Tree Risk Assessment Calculator

Not exactly -- it borrows ISA TRAQ's likelihood and consequence terminology (Improbable through Imminent; Negligible through Severe) but computes Risk Rating as a direct multiplication of Failure Likelihood and Impact Severity, scaled by Target Value. The official ISA TRAQ process instead runs likelihood of failure and likelihood of impact through one matrix and combines that with consequences through a second matrix. Treat this tool as a planning-level approximation, not a substitute for a credentialed TRAQ assessment.

Risk Rating in this calculator is built only from Failure Likelihood, Impact Severity, and Target Value -- Tree Size plays no part in that calculation. It only affects Liability Score, on the reasoning that a larger tree failing under the same likelihood, target, and impact conditions represents more potential exposure, even though the structural risk rating itself is unchanged.

Target Value applies a multiplier to the base Failure Likelihood x Impact Severity score: 0.5x for Low (open field), 1.0x for Medium (walkway, fence), and 1.5x for High (house, playground), so moving from Low to High triples that multiplier and can meaningfully raise the Risk Rating (1-16) figure. It does not, however, change the separate Category output -- that is determined only from Failure Likelihood and Impact Severity, so Target Value changes how much is at stake in the numeric rating without moving a tree between the Low/Moderate/High/Extreme category bands.

Recommended Inspection Interval is looked up directly from the final Risk Category, not calculated from the individual inputs separately: Low risk suggests re-inspecting roughly every 3 years, Moderate every 12 months, High every 6 months, and Extreme monthly. Risk Category itself comes only from Failure Likelihood x Impact Severity, before Target Value's multiplier is applied, so a tree can move between inspection intervals whenever Failure Likelihood or Impact Severity changes -- Target Value changes the numeric Risk Rating (1-16) and Liability Score but does not move the Category or the inspection interval.