Research Trends and Results

Survey of impact of road disasters on traffic andcountermeasure effectiveness
KIMURA Yuji, Senior Researcher
KANEKO Masahiro, HeadMABUCHI Toshiaki, Senior Researcher
Earthquake Disaster Prevention Division, Research Center for Disaster Management(Key words) Road disaster prevention countermeasures, impact on road traffic, road disaster prevention inspection
items, evaluating countermeasure effectiveness

Road arrival distance (m)
道路到達距離(m)

20.0
18.0

θ=45°
θ=40°

Zone [3]ゾーン③

桃色：崩壊深さ3m

Orange: collapse depth 3m
水色：崩壊深さ1m
16.0 Light
blue: collapse depth 1m
14.0θ=35°

12.0

θ=30°

10.0

θ=45°
θ=40°
θ=35°
θ=30°

Zone
[1]
ゾーン①

8.0
6.0

4.0
2.0

Zone
[2]
ゾーン②0.00

1020

Set as slope and road
7m apart and road widthof 6m (3m×2 lanes)

30
40
50
Averageslope height (m)
平均斜面高さ(m)60

70Figure 1. Relationship of Average Slope Height withRoad Arrival Distance
Next, the relationship of the quantity of collapsed
soil with the road closure time in past disaster cases
was organized by selecting 54 cases from pastdisasters on national government operated roads
throughout Japan, revealing that although scattered, as
the approximate quantities of collapsed soil increases,
the length of time the road is closed tends to increase(Fig. 2).
40,00035,000closure time (min.)Road
通行止め時間（分）1. Introduction
Road managers work to implement efficientcountermeasure projects with limited budgets based on
documents such as the results of comprehensive
inspections of road disaster prevention, in order tomaintain and manage roads in ways appropriate to theharsh natural conditions found in Japan. This survey
collected and analyzed cases of disasters caused byroad slope disasters to organize conditions that causeroad disasters at the same time as it studied a methodof evaluating the impacts of road disasters on roadtraffic and the effectiveness of road disasterprevention countermeasures, in order to provide
information that will contribute to the efficient
implementation of disaster prevention countermeasureprojects
2. Estimating distances to roads and evaluating
impact on traffic
To study the impact of road slope disasters on
traffic, the relationship between the state of occurrenceof disasters and road disaster prevention inspection
items on roads operated by the national government
from 1990 to 2004 was organized, and an effort wasmade to use an existing formula1)to calculate the soil
traveling distance at two locations where it ishypothesized based on the organized conditions that acomplete road closure would occur, revealing that in
all cases, the discharged soil would cover the entire
road surface.
The above formula was used to calculate thedistance the discharged soil would travel to reach theroad and at the same time, its impact on closure of theroad to traffic was evaluated considering the roadwidth, and the distance between the slope and the road(Fig. 1). The result reveals that at slope height of 20m
or less, regardless of the depth of the collapse (zone[1]), and even at slope height higher than 20m, atcollapse depth of 1m or less (zone[2]), the collapsed
soil would stop by one lane of the road.

30,00025,00020,00015,00010,000
5,000
00

2,000

4,000

6,000

8,000

10,00012,00014,00016,000

流出土砂量（ｍ3）
Quantity ofdischarged soil (m3)Figure 2. Organization of Relationship of Quantityof Discharged Soil with Traffic Closure Time
3. Evaluation of countermeasure effectiveness
From the disaster cases selected in 2 above,
focusing on the quantity of soil reduced bycountermeasures, the state of appearance of effects ofvarious countermeasure works and the reduction of thequantity of soil that can be counted on to occur wereorganized. As examples, for “protective net works”
and “safety barrier works + revetment works”, it wasobserved that they do prevent some of the soil frombeing discharged onto the road, but in the case of ahuge quantity of soil that would cover the entire roadsurface, it is impossible to capture it all. So to selectcountermeasure work methods, it is considered to benecessary to also consider adding conditions such as
the estimated quantity of collapsed soil shown in 2, its
impact on traffic, etc.
4. Summary
Methods of estimating the scale of a disaster and its
impact on road traffic, selecting countermeasure
works, and evaluating the effectiveness of the works
were successfully studied by collecting and analyzingcases of road slope disasters. In the future, we will
analyze cases focusing on topographical andgeological conditions for example to continue to study
the improvement of the method and its applicability tovarious types of locations.
[Sources]
1) Notification stipulating the method etc. that theMinister of Land, Infrastructure, Transport and Tourism
stipulates based on the provisions of Article 2 item (2) ofthe Enforcement Order of the Act on Sediment Disaster
Countermeasures for Sediment Disaster Prone Areas,
2001