PyBTLS: A Python-C++ open-source package for traffic load simulation on short-to-medium span bridges

Traffic loading information is a critical step in bridge design code calibration and bridge assessment. Since the anticipated lifetime of bridges is typically quite long (e.g., 100 years), direct traffic measurements are insufficient to fully understand the extremes of the phenomenon. Therefore bridge traffic load simulation offers the best way to utilise and extend limited traffic datasets to larger, more representative databases, and observe extremes. However, bridge engineers and researchers currently lack a generally available state-of-the-art tool capable of performing this task effectively. PyBTLS (Python Bridge Traffic Load Simulation) is an open-source Python-C++ package designed to address this gap. It is the culmination of over two decades of work in the field. It allows users to efficiently generate a wide range of traffic flow scenarios, compute corresponding bridge load effects using influence lines or surfaces, and perform common data processing in bridge engineering. PyBTLS adopts a hybrid Python-C++ architecture using pybind11 , with C++ serving as the high-performance simulation core and Python providing the interface to simplify and automate user interactions. Its modular object-oriented design facilitates both maintainability and extensibility. PyBTLS is expected to make a meaningful contribution to the work of bridge engineers and researchers, particularly in tasks related to traffic load modelling, bridge evaluation, and design code calibration.