Eungcheol Kim

Genetic Algorithm-Based Approach for Optimal Location of Transit Repair Vehicles on a Large Urban Network

Determining the optimal location of a fleet of vehicles is necessary in a number of potential applications, such as special repair vehicles for buses on a large public transportation network. The Athens Urban Transport Authority operates a large bus fleet over an extensive network for 19 h a day and serves a population of approximately 4 million people, all in a heavily congested road network. During the 2004 Summer Olympic Games, held in Athens, most spectators, employees, and volunteers were transported to and from Olympic Games venues by public transportation. Dedicated Olympic Games bus lines operated under a tight around-the-clock schedule. During normal operations and particularly during events such as the Olympic Games, incidents such as vehicle breakdowns and minor accidents can have a severe effect on the operation of the public transport network and can cause a significant decrease in the level of service. To help the authority locate bus repair vehicles over the entire network, a decision support system was developed on the basis of an embedded genetic algorithm used for obtaining optimal location solutions. The systems design and performance make it easy to operate under real-time conditions, which is useful for planning and for fast vehicle redeployment.

Development of Real-Time Optimal Bus Scheduling and Headway Control Models

Infrequent bus service because of a sudden rise in international gas prices has created a significant social problem in South Korea. Bus service frequency is determined by considering bus operation costs to the service supplier, passenger demand, and so forth. Optimal bus frequency was determined and a timetable for each bus stop was created by applying the DTR (demand- and travel time–responsive) model or the DTRC (demand- and travel time–responsive model for critical scheduling areas); both use data for each bus stop and route segment. A bus headway control model that can monitor and assess punctuality of an operation was also developed. This model was based on real-time event data, such as bus stop departures and arrivals for buses operating on a line-based timetable, constructed for each bus stop. It was also based on the bus stop traffic cost, which was applied in the bus scheduling model. The models ability to evaluate the punctuality of operation made it possible to transmit headway control instructions (when to decelerate or accelerate) to a bus driver via an onboard unit. A model verification process was implemented by using data collected from a bus management system and integrated transit fare card system for the bus route in Seoul. To evaluate the reliability and uncertainty of the optimal solution, a sensitivity analysis was implemented for the various parameters and assumptions used in the models.

Comparison of Vertical Alignments for Rail Transit

AbstractIn this paper two vertical alignment profiles (labeled dipped and undipped) connecting rail transit stations with different elevations are compared. A deterministic simulation model is developed and used to analyze train motion and energy use for three different vertical alignments. To minimize the cost of rail transit operation for both directions, cruising speed is optimized as a decision variable while train operations are simulated on the proposed vertical alignments. The numerical analysis and sensitivity studies show that the developed deterministic simulation model is useful for comparing vertical alignments, and that the proposed alignment concepts can significantly reduce travel time, energy use, brake wear, operating cost, and total cost compared with the baseline alignment profile.

Estimating Highway Earthwork Cross Sections by Using Vector and Parametric Representation

Two methods are introduced for using vector and parametric representation for precisely estimating cross-sectional areas for highway earthwork. Accurate estimation of cross-sectional areas can minimize errors in the total earthwork cost calculation. The vectors and the parametric representation are used to describe mathematically any referencing point along a cross section. Two methods by which to calculate cross-section earthwork areas—proportionally weighted interpolation and planar interpolation—are developed and are based on the cases most likely to be encountered. These methods can supply precise earthwork cost estimates to highly automated alignment optimization processes. An example study shows that the proposed methods give more-precise results than do the existing methods. The proposed methods not only are simple but also have important advantages in automation, ease of handling, and good adaptability to highway alignment optimization algorithms.

Simulation-Based Rail Transit Optimization Model

A proposed bilevel optimization process determines the depth of a dipped vertical alignment between rail transit stations as well as the cruising speed for each direction. This model also considers how regenerative braking may affect vertical alignment decisions. The optimized depth and directional cruising speeds were jointly obtained in a numerical example. A sensitivity analysis showed that regenerative braking reduced the total cost but did not significantly change the optimized depth of the dipped vertical alignment. The developed model is more realistic and useful than previous ones because it allows unequal station elevations, jointly optimizes decision variables, and considers regenerative braking.

Critical aggressive acceleration values and models for fuel consumption when starting and driving a passenger car running on LPG

ABSTRACT The models based on vehicle speed have been used to estimate fuel consumption and CO2 emissions. However, these models could not properly estimate the change in fuel consumption and CO2 emissions as the speed changes. As for the alternative method, people try to consider using acceleration instead of speed. Although acceleration has been seriously considered, determining critical aggressive acceleration value in relation to fuel consumption and CO2 emissions is difficult to find. In this study, evaluation models of fuel consumption were developed using instantaneous acceleration, and we defined the critical aggressive acceleration values for different states of the vehicle from the viewpoints of fuel consumption and emissions. We used a mid-sized Liquefied Petroleum Gas (LPG) passenger car and obtained instantaneous data from a digital tachograph installed in the car while it accelerates. We developed two fuel consumption models and found critical aggressive accelerations, respectively: a model of starting vehicle that measures range of speed required to overcome the inertia during acceleration from stop state, and the other model for the driving state. We used Classification and Regression Tree (CART) analysis to find the critical aggressive accelerations at which the increments of fuel consumption change abruptly. As a result, the critical aggressive accelerations causing abrupt change in the increments of fuel consumption were found to be 2.598 m/s2 for the starting of vehicles and 1.4705 m/s2 when driving them. We also found that the increments of fuel consumption can be explained through quadratic and exponential functions with instantaneous acceleration.

A Sensitivity Analysis of Critical Genetic Algorithm Parameters: Highway Alignment Optimization Case Study

Genetic Algorithms GAs have been applied in many complex combinatorial optimization problems and have been proven to yield reasonably good solutions due to their ability of searching in continuous spaces and avoiding local optima. However, one issue in GA application that needs to be carefully explored is to examine sensitivity of critical parameters that may affect the quality of solutions. The key critical GA parameters affecting solution quality include the number of genetic operators, the number of encoded decision variables, the parameter for selective pressure, and the parameter for non-uniform mutation. The effect of these parameters on solution quality is particularly significant for complex problems of combinatorial nature. In this paper the authors test the sensitivity of critical GA parameters in optimizing 3-dimensional highway alignments which has been proven to be a complex combinatorial optimization problem for which an exact solution is not possible warranting the application of heuristics procedures, such as GAs. If GAs are applied properly, similar optimal solutions should be expected at each replication. The authors perform several example studies in order to arrive at a general set of conclusions regarding the sensitivity of critical GA parameters on solution quality. The first study shows that the optimal solutions obtained for a range of scenarios consisting of different combinations of the critical parameters are quite close. The second study shows that different optimal solutions are obtained when the number of encoded decision variables is changed.

Developing Bike Road Design Alternatives Considering Land Use Characteristics

The Korean government recently has focused on variety of policies to promote the use of bikes to control the emission of carbon. However, bike facilities with no regard to the safety and comfort of bike drivers has made inefficient bike roads. Also, the accidents related to bikes have increased rapidly. This study proposes the proper types of the bike roads considering land use and bike driver characteristics. The elements classifying the bike driver characteristics are driven through oneway ANOVA and cluster analysis. It is found that the types of the bike roads can be classified by the ratio of child and elderly bikers and the ratio of heavy trucks. Also, the each type is characterized by the land use types such ad residential, commercial and industrial areas through cluster analysis. According to the results of the cluster analysis, installation of bike roads in residential area needs to consider convenience and safety simultaneously. It is also found that convenience should be the most considerable factor in commercial area. Lastly, safety should be considered in industrial area. Recommended methodology and bike road type based on the land use and bike driver`s characteristics can be useful to develop bike-friendly environments and increase mode share of bikes.

Switching service types for multi-region bus systems

ABSTRACT Conventional fixed-route bus services are generally preferred to flexible-route services at high demand densities, and vice versa. This paper formulates the problem of integrating conventional and flexible services that connect a main terminal to multiple local regions over multiple time periods. The system’s vehicle size, route spacing (for conventional services), service area (for flexible services), headways and fleet sizes are jointly optimized to minimize the sum of supplier costs and user costs. The route spacing for conventional bus services and service area for flexible bus services are also optimized for each region. The proposed solution method, which uses a genetic algorithm and analytic optimization, finds good solutions quickly. Numerical examples and sensitivity analyses confirm that the single fleet variable-type bus service may outperform either the single fleet conventional bus service or the single fleet flexible bus service when demand densities vary substantially among regions and time periods.

Development of a Korea highway safety evaluation proto type model on the concept of IHSDM crash prediction module

This study tries to develop a Korea highway safety evaluation proto type model for quantified safety evaluation. We develop a base model and crash modification factors (CMFs) through reviewing the procedures and methodologies in Highway Safety Manual. At the same time, we try to carefully consider collectable data and roadway environment of Korea that are different from the USA. CMFs are developed through models and experts judgement. Developed CMFs are for driveway density, pedestrian crosswalk, existence of median, terrain types, and land-use types. Also, verification of the developed base model and CMFs were performed using two routes of Koreas rural two-lane highways while comparing with roadway safety design synthesis and Crash Prediction Module (CPM) of Interactive Highway Safety Design Model (IHSDM). Applicability analysis was then performed in two aspects of predictability and adaptability of the proto type model. As a result, CMFs and predicted accident estimates of CPM are similar with the developed Korea proto type model. However, the base model and CMFs of the developed proto type for Korea are more precise than the others when evaluating sections where the number of actual accidents is higher. It is found that considering CMF for land-use type is justifiable when developing a Korea highway safety evaluation proto type model. This study validates the possibility of developing a full scale of Korea highway safety evaluation model.