The traffic congestion, which has become one of the major problems of developed and developing countries, has led to a shift in the way public transport systems are viewed, and it has accelerated efforts to increase the efficiency of these systems. In recent studies, several approaches, in which both user and operator benefits are evaluated together in order to increase the demand for public transportation systems and to ensure the sustainability of these systems, are emphasized. In this study, a bilevel simulation/optimization model is developed to optimize service headways and departure times of first buses from the beginning of the routes in urban bus networks. At the upper level of the proposed model, a multiobjective function representing user and operator costs is evaluated using the metaheuristic harmony search (HS) optimization technique. The transit assignment problem, which represents the distribution of transit users over the routes, is handled at the lower level. In the proposed model, the transit assignment problem is solved by the timetable-based assignment approach with VISUM transport planning software. The timetable-based transit assignment is an approach in which the perception errors within the users’ route choice are taken into consideration and the transfer wait times can be precisely calculated. The proposed model is applied to a real-life urban bus network of the Çorlu district (Tekirdağ, Turkey), and the effectiveness of the model on a medium-sized urban bus system has been demonstrated. The results show that the user and operator benefits can be simultaneously increased by adding an initial departure offset parameter to the problem.

Gelişmekte olan ülkelerde kentiçi toplu taşıma sistemleri arasında en yaygın tür olan otobüs taşımacılığının verimliliğini arttırmaya yönelik çalışmalar son yıllarda artmaktadır. Otobüs sitemlerinin performansının ele alındığı birçok çalışmada, kullanıcı ve işletmeci faydalarını eniyileyen yaklaşımlar üzerinde durulmaktadır. Bu çalışmada, kentiçi otobüs ağlarındaki sefer sıklıklarını eniyileyen ikiseviyeli bir simülasyon/optimizasyon modeli geliştirilmektedir. Üst seviyede, işletmeci ve kullanıcı maliyetlerini temsil eden bir amaç fonksiyonunun çözümü için sezgisel Armoni Araştırması (AA) optimizasyon tekniği tabanlı bir model önerilmektedir. Alt seviyede ise talebin toplu taşıma ağına dağılımını temsil eden toplu taşıma ataması problemi çözülmektedir. Önerilen modelde, aktarma bekleme sürelerinin kesin hesabı için zaman çizelgesi tabanlı toplu taşıma ataması yaklaşımı kullanılmakta ve toplu taşıma ataması problemi logit tabanlı bir modele dayalı olarak VISUM yazılımı ile çözülmektedir. Geliştirilen model, toplu taşıma ağ tasarımı çalışmalarında yaygın olarak kullanılan bir test ağına uygulanmıştır. Sonuçlar, AA tabanlı modelin sefer sıklığı optimizasyonu probleminin çözümünde etkin olarak kullanılabileceğini ortaya koymuştur.In developing countries, efforts to increase the efficiency of bus transportation, which is the most common type of urban public transport systems, have been increasing in recent years. Many studies addressing the performance of bus systems focus on approaches to optimizing user and operator benefits. In this study, a bi-level simulation/optimization model is developed to optimize service frequencies in urban bus networks. At the upper level, a meta-heuristic Harmony Search (HS) optimization technique based model is proposed for solving an objective function that represents operator and user costs. At the lower level, the transit assignment problem, which represents the distribution of demand over the transit network, is solved. In the proposed model, a time-table based transit assignment approach is used for the exact calculation of transfer wait times, and the transit assignment problem is solved using VISUM software based on a logitbased choice model. The developed model has been applied to a test network that is widely used in transit network design studies. The results show that the HS based model can be used effectively to solve the service frequency optimization problem.