Module 4 · Process Improvement with BPMN and Lean
Value stream mapping
Map a process as a value stream, with process time, waiting time and first-time quality at every step, and calculate the flow efficiency that shows how much of the lead time is real work.
About 25 minutes
The problem
Ask Harbourline's operations director how long clearance takes and he'll say "about eight or nine days". Ask how much of that is work and he'll guess "half, maybe more: customs is slow". Both answers matter, but only one is a guess.
A value stream map (VSM) puts the two side by side for every step: how long the work takes, and how long the item waits before it. When you add them up, the result is almost always a shock. It changes the conversation from "work faster" to "stop waiting".
The concept
What a value stream map shows
A VSM follows one item (a container) from trigger to customer, step by step, and records for each step:
| Data box | Meaning |
|---|---|
| Process time (PT) | hands-on time to do the step once |
| Wait time (WT) | time the item waits before the step starts |
| % complete and accurate (%C&A) | how often the step's output can be used by the next step without correction |
| Who does it | team or organisation |
Underneath, a timeline alternates waits and work, and totals them.
Three numbers that summarise the stream
- Lead time = total time from start to finish (all waits + all process time).
- Total process time = the sum of process times.
- Flow efficiency = total process time ÷ lead time.
In office and service processes, flow efficiency of 5% to 15% is common. Below 5% means the item spends almost its whole life waiting.
Rolled %C&A
Multiply the %C&A of the steps together to see how often an item goes through the whole stream without any correction. Three steps at 90% each give 0.9 × 0.9 × 0.9 = 73% right first time.
Example
Harbourline's clearance value stream, before the pilot (averages per clearance, in hours):
| Step | Team | Wait before | Process time |
|---|---|---|---|
| Check documents | Documentation | 22.1 | 2.0 |
| (if incomplete) request correction and re-check | Documentation, customer | about 72 | 1.5 |
| Submit customs declaration | Customs broker | 18.2 | 1.5 |
| Duty assessment | Customs | 30.5 | 1.0 |
| Confirm duty payment | Finance, customer | 46.1 | 0.5 |
| (Red channel) physical inspection | Customs | 42.1 | 3.0 |
| Release and gate-out | Terminal | 27.2 | 1.5 |
The first step's %C&A is about 66%: only 66% of clearances have complete documents on arrival. Every other clearance takes the correction loop, which on its own adds about three days.
Walkthrough
- For each pre-pilot case, sum the process times of all its activities except delivery.
- Calculate the lead time at port: release − arrival, in hours.
- Calculate flow efficiency: total process hours ÷ total lead time hours, across all pre-pilot cases (the first task below).
- Build the VSM table for the steps, as in the example, using the waiting-time method from lesson 3.
- Mark the three longest waits. They're your improvement targets, whatever the team believes is slow.
Practice
Practice
Before the pilot, what was the average total process time per clearance in hours (all activities except Deliver to customer)? One decimal place.
Practice
Before the pilot, what was the flow efficiency at port: total process hours (excluding delivery) ÷ total hours from arrival to release, across all pre-pilot cases? One decimal place.
Task
6 minSummarise Harbourline's value stream for the operations director in 3 to 5 bullets: the lead time, the process time, the flow efficiency, the biggest waits, and what that means for where to improve.
Your work is checked for
- Three to five bullets
- Gives the lead time
- Gives the flow efficiency
- Names at least two of the longest waits
- Concludes about waiting rather than working faster
- No more than 120 words
Check your understanding
Answer every question to check.