  Participatory Budgeting (PB) has evolved into a key democratic instrument for
resource allocation in cities. Enabled by digital platforms, cities now have
the opportunity to let citizens directly propose and vote on urban projects,
using different voting input and aggregation rules. However, the choices cities
make in terms of the rules of their PB have often not been informed by academic
studies on voter behaviour and preferences. Therefore, this work presents the
results of behavioural experiments where participants were asked to vote in a
fictional PB setting. We identified approaches to designing PB voting that
minimise cognitive load and enhance the perceived fairness and legitimacy of
the digital process from the citizens' perspective. In our study, participants
preferred voting input formats that are more expressive (like rankings and
distributing points) over simpler formats (like approval voting). Participants
also indicated a desire for the budget to be fairly distributed across city
districts and project categories. Participants found the Method of Equal Shares
voting rule to be fairer than the conventional Greedy voting rule. These
findings offer actionable insights for digital governance, contributing to the
development of fairer and more transparent digital systems and collective
decision-making processes for citizens.
