Chebotarev geodesic theorem: split case

We study the prime geodesic theorem in congruence classes of ${\mathrm{S}\mathrm{L}}_2(\mathbb{Z})$. We generalize previous work of Luo and Sarnak and of Soundararajan and Young, and prove that the geodesic analogue of the Chebotarev density theorem holds with exponent $25\mathrm{/}36+\epsilon$. In particular, we deduce that the prime geodesic theorem holds with exponent $25\mathrm{/}36+\epsilon$ for any congruence subgroup of ${\mathrm{S}\mathrm{L}}_2(\mathbb{Z})$.