So whatever you’re gonna do, do it now.
Quinjet Ascent
Hawkeye pulls the Quinjet into a vertical ascent to avoid a pair of Ultron-drones. The background plate for this was just above this traffic circle and parking lot in Gangnam-gu.
At the same intersection above, as the pair of drones launches from the back of the truck to attack the Quinjet, Widow takes her motorcycle down the up-ramp to the lower parking area under the Dongbu Expressway to follow the truck.
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Train Chase
The truck heads through a parking lot under the Dongbu Expressway, keeping pace with a passing commuter train. Captain America is knocked into a train by Ultron, as Widow leaps into the back of the truck. The drones return to take the semi-trailer airborne, with Black Widow still inside.
This entire first half of this truck chase with the train takes place in the parking lot under the expressway between the Samseong-Gyo bridge and the Bong-Eungyo bridge.
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Truck Takes Flight
As the Ultron-bots take off with the cradle, followed by Clint in the Quinjet. The fly above the Han river with the Dongjak Bridge in the background and the Olympic-daero highway on the right.
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Ultron Escapes
Ultron leaves the train and flies off with his companions, grabbing Black Widow in the process. He flies over these train bridges, just west of the Hangang Bridge, as the train speeds on below.
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Train Crash
The train runs off its rails down this street. Background images were taken in and around this area. Note the blue sign in the third image below, compared to the Street View. The final crash of the train occurs in the backlot of Longcross studios, according to Cinefex 142.
Street View
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Train Stops
The train comes to rest on a Korean street. These final couple of shots were filmed at Longcross Studios in England, according to Cinefex 142 and an article about the drone used to shoot this sequence on www.thebroadcastbridge.com.
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(Avengers: Age of Ultron, 2015)