Product methodology
Fatigue Management keeps three layers separate:
Modelled fatigue exposure + scoped organisational rules + documented management decision
The software does not collapse those layers into a single “safe” or “compliant” label.
1. Modelled fatigue exposure
Section titled “1. Modelled fatigue exposure”The calculation layer uses an RR446-compatible implementation to produce modelled Fatigue Index (FI) and Risk Index (RI) outputs for planned duties.
Relevant inputs can include duty start and end times, shift timing, duty duration, ordered recent duties, break, workload and attention values, and planned one-way travel.
The current roster captures planned duty and travel facts. Break, workload, and attention fields use the documented RR446 defaults; the effective values are retained with the evaluation result.
Duty instants are converted to UK civil time before model inputs are extracted. The calculation layer is kept separate from authentication, databases, HTTP, roster persistence, and policy evaluation.
Read HSE RR446 and the Fatigue Risk Index, FI versus RI, and fatigue model inputs and outputs.
2. Adaptation and data quality
Section titled “2. Adaptation and data quality”The roster application maps planning facts into the model’s expected inputs. Those mappings are kept explicit:
- one known planned journey is used as the available one-way travel value;
- two equal known travel legs use that common value;
- when planned travel is not entered, the implementation uses a 40-minute one-way default inherited from the historic HSE spreadsheet convention — an implementation convention, not an RR446 requirement;
- two unequal known travel legs are left unresolved rather than averaged into an invented FI or RI.
Adaptation notes and effective inputs are retained with the evaluation result.
3. Compatibility verification
Section titled “3. Compatibility verification”The extracted calculation package is checked against a frozen compatibility fixture set containing 47 complete evaluation scenarios and 12 lower-level reference vectors.
These tests demonstrate behavioural compatibility with the extracted implementation for the covered inputs. They are not independent scientific validation of every result, proof of individual risk, or regulator approval.
4. Policy and rule evaluation
Section titled “4. Policy and rule evaluation”Model output is not organisational policy. A separate versioned layer evaluates selected model and roster metrics against an active named profile.
The current optional profile is Rail reference profile 1.0.0. It can produce:
- OK;
- Advisory;
- Managed Level 1;
- Prohibited.
When it triggers, the application can show the reason, measured value, threshold, travel source, and relevant duty context. Managed Level 1 requires an authorised management reason. A Prohibited result under the active profile cannot be overridden within the workflow.
Prohibited is a policy-profile outcome, not a statement that the duty is prohibited by statute.
Rail reference profile 1.0.0 is a product reference profile. It is not an HSE, ORR, RSSB, Network Rail, or regulator-approved standard.
Organisations without an active profile continue to receive modelled FI and RI with a clear “No active policy” state. Rule evaluations are scoped to the active, named policy profile.
5. Decision and record
Section titled “5. Decision and record”The authorised person remains responsible for deciding what action is appropriate. Depending on the outcome, that may include changing the roster, removing an assignment, cancelling future work, or providing a permitted management approval reason.
Fatigue-relevant changes create evaluation snapshots. Current records include calculation inputs, outputs, model and adapter versions, travel provenance, policy identity, triggered reasons, and links to preceding snapshots.
Methodology and model limitations
Section titled “Methodology and model limitations”Model outputs estimate roster-related fatigue exposure; individual fitness remains a separate operational judgement.
In particular, modelled FI and RI:
- are estimates based on population-level research;
- do not directly measure a specific individual’s current alertness, sleep, health, or fitness for duty;
- should not be treated as an automatic safe or unsafe decision;
- cannot account for every operational, environmental, or personal factor;
- do not make FI or RI values universal legal limits.
Fatigue science and organisational policy remain distinct. Applicable rules and competent management judgement remain relevant.
Read limitations of fatigue models before using scores in an operational process.
Compliance positioning
Section titled “Compliance positioning”The product can support consistent checks and records after the applicable rule, policy, contract, or framework is identified. Packaging does not change the limits of the model.
International scope
Section titled “International scope”The underlying fatigue concepts and general roster workflow are not described as UK-only. Regulatory, contractual, and policy conclusions remain jurisdiction- and organisation-specific.