  Using computer simulation and analytical theory, we study an active analog of
the well-known Tonks gas, where active Brownian particles are confined to a
one-dimensional (1D) channel. By introducing the notion of a kinetic
temperature, we derive an accurate analytical expression for the pressure and
clarify the paradoxical behavior where active Brownian particles confined to 1D
exhibit anomalous clustering but no motility-induced phase transition. More
generally, this work provides a deeper understanding of pressure in active
systems as we uncover a unique link between the kinetic temperature and swim
pressure valid for active Brownian particles in higher dimensions.
