Design of a structure free intersection controller for connected bicycles and cars using model based control and a genetic algorithm

Abstract

Bicycles have an important role to play in the transition towards a more sustainable mobility. In order to achieve the modal shift towards bicycles, more must be done to accommodate cyclists. Although controlled intersections do increase the (perceived) safety of crossings with motorized vehicles, they are seen as major obstacles, and cyclists tend to avoid them when possible. The negative effects of controlled intersections for cyclists may be reduced by new methods of intersection control. This thesis combines the concepts of the connected environment and structure free control, to design an intersection controller that uses a genetic algorithmto determine the optimal signal plan, hereafter referred to as the SFGA controller. The controller is designed for an isolated intersection and considers car drivers and cyclists. Desires of cyclist with regard to controlled intersections, are identified by means of a literature review on the determinants of bicycle use, which are then projected on the controlled intersection. A traffic system model, based on validated models found in literature, is set up and a design for the structure free controller is proposed. A set of control objectives is proposed, including different metrics related to the desires of cyclists and car drivers. Objective function weights can be varied to achieve different levels of cyclist prioritization. A maximumwaiting time of 100 seconds is enforced in order to prevent prioritization of cyclists to result in unreasonable delays for car drivers, because red light running probabilities increase at larger waiting times. The performance of the structure free controller is evaluated for 15, 35 and 45% traffic saturation (percentage of intersection capacity), by means of a simulation based case study. The designed controller is benchmarked to vehicle actuated control (VA). VA has a cyclic, fixed control structure in which green times of movements are flexible and depend on the queue size. SFGA is benchmarkedwith an equalweight for the delay of car drivers and cyclists, and no weight included for the number of stops. The effect of incorporating weights that prioritize the desires of cyclists over those of car drivers is investigated. The SFGA controller results in average delays 1.8, 2.7 and 3.0 times lower than VAC for each of the evaluated traffic saturation levels. The number of stops is 1.9, 2.3 and 3.1 times lower. Including weights in the objective function to explicitly prioritize cyclists, results in even lower average delays and number of stops for cyclists. As is to be expected, this comes at the cost of additional delays for car drivers, especially for higher traffic saturation. The better performance of SFGA is attributed to two main differences between the controllers. First of all, the structure free aspect allows for a larger degree of freedom to choose more effective combinations of traffic lights to show green at the same time, instead of following the fixed sequence of VA. Additionally, the controller allows traffic that otherwise would experience the largest total delay to cross first, even if this means delaying some travellers in close proximity of the traffic light. This contrary to VA, that extends green time based on detected traffic in the active block. Without inclusion of weights that prioritize the desires of cyclist over cars, the controller already tends towards prioritization of the cyclists. This is caused by the controller considering the number of travellers that are influenced by its’ control decisions, combined with the higher traffic densities, that can be expected on bicycle paths in urban areas. Weights to prioritize cyclists can be included to include more priority, for example when bicycle traffic volumes are low. This work implicates that, in order to better serve the cyclists, it is not explicitly required to prioritize cyclists over cars. In areas with large volumes of cyclists, considering the number of travellers and their proximity to the traffic light can already result in cyclists being served better. This work could be used as a starting point or inspiration to design and eventually implement more cyclist oriented intersection controllers. Improvements for the controller and extensions for the research scope are proposed that are required for the controller to be suitable for practical implementation in the real world. If a future version of the controller is to be implemented, it will reduce the negative effects of controlled intersections on cyclists, thereby making the bicycle a more suitable replacement for the car.