Mobile QR Code QR CODE : Journal of the Korean Society of Civil Engineers

  1. Gangneung-Wonju National University (shahn@gwnu.ac.kr)
  2. Member · Mokpo National Maritime University (ckim@mmu.ac.kr)
  3. Member · Gangneung-Wonju National University (Corresponding Author · ghkim@gwnu.ac.kr)



Urban air mobility, Optimal route, Gangneung, Corridor

1. Introduction

Urban Air Mobility (UAM) is an important element of future transport systems. The concentration of urban populations leads to traffic congestion, air pollution, time loss, energy consumption, etc., degrading the quality of urban life. Various innovative transport modes and infrastructures are demanded to solve these problems, among which UAM is noted for its eco-friendliness and ability to travel long distances quickly compared to traditional transport modes.

There has been extensive research on UAM domestically and internationally. To operate UAM, aircraft, vertiports, and corridors are essential. However, research on UAM mainly focuses on aircraft and vertiport. Studies on UAM corridors include GIS analysis for selecting vertiport locations and corridors in Busan (Moon et al., 2023), trends in risk cost model studies for UAM flight path planning (Kim et al., 2024b), transverse corridor standard demonstration study for urban air traffic operation (Kim et al., 2024a), research and development of safety corridor simulation environment for Chungbuk-type UAM using GAZEBO (Lee et al., 2023), researches on the risk of collision or crash of UAM (Kim and Bae, 2023; Kim and Choi, 2022), flight routes establishment through the operational concept analysis of urban air mobility system (Lee et al., 2020) and design and implementation of optimal route and monitoring systems for urban air mobility using mixed reality (Lee, 2022), for UAM Operations though these are significantly less developed compared to studies on aircraft and vertiports.

Cities projected to introduce UAM include large metropolitan areas such as Seoul, Busan, and Daegu, where population concentration and traffic congestion are major issues. However, Gangneung, the area of this study, with a population of about 200,000, is a medium-sized city and the largest city in the Yeongdong region. It becomes a tourist destination with concentrated population during the summer. Gangneung UAM is expected to be utilized not only to solve traffic congestion but also to improve tourism and alleviate transportation exclusion. Additionally, the city expects to introduce UAM aligning with the 2026 ITS (Intelligent Transport Systems) World Congress and the development of MaaS (Mobility as a Service) Station at Gangneung KTX station.

In this paper, a suitable UAM route for flying in the medium-sized city of Gangneung was selected. Safety distances to avoid collisions with high buildings and damage radii for UAM crashes were determined, supporting the research. To carry this out, GIS spatial analysis techniques and three- dimensional visualization were used, analyzing technologies and regulations for UAVs (Unmanned Aerial Vehicles), helicopters, and other systems comprehensively to propose UAM routes. It is hoped that UAM will be successfully introduced in Gangneung City.

2. Research Method

2.1 UAM

To operate UAM, three components are essential: aircraft, vertiport, and corridor (Fig. 1). The aircraft are electric-powered vertical take-off and landing aircraft, similar to helipads, known as eVTOL. The term for the operating and service concept is vertiport, which can be categorized into Vertihub, Vertistop, Vertistation, or Vertistop depending on the number, size, and functionality of the aircraft they accommodate. The flight path for the aircraft is referred to as skyway, corridor, or trajectory. This paper will use the term UAM route.

Fig. 1. UAM, (a) eVTOL (HYUNDAI), (b) Vertiport (NASA), (c) Corridor (Ministry of Land, Infrastructure and Transport)
../../Resources/KSCE/Ksce.2024.44.5.0733/fig1.png

The definition of a UAM route according to the Korean Urban Air Mobility (KUAM) Operation Concept 1.0 is ‘an airspace operated separately for safe UAM operations, through which UAM aircraft travel to their destinations’ (Fig. 2). UAM operates a different system from existing manned or unmanned aerial vehicles. Regional risks and flight standards vary according to the flight route, so it is necessary to fly strictly managed routes rather than freely flying. The following considerations should be taken into account in selecting and designing UAM routes, as described in the operational concept.

Fig. 2. Corridor (Source: Ministry of Land, Infrastructure and Transport)
../../Resources/KSCE/Ksce.2024.44.5.0733/fig2.png

First, reflecting the requirements of the local community and existing stakeholders. Second, meeting the public conditions of local environments, noise, safety, and security. Third, minimizing the impact on Air Traffic Management and Unmanned Aircraft System Traffic Management operations. Fourth, considering the overlap of existing and new corridors and minimizing the impact on flight safety.

Corridors must be designed taking into account the above considerations. Additionally, they are designed for the purpose of traveling to airports and other urban centers, and existing helicopter routes can also be utilized. The flight altitude for UAM is set at approximately 450±150 m above ground level (KUAM Concept of Operations 1.0).

2.2 Research Area

The study area is Gangneung City in Gangwon Special Self-Governing Province, which has been selected by the Ministry of Land, Infrastructure and Transport as a future Mobility as a Service Station (MaaS Station) site (Fig. 3). A future Mobility as a Service Station integrates MaaS, a comprehensive mobility service software offering route optimization, reservation, and payment solutions, with a physical transportation hub called a Station, providing access to various modes of transport such as buses, taxis, rails, and PMs. Gangneung Station, located in the East Coast traffic and tourism hub, is set to enhance the convenience of public transportation for tourists by establishing a transfer center. Furthermore, in conjunction with the World Congress on Intelligent Transportation Systems (ITS) in 2026, there are plans to operate a UAM pilot service in Gangneung as an eco-friendly mobility autonomous sharing city centered around Gangneung Station.

Fig. 3. Gangneung MaaS Station (Source: Gangneung City)
../../Resources/KSCE/Ksce.2024.44.5.0733/fig3.png

2.3 Safe Distance between UAM Aircraft and Building

This study assumes a scenario where a UAM aircraft collides with a building. Equation (1) was used to determine the safety distance required to prepare for a collision between a UAM aircraft and a building.

(1)
$R=k\bullet H$

In Equation (1), $R$ is the safety distance, $H$ is the building height, and $k$ is the proportionality constant which must consider factors such as the size and speed of the aircraft, flight stability, weather conditions, and the density of buildings. However, research on formulas that consider these factors is very lacking at this stage. Therefore, this study proposes assuming proportionality constants based on building height as shown in Table 1. Research on collisions between UAVs and buildings (Pang et al., 2022) indicated that while low-rise buildings, with their high density, presented a greater collision risk, high-rise buildings, with their lower density, had a lower risk of collision. These findings were reflected in the selection of values for the proportionality constant $k$.

Table 1. Proportional Constant Value according to Building Height

Building Height (m)

$k$ $R$ (m)

≤5

2.0

10

5-10

3.0

30

10-15

3.0

45

15-20

1.5

30

20-30

1.0

30

≥30

0.5

15

Fig. 4. Number of Buildings by Height in Gangneung
../../Resources/KSCE/Ksce.2024.44.5.0733/fig4.png

Figure 4 is prepared by extracting building height data for downtown Gangneung, utilizing the GIS Building Integrated Information dataset from V-World. Analysis shows that buildings ranging from 5 to 10 m are most common in Gangneung, a medium-sized city where high-rise buildings over 20 m are scarce. Reflecting the regional characteristics of Gangneung City, proportionality constants were assigned higher values for buildings between 5 to 10 m and 10 to 15 m.

For regulations applicable to UAM flights which are still under research, it is necessary to refer to regulations related to helicopters and UAVs, which share similarities with UAM. According to the regulations of the FAA (Federal Aviation Administration), ICAO (International Civil Aviation Organization), and our Ministry of Land, Infrastructure and Transport (MOLIT), there are regulations concerning the safety distance from structures (Table 2). FAA regulations on helicopter flights (14 CFR Part 91.119) require that aircraft maintain a distance of about 150 m or more from any structure during flight.

Looking at UAV regulations, there are only restrictions on flight altitude and distance from buildings (Table 3). Considering these regulations, it is impossible to select segments where UAM could fly near Gangneung Station. Therefore, this study conducted research by applying safety distances based on building height, based on Equation (1).

Table 2. Regulations on Helicopter Flights Concerning the Safety Distance from Structures

City(m)

Suburban(m)

FAA

300

150

ICAO

300

150

MOLIT

300

150

Table 3. Regulations on UAV Flights Concerning the Safety Distance from Structures

Altitude Limit(m)

Distance Between Buildings(m)

FAA

122

100

ICAO

152

-

MOLIT

150

100

2.4 Risk Radius in Case of Aircraft Crash

This paper conducts research based on the specifications of Hyundai Motor Company’s UAM aircraft, S-A1, which is expected to be introduced in Gangneung UAM. In this study, the risk radius in case of a UAM aircraft crash was calculated using a free-fall model (equation of motion considering gravity and air resistance) that accounts for drag used during the aircraft crash (la Cour-Harbo, 2019). The equation is as follows:

(2)
../../Resources/KSCE/Ksce.2024.44.5.0733/eq2.png

In equation (2), $m$ represents the aircraft weight, $\vec{v}$ represents the velocity vector, and $\vec{g}$ represents the gravitational acceleration vector.

(3)
$c=0.5\rho_{air}AC_{d}$

$c$ is the formula used in fluid dynamics to calculate the resistance force when an object moves through air. $\rho_{air}$ is air density, $A$ is the frontal cross-sectional area of the aircraft, and $C_{d}$ is the drag coefficient. $\rho_{air}$ can vary with temperature and pressure, and $C_{d}$ is a dimensionless coefficient determined by the object's shape, the roughness of its surface, and the state of the fluid's flow. Equation (3) sets out Hyundai's aircraft specifications for determining the risk radius of an aircraft crash as shown in Table 4. The study was conducted assuming the aircraft's weight, frontal area, and maximum speed. The flight altitude was set at the maximum flight altitude of 600 m prescribed in the UAM operation concept document.

Table 4. UAM S-A1 Specification

Specification

Weight

700 kg

Frontal Area

240 m2

Max. Speed

200 km/h

Max. Flight Altitude

600 m

Air Density

1.225 kg/m3

Drag Coefficient

0.5

Using Equation (2) and the UAM specifications from Table 4, the risk radius in case of a UAM crash is approximately 330 m, and the kinetic energy is approximately $4.1\times 10^{6}$ J. Since the exact crash location of a malfunctioning aircraft can be difficult to predict and influenced by various variables, it is assumed that it crashes within the accident risk radius.

In addition to the formula mentioned above, several regulations were checked and used for the study. Applying the 1-1 rule used to set the ground risk buffer in JARUS SORA when analyzing the impact of increased accident risk radius during UAM crash, it is impossible for UAM to fly in the downtown area of Gangneung. The 1-1 rule requires that the aircraft must maintain a ground risk buffer equal to the flying altitude away from populated areas when flying at a certain altitude. With the highest operational altitude of K-UAM being 600 m, this increases the accident risk radius to 600 m (Kim et al., 2022). With the accident risk radius increasing to 600 m, UAM cannot operate at Gangneung Station located in the central downtown area. Therefore, in this study, the risk radius during UAM vehicle crash was set at 330 m and the research was conducted.

3. Gangneung UAM Route

The safety distance between the aircraft and buildings was calculated, and the risk radius in the event of an aircraft crash was determined. The selection of UAM routes was carried out using a GIS spatial analysis method followed by 3D visualization. A digital topographic map of Gangneung city provided by the National Geographic Information Institute, and aerial photographs were used to propose the optimal route for UAM flight (Fig. 5). The data utilized in the research includes a 1:5,000-scale topographic map created in 2023 and orthophotos produced with 25 cm resolution.

Fig. 5. Topographic Map(Left) and Orthophotos(Right) of Gangneung
../../Resources/KSCE/Ksce.2024.44.5.0733/fig5.png

The heights of buildings in Gangneung city were extracted from GIS integrated building information provided by V-WORLD and were modeled in 3D. Structures that did not provide building height data were estimated and modeled accordingly.

Digital maps, DEM (Digital Elevation Model), orthophotos, and building information were projected using the Transverse Mercator coordinate system and underwent overlay analysis. For overlay analysis, buildings were categorized by height (less than 5 m, 5-10 m, 10-15 m, 15-20 m, 20-30 m, over 30 m) and extraction was conducted, and buffer analysis was employed in ArcGIS applying proportionality constants to calculate the safety distance based on building height. This was visualized in 3D using ArcScene as shown in Fig. 6.

Fig. 6. Overlay Analysis Results, (a) GIS Integrated Building Information Provided by V-WORLD, (b) Safety Distance Based on Building Height: Under 5 m(Left), 5~10 m(Right), (c) Safety Distance Based on Building Height: 10~15 m(Left), 15~20 m(Right), (d) Safety Distance Based on Building Height: 20~30 m(Left), Over 30 m(Right), (e) 3D Building Model Generation Using ArcScene, (f) Overlay 3D Building Information and Safety Distance Data
../../Resources/KSCE/Ksce.2024.44.5.0733/fig6-1.png../../Resources/KSCE/Ksce.2024.44.5.0733/fig6-2.png

UAM is considered as a risky mode of transportation due to the potential for crashes; therefore, it is safer to fly over areas like rivers, hills, and seas. For selecting routes, high-traffic roads, multicultural facilities in use by a non-specific majority, large-scale social infrastructure, and comprehensive medical facilities, which are expected to suffer significant casualties, should be excluded from the routes. Additionally, routes considering possible collisions with other aircraft, such as airports and helipads, should be selected.

Gangneung, located adjacent to the East Sea, can utilize the coastal route when flying to other regions in the Yeongdong area, and can use the Namdaecheon in Gangneung to move inland in Gangwon. As a result of comprehensive analysis of these conditions, it was possible to select routes using the coastal route and the river route centered on Gangneung Station vertiport.

In this study, two routes centered around Gangneung Station were selected as shown in Table 5. Safety distances based on building heights were selected as described in section 2.3, and the risk radius of aircraft crash was determined as described in section 2.4 and the data was created into spatial information and analyzed in GIS. The analysis results were visualized in 3D and the route with the lowest risk in the event of an accident was selected. This made it possible to create routes centered around Gangneung Station as shown in Fig. 7.

Fig. 7. Selected UAM Routes
../../Resources/KSCE/Ksce.2024.44.5.0733/fig7.png
Table 5. UAM Routes

Route

Coastal Route

Gangneung Station→Ponam2Dong→

Gyeongpoho Lake→Gyeongpo Provincial Park

River Route

Gangneung Station→Mt. Hwaboo→

City Hall→Namdaecheon

4. Conclusion

Although UAM is considered a next-generation mode of transportation, there is still much research that needs to be done regarding safety. In this study, the safety distances based on building heights were calculated, and the risk radius in the event of an aircraft crash was analyzed using overlay analysis to study UAM routes.

In this study, using GIS spatial analysis methods, the crash impact radius and collision impact radius with buildings were analyzed for a multi-copter type UAM that crashed in the Gangneung area with a span of 15 m, a maximum altitude of 600 m, weighing about 0.7 kg, and moving at about 200 km/h. Based on previous studies and regulations of crash impacts from UAVs, helicopters, etc., spatial information data of the Gangneung area was utilized to identify risk areas due to UAM crashes and to propose routes that are expected to incur minimal damage. The analysis results showed that it is possible to present two routes that involve vertical take-off and landing at Gangneung Station and move through the downtown area of Gangneung. One route utilizes the sea route through Gyeongpo Lake from Gangneung Station, and the other navigates through Namdaecheon near Gangneung City Hall.

There are very few studies conducted on crash radius that could occur in South Korea, so the results of this research are expected to be utilized as a foundation for studies that calculate safety requirements when operating UAM in the Gangneung area or design routes that minimize casualties. Future research considering population density, weather conditions, and traffic volume could become a valuable resource when designing UAM routes in cities other than Gangneung.

Acknowledgements

This research was supported by “Leaders in INdustry- university Cooperation 3.0” and “Regional Innovation Strategy (RIS)” through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE) (2022RIS-005).

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