In this episode Abraham refers to Glenn as 'Casey Jones' with his determination to get to Maggie by following the train tracks. This is a reference to the real-life Casey Jones, who was an American Railroader for the Illinois Central Railroad from the years 1863 - 1900. Casey Jones passed away while on a train that collided with a stalled freight train in Mississippi.
One of the zombies in the tunnel has more than a passing resemblance to "Bub" from George A. Romero's Day of the Dead (2008).
Abraham, played by Michael Cudlitz, says, "Tired is slow; slow is dead." This is stylistically and structurally similar to a axiom used in the Special Ops community to caution that haste leads to mistakes, missed targets, and inefficiency. It's often quoted in Close Quarters Battles (CQB) training situations such as room clearing where each soldier is responsible for clearing his sector of fire. The sage truism is concisely delivered as as, "slow is smooth; smooth is fast."