A. In the series finale, Episode 10, of Season 9, "Sins of the Fathers“.
At the end, Angela tells Harrison to get out of town and never come back.
She tells him to drive through town, and just past the truck stop, he’ll find the entrance to I-86 W.
He does just that.
And after driving past
several familiar spots in iron Lake, we see him heading out of town on
I-86, as a line of police cars speed past him in the opposite direction,
heading to Iron Lake and the crime scenes he left behind.
As he drives, we hear Dexter’s voice reading the letter he had sent to Hannah about why he had to leave them.
The very final scene sees him driving away from Iron Lake on "I-86 W".
But of course, since this season was filmed in Massachusetts, this isn’t really I-86 W.
In real life, this is MA-140, in Gardner, Massachusetts.
When we see Harrison drive under an overpass, that is the Kelton Street overpass, and he is headed west on MA-140.
Here is a matching StreetView:
The
scene where we see a caravan of police cars speed by, their lights
flashing, on their way to Iron Lake, was shot just south of the exact same spot on the highway that we saw back in Episode 2, where Dexter dropped Matt’s glove in the woods next to the highway.
Approximate GPS coordinates: 42.601605, -71.973046
Here is a matching StreetView:
Harrison is driving west/northwest while the cop cars are speeding east/southeast.
Most likely, they filmed both scenes (the glove scene and this driving-out-of-town scene) around the same time.
Q. How the heck did you figure out where it was?
A.
There is a shot during the sequence, just after the police cars pass by,
when the camera tracking Harrison‘s car rotates upside-down.
I flipped that screenshot back right-side-up in PhotoShop, and one thing I immediately noticed was the same blue water tower
in Gardner which helped me identify the spot back in Episode 2.
So I knew I which street they were on. Traffic signs and unique
trees allowed me to pinpoint the exact spots on that street.