Sehyun Tak

• Doctor of Philosophy
• Researcher at Korea Advanced Institute of Science and Technology

Recently, with growing interest in urban mobility patterns, the demand for collecting and analysing origin‐destination (OD) data is increasing. Due to the large scale and dimensionality of OD data, there are two issues in analysing the data: big‐data storage and major pattern extraction. To deal with two issues at the same time, this study suggests...

Bus rapid transit (BRT) system is a cost‐effective way to provide public transportation service. However, it faces some challenges such as reduced labour productivity and increasing fuel costs. One solution is introducing automated vehicles (AV) to reduce operational expenses. However, there are still limitations on completely replacing human drive...

In addition to addressing the labor shortage due to an aging population, the transition to autonomous vehicle (AV)-based mobility services offers enhanced efficiency and operational flexibility for public transportation. However, much of the existing focus has been on improving AV safety without fully considering road conditions and real-world serv...

This paper attempts to solve the problem of identifying the critical factors of road design on human driver (HD) accidents and automated vehicle (AV) failures. This study is of immediate importance for the safety of the road, which must facilitate the wide emergence of commercialized vehicle automation technologies. We overcome the weakness of the...

Nowadays, Automated Vehicle (AV) technology is gaining attention as a candidate to improve the efficiency of Bus Rapid Transit (BRT) systems. However, there are still some challenges in AV technology including limited perception range and lack of cooperation capability in mixed traffic situations with drivers. The emerging Connected and Automated V...

There have been enormous efforts to develop a novel vehicle routing algorithm to reduce origin-to-destination (OD) travel time. Most of the previous studies have mainly focused on providing the shortest travel time route based on estimated traffic information. Few researches have considered the use of predictive information on traffic dynamics to i...

The safety of urban transportation systems is considered a public health issue worldwide, and many researchers have contributed to improving it. Connected automated vehicles (CAVs) and cooperative intelligent transportation systems (C-ITSs) are considered solutions to ensure the safety of urban transportation systems using various sensors and commu...

There have been enormous efforts to implement automated vehicle-based mobility (AVM) by considering smart infrastructure such as cooperative intelligent transportation system. However, there is lack of consideration on economical approach for an optimal deployment strategy of the AVM service and smart infrastructure. Furthermore, the influence of t...

Various mobility services have been proposed based on the integration of automated vehicle (AV) and road infrastructure. Service providers need to identify a set of road sections for ensuring the driving safety of an AV-based mobility service. The main objective of this research is to analyze the safety performance of AVs on the road geometrical fe...

The safety of urban transportation systems is considered a public health issue worldwide, and many researchers have contributed to improving it. Connected automated vehicles (CAVs) and cooperative intelligent transportation systems (C-ITSs) are considered solutions to ensure urban transportation systems' safety using various sensors and communicati...

When attempts are made to incorporate shared autonomous vehicles (SAVs) into urban mobility services, public transportation (PT) systems are affected by the changes in mode share. In light of that, a simulation-based method is presented herein for analyzing the manner in which mode choices of local travelers change between PT and SAVs. The data use...

The modeling of walking behavior and design of walk-friendly urban pathways have been of interest to many researchers over the past decades. One of the major issues in pedestrian modeling is path planning decision-making in a dynamic walking environment with different pedestrian flows. While previous studies have agreed that pedestrian flow influen...

Vehicular collision and hazard warning is an active field of research that seeks to improve road safety by providing an earlier warning to drivers to help them avoid potential collision danger. In this study, we propose a new type of a collision warning system based on aggregated sectional information, describing vehicle movement processed by a roa...

A previously developed real-time forward collision warning system (RCWS) using a multi-layer perceptron neural network (MLPNN) with a single hidden layer aims to be implemented with in-vehicle sensor and smartphone under cloud-based communication environment. However, several issues exist concerning the communication delay between the smartphone an...

Various collision avoidance systems (CASs) have been developed and employed in human-operated vehicles as well as more recently in autonomous vehicles. Most of the existing CASs perform an override function to actuate automatic emergency braking in a critical situation based on the current traffic information obtained from in-vehicle sensors or sho...

The introduction of autonomous vehicles (AVs) in the near future will have a significant impact on road traffic. AVs may have advantages in efficiency and convenience, but safety can be compromised in mixed operations of manual vehicles and AVs. To deal with the issues associated with mixed traffic and to avoid its negative effects, a special purpo...

In perimeter control, model predictive approaches have performed well in previous studies, but they were done in a centralized way. Considering real-time feasibility, extensibility, and functional stability, a distributed approach could be a promising solution particularly for cases with a large number of networks. In this paper, a new distributed...

Ideal configuration or layout of highways should resemble the actual demands for the roads represented by Origin-Destination (OD) information. It would be beneficial if existing highways can be evaluated for their configurational fitness against the current demands, and newly planned highways can carefully be designed in terms of their layouts and...

Surrogate Safety Measure (SSM) is one of the most widely used methods for identifying future threats, such as rear-end collision. Various SSMs have been proposed for the application of Advanced Driver Assistance Systems (ADAS), including Forward Collision Warning System (FCWS) and Emergency Braking System (EBS). The existing SSMs have been mainly u...

The field of research that has recently come to the fore is the perimeter control, which aims to control traffic demand for a large urban area prior to controlling internal flow inside the area. Such control concept needs to be tested by simulations, hence, it is necessary to develop a model that can appropriately estimate the network-wide flow dyn...

The aim of the concept of perimeter control is to manage the transfer flow between urban road networks. However, there is a lack of description on the behavior of transfer flow between networks in relation to the macroscopic fundamental diagram (MFD). Hence, this paper suggests a description of transfer flow and investigates it with microscopic sim...

The human factor in the current railway system is a dominant cause of collision accidents. There exists a degree of uncertainty to the train driver on the timing of decision-making. Mitigating collision risks that are associated with the uncertainty of driving behavior is a challenging task. In this paper, we propose a train-simulator that incorpor...

Building-integrated photovoltaics (BIPV) are one of the most important sustainability technologies for building energy, and the semi-transparent solar cell is one of the most promising photovoltaic systems for building integration because it can generate electricity and is transparent with a range of beneficial optical properties. On the other hand...

To improve the safety and capacity of traditional Track-Based Train Control (TBTC) System, Communication-Based Train Control (CBTC) system has been proposed. In the previous researches, the CBTC system not only improves the line capacity of the railway but also enhances the safety with continuous wireless communication. However, these improvements...

Understanding the patterns of crowd movement for evacuation is essential to design public infrastructure and building with high level of safety and serviceability. However, observing and describing the dynamics of pedestrian evacuation is a challenging issue. Many related studies have been conducted in both microscopic and macroscopic views. Micros...

In the intelligent transportation system field, there has been a growing interest in developing collision warning systems based on artificial neural network (ANN) techniques in an effort to address several issues associated with parametric approaches. Previous ANN-based collision warning algorithms were generally based on predetermined associative...

Safety warning systems generally operate based on information from sensors attached to individual vehicles. Various types of data used for collision risk calculation can be categorized into two types, microscopic or macroscopic, depending on how the sensors collect the information of traffic state. Most collision warning systems use only either of...

Travel time prediction is one of the most important components in Intelligent Transportation Systems implementation. Various related techniques have been developed, but the efforts for improving the applicability of long-term prediction in a real-time manner have been lacking. Existing methods do not fully utilize the advantages of the state-of-the...

Missing data imputation is a critical step in data processing for intelligent transportation systems. This paper proposes a data-driven imputation method for sections of road based on their spatial and temporal correlation using a modified k-nearest neighbor method. This computing-distributable imputation method is different from the conventional a...

A vehicle traffic predictive cruise control (TPCC) system, responding to the change of downstream traffic situation, has been proposed to improve traffic operation and the fuel efficiency of vehicle based on the asymmetric traffic theory. The proposed predictive cruise control system consists of four parts: 1) deceleration-based safety surrogate me...

Prediction of origin-destination (O-D) demand is an important topic in transportation engineering because it is a crucial input for a dynamic traffic management and control system. Previous literature has focused primarily on estimation and prediction of O-D demand with Kalman filtering; however, these forecasts lack efficiency when unusually fluct...

An automated vehicle controls its throttle and brake systems on the basis of the spacing policy, which is used to control the distance between vehicles. The spacing policy is required for maintaining a desirable state of vehicle movement in consideration of the movement of preceding vehicles. Because a spacing policy significantly influences the pe...

1 Understanding the patterns of crowd movement for evacuation is essential to design public 2 infrastructure and building with high level of safety and serviceability. However, observing and 3 describing the dynamics of pedestrian evacuation is a challenging issue. Many related studies have 4 been conducted in both microscopic and macroscopic views...

The government of South Korea has made great efforts in the area of railway safety management by means of a railway safety law and an integrated railway safety plan established in 2004 after the Daegu subway fire accident. However, after certain railway incidents, a reactive railway safety management system has been implemented that has led to fata...

A surrogate safety measure can be used for preventing hazardous roadway events by evaluating the potential safety risk by using information on the driving environment gathered from vehicles. In this paper, the deceleration-based surrogate safety measure (DSSM) is proposed as a safety indicator for rear-end collision risk evaluation based on the saf...

Travel time is one of the most required traffic information for both individual travelers and road system authorities. So, many researchers have developed several techniques for travel time prediction. However, most of the existing methods have been focusing on predicting travel time on highways, whereas developing methods particularly for urban ro...

The dye-sensitized solar cell (DSSC) is recently attracting tremendous interest as a green and renewable energy conversion device. The DSSC is one of the promising alternatives to inorganic photovoltaic devices as it can generate electricity with low production cost, which is about 1/5 of the production cost for Si based solar cells, and relatively...

Estimating and predicting the travel time on freeways with reasonable accuracy is essential for successful implementation of an intelligent transportation system. However, the related previous studies have some problems. The statistics-based methods have problems in accuracy, and some others are limited to predicting the travel time only during sho...

Current safety warning systems generally operate based on the information from sensors attached to individual vehicles. This vehicle sensor-based system can only estimate the collision potential situation in close proximity of a subject vehicle, and it requires additional communication technologies such as Vehicle-to-Vehicle (V2V) and Vehicle-to-In...

A vehicle Predictive Cruise Control system has been developed to improve the fuel efficiency of vehicle and traffic flow performance based on the asymmetric traffic theory. The Predictive Cruise Control system consists of fourparts: (1) Deceleration-based Safety Surrogate Measure, (2) Adaptive Cruise Control, (3) Multi-Vehicle Measurement, and (4)P...

Maintenance optimization based on life cycle cost (LCC) assessment is applied to many civil infrastructure systems such as pavements and bridges to reduce operating and socioeconomic cost. However, due to the large size of infrastructure networks, maintaining such networks is challenging, especially when many constraints exist and the budget is lim...