Thoracic Trauma Index (TTI)

Description

The Thoracic Trauma Index (TTI) combines lateral rib and lower-spine accelerations for side-impact assessment. WebSAT supports both ATD tests and cadaver/animal/human test informations, for which age and mass enter the normalized calculation [1] [2] [3].

When this feature is available

TTI becomes available when either the current curve selection or any loaded test contains a thorax measurement set that meets the requirements for the selected impact side. Only channels with a usable data status count.

The required measurement set includes:

• The same occupant or test subject must have all three required acceleration channels with:
  • Axis: Y - LOCAL
  • Units: G'S
• The required attachments are:
  • The upper rib on the selected Impact Side
  • The lower rib on the selected Impact Side
  • SPINE - LOWER

WebSAT checks each occupant or test subject independently and enables TTI if any measurement set contains the complete rib-and-spine channel set for the selected Impact Side.

Settings

Setting	Default	Effect
Cadaver Age (Years)	0	Used for cadaver/animal/human records
Override Cadaver Age from Database?	Off	Uses the entered age instead of the saved test value
Cadaver Mass (kg)	0	Used for cadaver/animal/human records
Override Cadaver Mass from Database?	Off	Uses the entered mass instead of the saved test value
Impact Side	Left	Requires left- or right-side rib channels and applies the correct polarity
Skip Bias Removal	Off	Retains the original baseline during FIR100 processing

Age and mass settings are ignored for ATDs.

How WebSAT processes the data

1. Validate the upper-rib, lower-rib, and lower-spine acceleration channels for the selected Impact Side.
2. Apply the FIR100 impact-test processing sequence to all three channels.
3. Sign-adjust right-side signals so the calculation uses the expected positive impact direction.
4. Find the governing upper- or lower-rib acceleration at each time sample.
5. For an ATD, calculate:

$TTI=\frac{\max(a_{upper\ rib},a_{lower\ rib})+a_{lower\ spine}}{2}$

6. For cadaver, animal, or human data, apply the Eppinger and Kuppa normalization using the selected or database age and mass [2] [3].
7. Find the peak TTI and record the component accelerations at that time.
8. Report TTI, the component peaks, and the applicable reference values.

Reference values and injury risk

WebSAT uses a TTI injury limit of 85 g for four-door vehicles and 90 g for two-door vehicles, pickups, extended cabs, convertibles, and three-door hatchbacks [4].

The lower-spine component is also evaluated with a 3 ms clip when the selected ATD has a populated lower-spine reference value. The Hybrid III and side-impact-dummy values follow the published ATD IARVs and NHTSA side-impact criteria [3] [5]:

ATD	Lower-spine 3 ms IARV (g)
Hybrid III 95th male	54
Hybrid III 50th male	60
Hybrid III 5th female	60
Hybrid III 10-year-old	82
Hybrid III 6-year-old	60
Hybrid III 3-year-old	92
EuroSID	82
WorldSID 50th male	78
SID-IIs 5th female	82
Hybrid III 95th male with THOR-LX legs	73
BioSID 50th male	60

WebSAT reports the TTI limit, the lower-spine IARV, and percent of that IARV when available. TTI is reported as an index in g; this function does not convert the result into a separate AIS probability.

Results

The summary identifies the test, occupant/subject, age, mass, TTI, and the peak upper-rib, lower-rib, and lower-spine accelerations. Use these component peaks to confirm which rib channel governed.

TTI summary table example

This summary table shows the reported TTI result along with the associated test information and component peak values. It helps the user quickly review the governing accelerations, the reported TTI value, and the context needed to compare the result with the applicable reference values.

TTI acceleration channels example

This plot shows the processed upper-rib, lower-rib, and lower-spine acceleration channels used in the TTI calculation. It helps the user verify the selected impact side, compare the relative magnitude of the rib channels, and see which rib response governs the TTI calculation.

References

[1] SAE International. Calculation Guidelines for Impact Testing. SAE Recommended Practice J1727.

[2] Eppinger, R. H., Marcus, J. H., and Morgan, R. M. “Development of Dummy and Injury Index for NHTSA's Thoracic Side Impact Protection Research Program.” SAE Transactions, 1984, pp. 359–387.

[3] Kuppa, S. Injury Criteria for Side Impact Dummies. National Transportation Biomechanics Research Center, National Highway Traffic Safety Administration, 2004.

[4] Trella, T. J. and Samaha, R. R. “Motor Vehicle Safety Standard 214 Side Impact Collision.” In Crashworthiness and Occupant Protection in Transportation Systems. ASME, 1995.

[5] Mertz, H. J., Irwin, A. L., and Prasad, P. “Biomechanical and Scaling Bases for Frontal and Side Impact Injury Assessment Reference Values.” Stapp Car Crash Journal, 47, 2003, pp. 155–188. SAE Technical Paper 2003-22-0009.