Let a,b be coprime positive integers and let Q be the root lattice of the symmetric group S_a. The action of S_a on the quotient lattice Q/bQ is called the "rational parking space". When b=1 (mod a), the quotient Q/bQ has a beautiful description in terms of the Shi hyperplane arrangement. A mysterious aspect of Q/bQ is that it supports a (conjecturally) symmetric q,t-bigrading, (conjecturally) related to the bigraded Hilbert series of diagonal harmonics. I will explain how to define this bigrading in terms of the root lattice, and how it maps to famous combinatorial versions (bounce, dinv). This comes from my paper (http://arxiv.org/abs/1005.1949) and the recent work of Gorsky-Mazin-Vazirani (http://arxiv.org/abs/1403.0303).