Establishing Flood Risk Criteria for Vehicles based on Flood Damage Assessment

Ⅰ. Introduction

Recently, localized flood damage in Korea has been occurring frequently due to flash floods and heavy rains linked to climate change, resulting in increased financial losses and loss of life [1],[2]. In areas where flooding occurs due to heavy rainfall, if roads that facilitate the movement of people and goods are submerged, it can lead to mechanical damage to vehicles used in economic activities, as well as pose significant risks to the lives of those traveling in those vehicles [3],[4].

To effectively respond to and mitigate flood damage on roads, it is essential to understand the extent of damage to vehicles. Additionally, preparing for such events requires assessing the potential physical damage and recognizing in advance the level of flooding that could harm vehicles.

According to the report on the analysis of traffic accident characteristics during the summer rainy season in [5], an analysis of flooded vehicles in Gangnam-gu, Seoul, from 2006 to 2012 indicated that flooding occurred when rainfall exceeded 35 mm per hour. Furthermore, during rainfall, the slipping accident rates on highways and general roads were 2.44 and 1.43 times higher, respectively, compared to conditions without rainfall. When a vehicle driving on the road becomes submerged due to flooding, mechanical damage may occur depending on the flooding depth and the location of the vehicle's internal components. In Korea, the Ministry of Land, Infrastructure and Transport (2022) categorizes submerged vehicles into internal combustion engine vehicles and electric vehicles [6]. Kim et al. presented the relationship between submergence depth and damage rate by vehicle type as a relative function, incorporating expert opinions [7]. This information was then used to develop a loss model for assessing the impact of water-related disasters.

To reduce damage caused by flooding, it is important to prepare in advance and provide information about potential flooding before it occurs. If this information is not available, it is essential to recognize the risk of flooding and either take a detour or avoid driving on flooded roads. The Ministry of the Interior and Safety of Korea provides guidelines for vehicle users in their Natural Disaster Action Guidelines [8]; however, these guidelines primarily focus on minimizing casualties.

As previously mentioned, while ensuring safety and preventing loss of life are crucial, the value of assets has also been increasing with societal development. In particular, urban areas experience frequent flooding on roadways, which simultaneously affects both vehicles and their occupants. As of 2023, the number of registered vehicles in South Korea stands at approximately 25.95 million, and this number continues to rise. In densely populated urban areas, the concentration of vehicles is also high, leading to an increase in vehicle damage caused by flooding. However, research on flood damage, particularly focusing on vehicle-related losses, remains limited. Therefore, continuous research is needed to develop effective prevention measures and countermeasures for vehicle-related flood damage.

Therefore, in this study, we select representative vehicles to assess the extent of damage caused by road flooding and evaluate the mechanical damage corresponding to flooding depth. Additionally, we aim to determine the risk of vehicle flooding on the road and establish standards for vehicle exposure during such flooding.

Ⅱ. Selection of Representative Vehicles

There are limitations in assessing flooding damage across all vehicles, particularly in identifying specific heights and affected components. Therefore, this study aimed to select representative vehicles based on their physical characteristics. We chose vehicles that are commonly sold and registered in Korea, as well as those that closely resemble the average vehicle in terms of design. As a result, four types of vehicles were selected as representatives: sedans, SUVs(sports utility vehicle), cargo vehicles, and passenger buses.

The heights of various components for each vehicle were selected and categorized as shown in Table 1. Although there may be slight differences in vehicle heights depending on the type, the locations of these components were assumed to be relatively consistent across the vehicles. When flooding occurs on roadways due to a flood, vehicles are affected by the flow velocity and the depth of the water. However, it is difficult to define the relative size and scale of the flow velocity, and there are limitations in determining the vehicle's speed and condition (on/off) based on flooding. Therefore, these factors were excluded from the analysis.

Table 1.

Classification and maintenance scope according to flooding criteria

Ⅲ. Calculating Flood Damage by Vehicle Type

3-2 Quantification of Mechanical Damage Based on Flood Depth by Vehicle Type

Vehicles consist of approximately 20,000 parts. To establish flooding standards for vehicles, the damage amount associated with the depth of flooding was calculated. The unit prices and quantities of each part for the representative vehicles are organized in Table 2, as presented in Table 1. The number of parts was categorized into approximately 150 items based on part type. Upon investigating the prices of each vehicle's parts, it was found that the total cost of the parts exceeded the vehicle's purchase price. Consequently, if the calculated damage amount exceeded the vehicle's purchase price, the purchase price was used as the flood damage amount.

Table 2.

Number of parts items and unit price per vehicle

Additionally, when flooding occurs, foreign substances and water infiltrate the vehicle's components, leading to a significant reduction in their performance. Therefore, this study assumes that if the floodwater reaches the vehicle's components, the components will be replaced. The replacement cost of the components was then used to calculate the flood damage costs.

Ⅳ. Definition of Flooding Criteria and Risk Levels by Vehicle Type

In this section, the vehicle damage amounts corresponding to flood depth by vehicle type were calculated. The damage amount for each vehicle was determined as the total cumulative cost of the parts based on their locations within the vehicle. Additionally, the extent of damage for each vehicle type was assessed, leading to the definition of flooding criteria and risk levels based on the calculated results.

4-2 Analysis of Crisis Alert and Risk Level by Vehicle Type

The side skirt of a sedan vehicle is located approximately 20 cm above the ground. Normally, when water immersion depths are less than 20 cm, the components at the bottom of the vehicle come into contact with water. Since the interior floor height is around 25 cm, prolonged contact with water significantly increases the risk of rust. Additionally, water entering through the vent between the radiator grille and the hood panel at the front of the vehicle can serve as an inlet to the engine cylinder, potentially causing the engine to stall.

In general, it has been analyzed that the damage level of sedan vehicles increases rapidly at low submergence depths due to their low height and the location of most operational components at the bottom. Table 3 outlines the mechanical damage to sedan-type vehicles based on water depth, as well as the qualitative risk levels related to the maintenance scope presented in Table 1. It was found that 80% of the vehicle sustained damage when the submergence depth reached approximately 100 cm, confirming that serious damage occurs with prolonged submersion.

Table 3.

Mechanical damage and risk level by the flood water depth of sedan

SUV-type vehicles have side skirts positioned about 20 cm above the ground, allowing them to operate even when encountering water due to road flooding below this depth, similar to sedan. However, prolonged contact with water increases the risk of rust. SUVs typically have a higher ground clearance than sedans, with interior flooding occurring at around 45 cm. If water enters the vent connected to the engine at the front, it can cause the engine to stall and result in serious damage to the vehicle.

Additionally, if the flooding depth reaches 66 to 67 cm, approximately the height of the trunk floor, water can infiltrate most major components, leading to significant damage. The mechanical damage and risk levels for SUV-type vehicles evaluated in this study based on flooding depth are presented in Table 4.

Table 4.

Mechanical damage and risk level by the flood water depth of SUV

Tables 5 and 6 present the results of calculating the degree of mechanical damage and the extent of damage based on the flood water depth of vehicle for cargo trucks and buses, respectively. These tables also define the risk levels associated with water depth for each type of vehicle.

Table 5.

Mechanical damage and risk level by the flood water depth of cargo truck

Table 6.

Mechanical damage and risk level by the flood water depth of bus

4-3 Generalization of Risk Level According to the Flood Water Depth of Vehicle

In the case of road flooding, the area below the tire centerline of the vehicle is considered normal driving conditions and can typically be managed with simple maintenance and repairs. However, since the drive shaft is connected to the tire centerline, lubricants within the drive shaft may be compromised due to flooding. Additionally, for flooding above the tire centerline, potential damage to affected components must be assessed. Therefore, while qualitative judgments regarding the depth of flooding and potential damage to vehicle parts are necessary, the risk level associated with flooding depth is comprehensively generalized, as shown in Table 7, based on the information presented in Table 1 and Section 4.2.

Table 7.

Definition of risk level according to the flood water depth of vehicle

Ⅴ. Conclusions

There are numerous assessments of human risk in the event of heavy rain or flooding, but establishing quantitative criteria for asset damage, particularly for vehicles, presents challenges. Therefore, this paper proposes flood risk criteria based on mechanical damage to vehicles during road flooding. Specifically, it assesses the vulnerability of damaged assets by evaluating the degree of mechanical damage to vehicles in relation to flooding depth. First, four types of vehicles commonly sold in Korea were selected, and the degree of mechanical damage was estimated by correlating vehicle parts with specific flooding depths. Based on the calculated results for each type, flooding criteria and risk levels were defined for each vehicle type, leading to a comprehensive generalization of risk levels according to the flood water depth of vehicle.

In this study, vehicle flood risk levels were defined as Level 1 (Attention), Level 2 (Caution), Level 3 (Alert), Level 4 (Severe), and Out of Level (Vehicle Stop), with corresponding flood depths of 10 cm, 25 cm, 30 cm, 40 cm, and 60 cm, respectively. The flood depths for each risk level were defined for four representative vehicles. Among them, the sedan, which has the lowest ground clearance, exhibited the lowest flood depths, while the cargo truck and bus showed similar criteria at Level 1 and Level 2, with flood depths of 10 cm and 30 cm, respectively.

The study confirmed that as flood depth increases, vehicle damage rises sharply, but the rate of damage growth decreases beyond a certain height. Based on these findings, it was concluded that it is essential to quickly evacuate or move out of the flooded area when roadways are inundated.

This study aims to demonstrate that by utilizing the vulnerability of damaged assets and assessing the degree of mechanical damage to vehicles, alongside risk criteria for human safety during road flooding, more effective flood risk criteria can be established. It is expected that the results of this study will be utilized in the future to establish traffic restriction criteria for vehicles during roadway flooding caused by floods, as well as to determine the minimum installation standards for road flooding

Acknowledgments

This research was supported by a grant (RS-2022-ND634021(2022-MOIS61-002)) for the Development Risk Prediction Technology of Storm and Flood for Climate Change based on Artificial Intelligence funded by Ministry of Interior and Safety (MOIS, Korea).

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