  A new class of lattice gas models with trivial interactions but constrained
dynamics are introduced. These are proven to exhibit a dynamical glass
transition: above a critical density, rho_c, ergodicity is broken due to the
appearance of an infinite spanning cluster of jammed particles. The fraction of
jammed particles is discontinuous at the transition, while in the unjammed
phase dynamical correlation lengths and timescales diverge as
exp[C(rho_c-rho)^(-mu)]. Dynamic correlations display two-step relaxation
similar to glass-formers and jamming systems.
