  We propose a one-dimensional model of active particles interpolating between
quorum sensing models used in the study of motility-induced phase separation
(MIPS) and models of congestion of traffic flow on a single-lane highway.
Particles have a target velocity with a density-dependent magnitude and a
direction that flips with a finite rate that is biased toward moving right. Two
key parameters are the bias and the speed relaxation time. MIPS is known to
occur in such models at zero bias and zero relaxation time (overdamped
dynamics), while a fully biased motion with no velocity reversal models traffic
flow on a highway. Using both numerical simulations and continuum equations
derived from the microscopic dynamics, we show that a single phase-separated
state extends from the usual MIPS to congested traffic flow in the phase
diagram defined by the bias and the speed relaxation time. However, in the
fully biased case, inertia is essential to observe phase separation, making
MIPS and congested traffic flow seemingly different phenomena if not
simultaneously considering inertia and tumbling. We characterize the velocity
of the dense phase, which is static for usual MIPS and moves backwards in
traffic congestion. We also find that in presence of bias, the phase diagram
becomes richer, with an additional transition between phase separation and a
microphase separation that is seen above a threshold bias or relaxation rate.
