
continue. Proving tests at Sangubashi are also scheduled to include verification
in an environment experiencing congestion. Second, when considering Cooperative
Vehicle-Highway Systems as AHS, promotion of widespread installation of the
equipment in vehicles becomes an issue. For the time being, therefore, we intend
to study the operation of infrastructure-based systems using message signs.
 |
|
Figure 22 |
2. Advanced Cruise-Assist Highway Systems for Use in Intersections
Proving tests were conducted of AHS for use in intersections,
and the results clarified the subjects involved. We discovered that there are
several subjects with layout of infrastructure for support for prevention of
right turn collisions and support for prevention of collisions with pedestrians
crossing streets. (Figure 23)
 |
|
Figure 23 |
The testing served to organize classic traffic patterns in
intersections as derived from accident analysis and other means. Using vehicles
following those patterns, we isolated the subjects of system function and performance
(Figure 24).
 |
|
Figure 24 |
The tests were implemented to determine whether sensors could
accurately capture two-wheeled vehicles squeezing through traffic at locations
where this occurs, and whether drivers could be informed of this using communications.
(Figure 25)
 |
|
Figure 25 |
The results from tests for detection of oncoming vehicles
showed that it is possible to detect such vehicles when dealing with less complex
patterns with a single vehicle or a single vehicle squeezing through. When multiple
oncoming vehicles create a more complex situation, however, it is difficult
to detect them all accurately (Figure 26). Therefore, we find that accurate
detection is difficult when multiple complex situations occur.
 |
|
Figure 26 |
In the area of communications performance, there are limits
on continuous transmission to vehicles. Sudden interruptions in communications
occurred in particular while waiting to make a right turn at an intersection,
probably because of multiple reflections. The influence of vehicle front windows,
and sometimes the influence of multiple reflections inside the cabin, sometimes
result in sudden drops in communication quality. However, this is something
that cannot be resolved by measures on the road side alone. (Figure 27)
 |
|
Figure 27 |
There are also concerns about communications shadowing caused by the vehicle ahead, and there is also a problem with deterioration of reception characteristics due to swinging of the vehicle noses when large commercial vehicles make right or left turns. Consequently, we find that there are also limits to propagation performance in communication.
There are limits to the support that can be provided by road
infrastructure alone under the present system configuration. However, intersection
accidents make up half or more of all accidents, so we consider countermeasures
to be essential. We find it necessary, therefore, to review the requirements
and the road-vehicle allocation of functions, and to reexamine infrastructure-side
functions, and so on. (Figure 28)
 |
|
Figure 28 |
3. Basic Study of Technology for Future Application
Now I would like to introduce two categories of basic tests that we conducted as related tests.
(1) Merge Support Service
Congestion of converging vehicles can occur in merge sections
of expressways, making support for flow regularization an issue. AHS selected
one method and conducted tests of its feasibility. This is known as the main
roadway guidelight method. The system gauges merging vehicles that cannot be
seen from vehicles in the main roadway and activates guidelights that can be
seen from the main roadway to notify those vehicles to expect merging vehicles.
This service works on the expectation that those vehicles will slow down, open
up their headway, and take other such measures. (Figure 29)
 |
|
Figure 29 |
A temporary merge section was created on the test course
and the service was tested. (Figure 30)
 |
|
Figure 30 |
The test results showed that provision of this service yielded
a reduction of the danger index, a reduction also in the magnitude of deceleration,
and a reduction in cases of headway that constitute dangerously close following.
The current tests did not make use of sensor systems. However, the guidelight
method can be expected to have a speed limiting effect, and it has possibilities
for use in regularizing traffic flow. We hope to make use of this method in
our coming research. (Figure 31)
 |
|
Figure 31 |
(2) Application use of DSRC
Application use of DSRC makes use of on-board ETC communications
modules in vehicles to perform simple transmission of information to vehicles
over antennas about 3 m in height arranged along the roadside. As the system
is portable, we envision using it as a kind of electronic signboard. (Figure
32)
 |
|
Figure 32 |
In terms of performance, we learned that this system could transmit to vehicles over an area of approximately 15 m X 7 m. The data volume indicates that the system is capable of transmitting VICS level 2 information (simple diagrams). There is the possibility, for example, that with portable antennas placed in appropriate locations, the system could convey the information that a construction area with traffic restrictions is ahead, or information about curves and intersections. We intend to examine the practical applications in our future research.
4. Subjects for the Future (Figure 33)
(1) Short-Term Technical Subjects
During the present fiscal year, we will implement verification in environments subject to congestion, verification of the year-round changes in sensor characteristics, and continued verification of the effective application of AHS systems for road management.
(2) Subjects for Practical Application
We consider it necessary to build up mechanisms for standardization and unification in order to assure quality, even though we do not necessarily expect to implement them in the AHSRA.
(3) Medium and Long-Term Technical Subjects
We intend to carry out study of new requirements for intersection systems, to include a reevaluation of system functions and of the allocation of functions between road and vehicles.
 |
|
Figure 33 |
 |
|