Critical Chain

Buffer Management (3-Zone Traffic Light)

Buffer sizing: Project Buffer = 50% of estimated time to achieve Goal.

Feeding buffers: Each non-constraint Driver has a small feeding buffer protecting the constraint. If a non-constraint Action delays, the feeding buffer absorbs it.

Buffer consumed: 45%  [========----------]
Goal progress:   34%  [======------------]
Status: YELLOW — buffer consumption outpacing progress

Buffer as early warning: Unlike milestone tracking (detects problems after deadline miss), buffer management provides continuous visibility. YELLOW at 20% progress gives weeks of lead time.

Relay Runner Principle

Three rules for Action execution:

1. Start immediately — When approved, execute in the very next chain invocation. No delay. (Prevents Student Syndrome — postponing when there's perceived slack.)
2. Full focus, one at a time — Constraint Driver Actions execute serially. Work one Action to completion before starting the next. (Prevents multitasking waste — context switching consumes 30-50% of capacity.)
3. Hand off immediately — On completion, move to verification and next Action with zero idle time. Early completion is celebrated. (Prevents Parkinson's Law — work expanding to fill time.)

WIP Limits

Late Start Scheduling

Non-constraint Driver Actions start as late as possible (while respecting feeding buffers). This reduces unnecessary WIP and keeps focus on the constraint.

Decision Rules

1. Constraint Actions never wait — always first priority, immediate execution
2. Buffer zone determines response intensity — GREEN: cruise. YELLOW: investigate. RED: escalate.
3. WIP limits are hard limits — do not exceed, even if capacity seems available
4. Relay runner is non-negotiable — no batching of constraint Actions, no multitasking
5. Re-identify constraint after every metric update — the bottleneck can shift
6. Subordination means saying no — non-constraint work that threatens constraint throughput is blocked

Anti-Patterns to Detect