Vehicle profile assumptions affect stopping and handling interpretation. They are adjustable but not a full vehicle simulation.
Assumptions Register
Observed, Derived, Assumed, and Fallback Inputs
Road Risk separates retrieved data, derived calculations, user-selected settings, and fallback assumptions so the model can be inspected.
Assumption Groups
Assumptions and Their Interpretation Role
Surface tags and friction assumptions affect safe speed, slip-style indicators, and braking distance.
Rain, fog, lighting, and visibility assumptions change friction and perception context; they are not live weather measurements.
Fatigue, distraction, BAC, and overspeed are controlled scenario settings, not claims about actual drivers.
Road class, lanes, lighting, pedestrian/cycle context, medians, and barriers depend on public tag completeness.
Fallback values keep the model inspectable when data is missing, but should lower interpretation confidence.
| Assumption | Affects | Input Type | Rationale / Source Context | Adjustable | Limitation |
|---|---|---|---|---|---|
| Vehicle profile | Stopping distance, handling interpretation, visibility/context assumptions. | Assumed / user-selected | Booklet describes 12 vehicle profiles as part of the app model. | Yes | Not a full vehicle simulation. |
| Friction coefficient / surface | Safe speed, slip ratio, braking distance. | Observed if tagged; fallback otherwise | Informed by vehicle-dynamics and road-surface literature. | Yes | Actual tyre-road friction is not measured live. |
| Reaction time | Reaction distance and total stopping distance. | Assumed | Represents perception-reaction delay in the booklet methodology. | Indirectly | Does not observe individual driver response. |
| Rain / wet road | Friction, stopping distance, model multiplier. | Scenario assumption | Weather-risk references support adverse-condition sensitivity. | Yes | Not live rainfall intensity. |
| Fog / visibility | Visibility context and reaction interpretation. | Scenario assumption | Used to test reduced perception distance and interpretive concern. | Yes | Does not measure actual sight obstruction. |
| Lighting | Visibility, infrastructure context, confidence notes. | Observed if OSM `lit` tag exists; fallback otherwise | Added after feedback on infrastructure variables. | Yes / data-dependent | Missing tag does not prove absence of lighting. |
| Fatigue / distraction | Behavioural multiplier and reaction interpretation. | Scenario assumption | Represents reduced driver response capability. | Yes | Not a measurement of real driver state. |
| BAC / alcohol impairment | Behavioural multiplier and stopping-distance interpretation. | Scenario assumption | Included as a controlled risk-factor assumption. | Yes | Does not infer impairment at any location. |
| Overspeed | Centripetal demand and velocity-squared stopping distance. | Scenario assumption | Physics gives speed strong non-linear influence. | Yes | Not evidence of actual speeding. |
| Road classification | Traffic proxy, speed context, baseline exposure assumptions. | Observed OSM highway tag; fallback if unavailable | Used where direct traffic counts are unavailable. | Data-dependent | Road class is an imperfect exposure proxy. |
| Lane count | Infrastructure context and exposure interpretation. | Observed if tagged; fallback otherwise | Booklet logs describe lane-based risk adjustment. | Data-dependent | Missing lane tags are common. |
| Pedestrian / cycle infrastructure | Infrastructure rating and exposure context. | Observed if sidewalk/cycleway tags exist; fallback otherwise | Booklet logs include pedestrian and cycle infrastructure as context. | Data-dependent | OSM mapping completeness varies locally. |
| Median / barrier | Infrastructure modifier and collision-type context. | Observed if available; fallback otherwise | Booklet logs include median and barrier effects. | Data-dependent | Does not replace engineering inspection. |
| Assumption profile | Weather, lighting, fatigue, and multiplier sensitivity band. | User-selected model profile | Poster reports 3 assumption profiles. | Yes | Not a measured confidence interval. |
Judge Focus
Most Important Assumptions to Explain
Friction
Surface Grip Controls Multiple Outputs
Lower friction reduces safe speed and increases braking distance. It is one of the clearest scenario-sensitivity levers.
Reaction Time
Driver Response Shapes Stopping Distance
Reaction time is assumed, not observed, so fatigue and distraction should be used as controlled scenarios.
Road Class
Traffic Proxy, Not Traffic Count
OSM road class helps provide context but is not a measured exposure dataset.
Visibility
Lighting and Fog Change Interpretation
Visibility assumptions can affect reaction context, but they do not prove actual visibility conditions at a road.
Missing Tags
Fallbacks Must Stay Visible
Missing public map tags do not prove a feature is absent; they show where evidence quality is weaker.
Assumption sensitivity
Change one assumption at a time in the live app to isolate its effect on the same selected road.
Data Confidence
How to Interpret Missing Public Data
More coordinate nodes can describe bends more clearly; sparse geometry can make curvature less precise.
Missing surface, lighting, lane, speed, or sidewalk tags do not prove that those features are absent.
Fallbacks keep the calculation running, but they should lower interpretation confidence.
Any operational use would require direct inspection, professional review, and better local data.