Why is the center row tapped repeatedly in Car Sort Level 273?

Each pass exposes another required color, culminating in the long pink layer used by the lower receiver.

What is the critical capacity checkpoint?

At 10/12, wait for cyan or pink to enter before opening another lower queue.

Car Sort level guide

expert 8 colors

Car Sort Level 273 cycles a mixed center row into a long pink queue while four lower boxes compete for a 12-space double-deck road.

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Tap the two outer upper boxes, then establish the cyan and red upper receivers.
Clear the center horizontal row from left to right, waiting for each visible pair to enter.
Tap lower-left purple/red, then lower-right white/yellow and pause at 10/12.
Return to upper cyan, upper red, and the center row after road space reopens.
Work through the two inner lower boxes to reveal pink, purple, blue, and yellow.
Tap the center row again when its long pink layer appears.
Finish upper purple and red, then lower blue, pink, yellow, and white.
Let the final pink traffic drain the road to 0/12.

Colors in this level:

Cyan, Red, Purple, Pink, Yellow, White, Blue, Burgundy

Releasing two unmatched lower colors together when occupancy is already 10/12.
Treating the center row as permanent overflow instead of a changing source queue.

Board notes 5 details

Layout: Four upper boxes flank one center horizontal queue, with four lower boxes beneath the second loop and a 12-space occupancy counter.
Goal: Establish cyan and red upstairs, then revisit the center row until its pink layer can enter the lower receivers.
Opening: Tap the two outer upper boxes, then the cyan and red upper boxes before clearing the center row left to right.
Danger Zone: Releasing another lower pink or purple pair at 10/12 blocks the center cyan cars needed for the next reveal.
Mechanics: A multi-layer center row repeatedly changes color while four lower question queues use the same narrow road.

Why is the center row tapped repeatedly in Car Sort Level 273?
Each pass exposes another required color, culminating in the long pink layer used by the lower receiver.
What is the critical capacity checkpoint?
At 10/12, wait for cyan or pink to enter before opening another lower queue.