Good question! I hadn't realized it until you pointed it out.
Maybe we are to assume he bought a car because Julie moved so far away? They both made a big deal over how far Brooklyn was away from where they lived and how expensive cab rides cost.
If you look really closely as he drives away, you can see the tagline "wheels when you need them" on the bumper. That's what's written on every Zipcar - they're a car sharing company that rents out cars cheaply by the hour. So he didn't have a car - he'd rented one for the hour or so he needed.
shareI noticed that too as he was driving away
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