The side quest

Finding all 7 taxis finishes the side quest The Last Taxi, which is one of three requirements for the Threshold Researcher trophy/achievement (alongside Unsupervised Science and Crossing the Threshold). The quest starts when you inspect any taxi; the only requirement is reaching a taxi's area.

The premise: Dylan hears honking from a taxi — maybe someone is in trouble. Objectives: (1) Help the Taxi Driver, (2) Get Back to Manhattan, (3) Get the Caller Back to Manhattan.

How the taxis work

Taxis get marked on the map when you get near them. There's one per region, and they can be done in any order. For every taxi: find it, interact with it, and it takes you to a separate area — a Threshold — where you must complete the puzzle inside to be released. Inside each threshold, first answer the ringing phone in the alley, then identify the correct taxi across 3 cycles. The right vehicle is always the one that differs from the others (light on/off behavior, blinking patterns, shadows, and so on).

Taxi locations and puzzle solutions

  1. Downtown — north of the deserted road checkpoint on the main road. Inspect it with L1/LB, then inspect the right passenger door and choose to get in. It transports you to a new area; answer the phone there. To leave this threshold: take the cab with the TAXI roof light switched on. In the second cycle, take the taxi whose roof light stays lit as you approach. In the third cycle, take the taxi whose top light is currently lit — it blinks on and off, so move fast to spot the lit-sign cab.
  1. Central — north of the deserted road checkpoint on the main road. First cycle: enter the taxi with its roof light on. Second cycle: enter the one with headlight, taillight, and top light all on. Then repeat both steps — roof-light-only taxi, then headlight/taillight/top-light taxi — to exit the Threshold.
  1. Evacuation Zone — in the center of the area west of the Evac Building, in the alley between the three streets near the laser group. Answer the phone in the alley. First cycle: enter the taxi whose lights flash opposite all the others. Second cycle: the taxi that flashes twice in a row while the rest flash once. Third cycle: the taxi that doesn't flash along with the others.
  1. West Incursion Zone — southwest of the Empire Avenue fast travel door, in the area's "upside down" section, stuck to a wall. Answer the phone in the alley. First cycle: enter the taxi under the flashing streetlight. Second cycle: the taxi under the non-flashing streetlight. Third cycle: the taxi whose streetlight flashes opposite all the others.
  1. The Park — southwest of the Mold Factory fast travel point, at the top of the parking garage. From the northwest street corner just outside the garage, climb the big blue mold to the roof where the vendor truck is, then drop down one floor to the taxi. Answer the phone in the alley. First cycle: destroy the Mold to find the trunk and hood, then fit them onto the taxi. Second cycle: pick up the hood and two wheels and reattach them — take the yellow hood farther down the road, not the blue one near the tires. Third cycle: destroy the Mold to reveal the car, then attach the correct parts — fender, hood, and top light are behind/left of the car; trunk and rear bumper are off to the right.
  1. Underpass — in the far southeast of the area, reached during the story after riding the cable car; in the northeast corner of the large Mold-filled room. Answer the phone in the alley. First cycle: enter the taxi whose lights do NOT turn off with the rest of the lights. Second cycle: the taxi whose headlights and taillights turn off when the lights flicker. Third cycle: the taxi with no lights on while the streetlights are on.
  1. The Unknown — on the Evac Building island, north of the building. Answer the phone in the alley. First cycle: pick up the light and shine it at the cars to project their shadows on the wall; enter the one whose shadow matches a taxi rather than a different vehicle (the correct vehicle appears random, so check the shadows rather than relying on a fixed position). Second and third cycles: repeat the same shadow check.

Final step — Get the Caller Back to Manhattan

After all 7 taxis are done, you land on a street once more; go into the alley and answer the phone one final time to complete the side quest. The reward is the Untapped Coffee Cup Artifact.

Tips

Watch for what makes the correct taxi different each cycle — the puzzle logic is always "spot the odd one out," so study the taxis before interacting. The Underpass taxi needs story progress (the cable car ride), and the Unknown taxi needs Pope's Research travel, so don't be surprised if those come last. For the complete quest rundown, see The Last Taxi, and for the other Threshold pieces, Testing Facilities.