Open-source software development is becoming increasingly popular in the public sector due to its potential for innovation and technology integration. This study investigates the possibilities of developing an open-source trip planner using OpenTripPlanner (OTP) for the Uppsala region’s growing public transport needs. This thesis aims to increase understanding of the opportunities and challenges of open-source software development within the public sector and what lessons can be learned from previous implementations of OTP. The methods used were the development of a stand-alone web-based Proof of Concept of an OTP solution as well as a case study including public organizations that have worked with open-source software development and specifically implementations of OTP. The implementation of the Proof of Concept shows the work effort put in to set up a web-based OTP solution, how it can be used and adapted to the Uppsala region’s needs. The results from the case study show that open-source applications can be developed through cooperation within and between regions and countries, resulting in innovative solutions with more transparency and flexibility. The use of OTP has the potential for creating a less complex, streamlined system with flexible and efficient data processing. Challenges include the administration of the data sets used, changing the work culture to more open ways of working and understanding ones needs to develop the right product. The need for a comprehensive system review and the establishment of competent teams or suppliers are identified as critical factors in successful open-source development.