Considering the above, what is presently most important is to first focus our attention on cases in which the causes are clearly understood, where the information and control technologies provided will lead to a reduction in the number of traffic accidents. After implementing practical applications and achieving successful results, I think it is important to patiently work on the more difficult cases and resolve them in the coming years.
When analyzing accident fatalities by situation and age, a large number of accidents involve young drivers or elderly pedestrians. Cases where the cause is clearly understood include those such as right-hand turn accidents, head-on collisions and left-turn accidents involving motorcycles at intersections. It is desirable to work on these types of cases because the causes are clearly understood, and it is possible to obtain successful results through experience.
I will now introduce some of the work conducted to obtain successful results. The first example is a study about the Awaza Curve on the Hanshin Expressway, which began more than 10 years ago. This curve is known for poor visibility, where the layout of the road does not allow the driver visibility ahead of the curve, and it is difficult for drivers of vehicles entering the curve to notice when traffic is being held up by an accident. Given these facts, efforts were made to prevent secondary accidents by using monitoring cameras and image-processing technology to detect stopped vehicles and provide the information to the drivers of approaching vehicles via information boards.
The second example is an experiment conducted at Sangubashi, on the Metropolitan Expressway. In Japan, the probability of an accident occurring on urban expressways where the radius of the curve is less than 200 meters (R200) is 2.6 times more than all other places. The radius of the Sangubashi Curve is 80 meters, and more accidents occur at this curve than anywhere else on the Metropolitan Expressway. On the other hand, causes for the accident such as delay in detection, error in judgment and error in control account for more than 75% of the total number of accidents. Given these facts, it was deemed that an effective way to prevent accidents would be to provide information through vehicle onboard sensors and road-to-vehicle communications.
However, in curves with a small radius like the Sangubashi Curve, it is impossible to detect obstructions using sensors mounted in vehicles. For this reason, information was provided using cooperative driving, which is achieved through communications between roadside facilities and vehicles.
General automobile owners that use onboard VICSs were recruited as monitors and experiments were carried out; more than 200 people were employed as monitors. The monitor vehicles were equipped with a space-sensing infrared sensor that detects the roadside, and information boards and a radio-wave beacon were used to collect information on stopped and low-speed vehicles. The results of the experiment showed the provision of information dramatically reduced the number of accidents during the experimental period. However, it cannot be said that this remarkable result was solely due to the experimental measures because road surface maintenance (i.e., drainage grooves were being cut) was being done to the expressway during the experimental period.
My experiments show that it is possible to attain objectives through experience, but the causes of many accidents are yet to be defined. One of the efforts made to clarify them was an experiment conducted by my laboratory, where we used video surveillance in the Akasaka Tunnel to detect the cause of accidents. In the experiment, over 100 accidents were detected in a three-year period. Analysis of the information showed that most of the causes for accidents in the Akasaka Tunnel were related to the vehicle-spacing compression wave that is generated as the result of applying brakes at the time of poor vision.
One of the methods considered to be effective for reducing the number of accidents at intersections is reducing the dilemma zone. The dilemma zone is the time duration after the streetlight changes from green to yellow. In that zone, a vehicle is unable to stop without suddenly applying the brakes, while at the same time, it is not possible to travel at the same speed and make it through the intersection before the light turns red, so acceleration is required if it is decided to pass through the intersection. In order to prevent this decision-making dilemma, it is thought that it would be effective to add controls that could, for example, detect the vehicle location and speed information once it enters the dilemma zone, compare the data to the status of the light and delay the time the light changes from green to yellow.
Lastly, regarding ensuring the safety of pedestrians, they do not have onboard equipment and an individual can act in a variety ways. In view of the many unknowns, this area is still under investigation. The reduction of accidents by controlling traffic lights and stopping all vehicles when pedestrians cross the road is effective. However, this could lead to traffic congestion or other problems. Many issues remain to be studied.