Feels too easy, as the policeman cannot "follow" the thief, but change lanes randomly. And even more easy, when I noticed that player can run all the time. I am used to harder games.
Please try Texas Instruments TI-99/4A´s "Car Wars" on example, it´s a nice game.
But I like your game and I did notice that difficulty level gets better suited for me when there´s more policemen chasing (or running aimlessly around;)) the thief. Thank you!