Reducing Lead Time: A Practical Lean Approach
Lead time gets measured by the clock on the wall, not the time a team is actively working. A permit application that takes twenty minutes of actual processing might take six weeks from submission to approval. The difference — five weeks and six days of waiting — is the problem Lean is designed to solve.
The Lead Time Formula
Lead time can be expressed simply: Lead Time = Process Time + Queue Time. Process time is the work actually being done on an item. Queue time is everything else — waiting for a decision, waiting for a resource, waiting in a batch to be processed, waiting for approval from someone who is in a meeting. In most service and administrative processes, queue time accounts for 70 to 95 per cent of total lead time. This means that working faster — doing the actual work more efficiently — has a far smaller impact than reducing waiting.
Why Lead Time Matters
Reducing lead time creates value across three dimensions:
Customer satisfaction: faster delivery is, all else equal, a better customer experience.
Work-in-progress reduction: lower lead time means fewer items are open and partially complete at any given time, which reduces coordination costs and error rates.
Cash flow: in project environments, shorter lead time means faster invoicing and faster collection.
Lean Tools for Lead Time Reduction
Lean offers several complementary tools for attacking lead time, each addressing a different root cause of queue accumulation:
Pull systems: instead of pushing work into the next stage as soon as it is ready, pull systems only release work when the downstream stage has capacity. This prevents the queues that build up when upstream stages produce faster than downstream stages can consume.
Batch size reduction: large batches accumulate before being processed, creating inherent queue time. Reducing batch size — processing one item at a time, or smaller groups — reduces average waiting time dramatically, even if the process rate stays the same.
SMED (Single-Minute Exchange of Die): originally developed for manufacturing changeovers, SMED's principle applies anywhere there is setup time between work items. Reducing setup time makes it economical to process smaller batches, reinforcing the batch-size reduction benefit.
WIP limits: capping the number of items allowed in each stage of a process forces the system to finish work before starting new work. This is the core mechanism of Kanban and is one of the most effective tools for surfacing and eliminating bottlenecks.
A Worked Example: Permit Processing
Consider a municipal permit processing office. Applications are submitted, reviewed for completeness, assessed by a technical officer, approved by a manager, and issued. Total process time across all steps: approximately forty-five minutes per application. Actual lead time: three to four weeks. A value stream map reveals the cause: applications are batched weekly for technical review, the technical officer handles them in a single session, and managerial approval waits for the next weekly sign-off meeting.
Three interventions reduce lead time to four days without adding staff. First, applications are reviewed for completeness daily rather than weekly, eliminating the first major queue. Second, technical officers process applications as they arrive rather than in a weekly batch, applying a WIP limit of three concurrent applications. Third, managerial sign-off moves to a daily fifteen-minute review rather than a weekly meeting. The work itself has not changed; only the flow of work through the system has changed. That is the essence of Lean lead time reduction.
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