Low-emission alternative bus technologies are of increasing interest to bus fleet operators due to the reduced environmental impact and potential for lower operating costs. However, with uncertainty regarding the total cost of ownership of new technologies and life cycle impacts beyond the typical well-to-wheel boundary, stakeholders may not have the necessary specific tools or evidence to evaluate life cycle impacts. The aim of this paper is to develop a novel framework to assist decision-makers in assessing the uncertainty of the life cycle impacts of alternative bus technologies. The Technology Impact Forecasting methodology was employed, integrating a life cycle model, to investigate whole life cycle impacts in an exploratory assessment environment, allowing for the analysis and trade-off evaluations of alternative drivetrain technologies and operational scenarios. This research provides a comprehensive novel framework for addressing uncertainty in whole life cycle costs and GHG emissions for the manufacture, use, maintenance and infrastructure phases of diesel and battery electric buses. Eleven scenarios are assessed in the framework, evaluating combinations of battery technologies, well-to-tank pathways, charging infrastructure and auxiliary demands. For every battery electric bus scenario, there is an 80% confidence that life cycle GHG emissions are mitigated by 10–58% compared to the baseline diesel bus, but life cycle costs are 129–247% higher. Opportunity charged electric buses employing a lithium-titanate battery are the most effective scenario for mitigating GHG emissions per additional cost of the new technology to the operator. The framework highlights a key trade-off between dependence on battery capacity and high-power charging infrastructure for battery electric bus technologies. The framework enables stakeholders to make technology adoption and resource allocation decisions based on the risk of a scenario and provides a level of confidence in a technologies’ ability to mitigate whole life cycle impacts.