Research outline

Development of Wire Rope Guardrail Systems with Shock-absorbing function to reduce Fatal Traffic Accidents

Wire rope guardrail systems


Wire rope guardrail systems

researched and developed by CERI

Impact testing

(car and heavy goods vehicle)

Roads in suburban areas usually have one lane each way without median divider. On these roads, vehicles travel at relatively high speeds, resulting in a high incidence of head-on collisions and other fatal accidents. To reduce the occurrence of such accidents, the Civil Engineering Research Institute for Cold Region (CERI) is currently researching and developing wire rope guardrail systems with shock-absorbing function as a new type of median divider.

Unlike the structures of conventional barriers, the wire rope type consists of thin, bendable posts and several cables. Upon vehicle impact, the posts give way and the cables flex and prevent the vehicle from exiting the lane. As these barriers can absorb such impact, they are expected to contribute to a significant reduction in the incidence of fatal and other serious accidents.

Wire rope guardrail systems are also advantageous in terms of construction costs and maintenance/management. For example, the installation space required is less than that for conventional dividers, which leads to cost reductions. In addition, the cables and posts are designed to allow manual attachment and detachment. In an emergency situation, such as the occurrence of vehicle disablement or an accident, a barrier can be partially dismantled to allow vehicles to use the opposite lane for traffic control.

Thanks to these characteristics, the effectiveness of wire rope guardrail systems in reducing fatal accidents has been reported in other countries where they have already been installed. However, for installation in Japan, such barriers must meet the country’s standards, the most critical of which is that entry into the oncoming lane must be prevented to a specific extent. Wire rope guardrail systems are designed to flex and absorb shock, but overly flexible cables may fail to meet the required standard. Thus, the specifications of wire rope guardrail systems must achieve a balance between these conflicting requirements. Against this background, CERI began joint research with the Steel Barrier Association (a group of manufacturers related to the field) in which barrier structures were first examined through simulation, and impact tests were performed using actual cars and heavy vehicles. As a result, a basic structure that meets the required standards was established.

The joint research continuously addresses problems related to winter maintenance/management and other issues. It is expected that wire rope guardrail systems will be actively installed on suburban roads with one lane in each direction in the near future as median dividers that satisfy the requirements of both safety and cost.

(Contact: Traffic Engineering Research Team, CERI)

Recent Changes in Drift Ice and Wave Heights in the Sea of Okhotsk

Drift ice

Drift ice distribution as of Feb. 4th, 2011
(Source: Ice Information Center website)

Long-term changes in
drift ice area and wave height

Recent changes in the probability of
drift ice formation and wave heights

Drift ice in the Sea of Okhotsk provides rich fishing grounds and acts as a tourism resource, bringing a variety of benefits to the local economy. In terms of coastal disaster prevention, it also has the effect of reducing the height of waves washing against coasts. The first figure here shows drift ice distribution as of Feb. 4th, 2011, and indicates that it reached coastal areas extensively along the Sea of Okhotsk. At that time in Hokkaido, high waves caused by a winter pressure pattern were observed in areas along the Sea of Japan and the Pacific Ocean. Meanwhile, coastal waters in the Sea of Okhotsk were relatively calm compared with other waters. In this way, drift ice can be considered effective in helping to prevent wave-related disasters. However, its total area in the Sea of Okhotsk has shown a decreasing trend lately.

The second figure shows changes in the drift ice area in the Sea of Okhotsk over the 30-year period from 1979 to 2008. It can be seen that the area fluctuates significantly from year to year, but shows a long-term gradual trend of decrease. In contrast, the wave height during winter has increased yearly, and tends to be high in winters when there is less drift ice.

The third figure shows recent changes in the probability of drift ice formation and wave heights in waters surrounding Hokkaido. Recently, the probability in the Sea of Okhotsk has decreased, with a reduction of 10% or more seen in some waters. Wave height, on the other hand, has increased in various parts of the Sea of Okhotsk and around the Kuril Islands in addition to those around Hokkaido.

Accordingly, there are fears that the safety of breakwaters, revetments and other coastal facilities may be significantly compromised when this reduction in the presence of drift ice combines with other future influences, such as increased wind velocity and higher sea levels triggered by global warming.

Against this background, CERI’s Port and Coast Research Team began a research project in April 2011 to estimate the extent of future changes in wave characteristics in the Sea of Okhotsk. In this study, numerical computation is performed to estimate future wave heights. A technique for calculating the effects of drift ice on the development and attenuation of waves will also be examined, and future changes in the safety of coastal facilities against high waves will be estimated.

(Contact: Port and Coast Research Team, CERI)

“Medical Checkups” for Deposited Snow
-Snow Cover Profile Observation-

Photo 1: Excavating the snow cover
on the slope and shaping the snow wall

Photo 2: Sampling snow in a predetermined volume
with a sampler for density measurement
and measuring snow with a scale

Photo 3: Snow crystals as observed
by the loupe (3 mm per side of the grid)

Fig. 1: Observation results showing hardness
changing with depth
( the colored areas;
it becomes harder as you go left)

Periodic medical checkups are one of the most basic means of physical management of the human body. When the same process is used to gain an understanding of the conditions of deposited snow, it is called “snow cover profile observation.” From the moment snow touches the ground, temperature and sunshine causes its properties to begin to change. It is therefore clear that an accurate understanding of the properties of snow requires periodic observation. The Snow Avalanche and Landslide Research Center conducts snow cover profile observation on slopes and flatlands once every 10 to 20 days, working jointly with the researchers of the Snow and Snow Ice Research Team (Sapporo), the Tokamachi Experiment Station of the Forestry and Forest Products Research Institute (Tokamachi City, Niigata Prefecture), and the Toyama National College of Technology.

Profile Observation Procedure

(1) Positioning

While locations where snow cover differs by locale, such as snow drifts, should be avoided, spots surrounded by a relatively wide area are preferable, as it is necessary to observe the snow cover at positions that are slightly different from the first spot. When making observations on the slope, special attention should be paid to the danger of snowslides. In the event of an emergency, it is necessary to have an evacuation route prepared in advance.

(2) Excavation

Just dig and dig and dig (Photo 1).

In the pit excavated in the compound of the Center, the greatest depth of excavation is about 3 m. An observation pit measuring 2 m wide, 2 m long, and 3 m deep is necessary to ensure space for observers. Assuming that the density of snow cover is 400 kg/m3, it means that snow in the volume of about 5 tons has to be dug out by human power.

(3) Observation

Observation is conducted for the following items using visual checks, haptic checks, and measuring equipment (Photos 2 and 3):

Observation items Means
Laminar structure  Visual
Snow quality  Loupe and visual
Snow temperature  Thermistor thermometer
Grain size  Loupe and visual
Density  100 cc angular density sampler and total layer sampler
Water content ratio  Dielectric water content ratio meter
Hardness  Push-pull gate, hand test

(4) Backfilling

Although it is hard work to dig an observation pit, it is necessary to backfill it once observation is completed. The wall surface is exposed to the air by excavation, and if it remains so, it can cause changes in the quality of the snow and negatively affect the next observation. This is also necessary to prevent falls into the pit.

Reflections on the research

The Center conducts R&D activities to evaluate the level of risk of snowslides occurring in an environment where global warming is advancing.

Snow cover changes obtained from profile observation are used as valuable basic data (Fig. 1).

(Contact: Snow Avalanche and Landslide Research Center)