Network Condition Index (NCI) is a term some agencies and consultants use for a length-weighted roll-up of 0-100 condition scores across all features in an infrastructure network - such as a water distribution or sanitary sewer system - giving you one comparable health score per network. Because longer features carry proportionally more weight, NCI reflects the true condition of the network rather than treating a short stub the same as a major trunk main.
Key points
- NCI rolls up individual 0-100 feature condition scores into one network-level health score
- Each feature is weighted by its length, so big mains and roads dominate the result
- Nodes (manholes, valves, hydrants) typically carry a nominal weight rather than a length
- NCI is calculated per network - a water distribution system and a sewer system each get their own
- Tracking NCI over time supports council reporting and capital planning decisions
Formula
NCI = Σ(condition × length) ÷ Σ(length)
- NCI
- Network Condition Index for the network (0-100)
- condition
- The 0-100 condition score of an individual feature in the network
- length
- The length of the feature - the weighting factor (nodes carry a nominal weight)
Example
Scenario: A water network contains an 800 m trunk main scoring 34 and a 245 m collector scoring 81.
NCI = (34 × 800 + 81 × 245) ÷ (800 + 245) = (27,200 + 19,845) ÷ 1,045 ≈ 45
Result: The length-weighted NCI is about 45, versus a simple average of 57.5. The failing trunk main dominates because it represents most of the pipe in the ground - which is exactly why length-weighting matters for prioritizing capital work.
Why Length-Weighting Matters
A simple average treats a 5 m hydrant lead and a 2 km trunk main as equals. That hides risk: a network full of short healthy stubs and one long failing main can look fine on a simple average while the asset most expensive to replace is quietly falling apart. Length-weighting ties each condition score to how much infrastructure it represents, so the NCI reflects where the money and the risk actually sit. Large failing mains pull the index down, which is the behaviour you want when prioritizing capital renewal.
NCI vs FCI
NCI and Facility Condition Index (FCI) are complementary, not competing. FCI measures buildings and facilities as a ratio of deferred maintenance to replacement value. NCI measures linear networks - pipes, roads, cables - as a length-weighted condition score. A municipality usually reports on both: facility condition for its recreation centres and fire halls, network condition for its watermains and roads.
Tracking Network Condition Over Time
The real value of a network condition figure comes from watching it move. A flat or rising figure shows renewal is keeping pace; a falling one is an early warning that the capital program is not keeping up with deterioration. Whatever roll-up you use, say how many features it rests on: an average built from a handful of inspected segments describes those segments, not the network.
How AssetLab Reports Network Condition
AssetLab reports network condition as a plain average rather than an index. Every feature carries a 0-100 condition score with inspection history, graded Excellent (85+), Good (70-84), Fair (55-69), Poor (40-54) or Critical (below 40). Each network summarizes its replacement value, condition distribution and backlog, and its average condition counts scored features only, with the coverage shown beside it (for example "1 of 2,331 features scored"). Level of Service can set targets on a network for FCI, average condition and % past useful life, and Status keeps a monthly reading for a year-on-year trend.
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Related terms
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