An unsurveyed road is unknown, not zero
A network summary is only as honest as the way it treats the roads nobody has looked at. Here is how gaps quietly distort council road reporting, and a five-point check for your own figures.
Two quiet ways to get it wrong
Every council road network has gaps in its condition data: a new subdivision not yet surveyed, a rural link the survey vehicle skipped, a section whose last rating is six years old. What happens to those gaps decides whether anyone should trust the rest of the numbers.
There are two common mistakes, and they push the answer in opposite directions.
Scoring the gap as zero. A spreadsheet treats a blank condition cell as 0. The network suddenly looks worse than it is, and the “worst” roads on the list are simply the ones nobody measured.
Averaging the gap away. The unsurveyed roads are dropped from the calculation, but the result is still presented as “the network”. The network now looks better than anyone knows it to be, and the gap disappears from view.
An illustrative example (made-up numbers): a council has 500 km of sealed road. 450 km were surveyed and average 70 out of 100. 50 km were not surveyed.
| How the gap is treated | Reported network condition | What it hides |
|---|---|---|
| Scored as zero | 63 | Makes 50 km of unmeasured road look failed |
| Averaged away | 70 for “the network” | Hides that 10% of the network is unknown |
| Reported as unknown | 70 across the 450 km surveyed; 50 km (10%) unknown | Nothing |
Only the last line is a statement an auditor, a councillor or a funding body can rely on.
Why it matters more than it looks
Condition figures feed budgets, works programmes, asset valuations and grant applications. A gap that is hidden in one of them is hidden in all of them.
This is a known weakness in practice, not a local quirk. The US Federal Highway Administration's 2022 Pavement Management Roadmap, built from a survey of every US state transport agency, lists “assessing and addressing missing data in the PMS decision-making process” among the gaps practitioners want closed. In Australia, ALGA's 2024 National State of the Assets report notes that councils expressed more confidence in their condition data than in their function and capacity data, a reminder that confidence varies by data type and should be stated, not assumed.
A five-point check for your own figures
- State coverage beside every average. “70 across 450 km surveyed (90% of the network)”, not “network condition 70”.
- Separate “never surveyed” from “surveyed long ago”. A 2019 rating is evidence of something; a blank is evidence of nothing. Show the survey date per section.
- Never let a blank become a number. Check every formula and import that turns empty cells into zeros.
- Carry the unknowns into the works programme. List them as “needs inspection” rather than letting them silently fall off or rise to the top.
- Report the unknown length in budget papers. It is part of the risk a council is carrying, and councillors are entitled to see it.
How PaveKeep handles this
PaveKeep was built on this rule. A road nobody has surveyed is excluded from condition figures and reported as unknown: it is never scored as zero and never quietly averaged away. Every figure PaveKeep produces can be traced back to the survey, the setting and the arithmetic behind it, so a reader can see exactly which roads a number covers.
PaveKeep is built for small and regional councils and is not yet in use at any council. If you would like to see how it treats gaps on a full working example, ask for a walkthrough.
Sources
- Federal Highway Administration (2022), Pavement Management Roadmap, FHWA-HIF-22-054, gap assessment, Topic Area 4-4.
- Australian Local Government Association (2024), *National State of the Assets Report 2024*, p. 3.