Datum point and reference marks
The vehicle datum point and the VSB datum line are fixed marks. The penetration and debris distances are measured from them.
Basis. Annex A is normative; the public guidance explains the measurement. The clause number and defined terms are the standard's; the explanation is our own.
Annex A is normative. It is the measurement sheet for the test vehicle. The control ids on this site are our record codes; the citation names the annex and the clauses that supply the facts.
What annex A-04 asks
This control covers the datum and the marks that anchor every distance. On the vehicle, the datum is a fixed mark used for measurements before and after the hit. On a car or a 4x4 crew cab pick-up it runs through the middle of the A-pillars, at the windscreen's lowest point. On an N1, N2 or N3 vehicle it crosses the front edge of the lower load bed and the chassis rail. On the ground, the barrier datum is a line marked before the test, set vertically under the most forward part of the structure that resists the hit. It is neither the front of the foundation nor the rear face. Clause 6.4.5 places the marks that let the distances be read.
Why it matters
The datum is the anchor for every number in the report. If the vehicle datum point is in the wrong place, the penetration is wrong. If the VSB datum line is drawn at the foundation edge, the penetration is measured from the wrong face. If the markers are not visible in the photographs, no one can check the measurement after the event. These are small setup decisions with large consequences, and they are the first thing a careful reviewer checks.
What good looks like
Put the datum definitions on the test drawing and on the site drawing. Photograph the marks before the impact and after it. Record the height of the initial contact point relative to the datum. Ask the report to state which datum was used and where it was. Do not accept a penetration figure without the datum record.
Evidence an assessor asks for
The reviewer will ask where the measurement started. A penetration figure with no datum is a number without a meaning.
- Datum drawing The vehicle datum point and the VSB datum line, drawn on the vehicle and the site
- Mark survey The position of the marks before impact, with a photograph and a measurement
- Contact height The height of the initial contact point relative to the datum
- Post-impact marks The marks after impact, showing whether they moved
- Measurement note The datum used for each reported distance
Where it commonly fails
- The datum line is drawn at the foundation edge or the rear face
- The vehicle datum point is assumed to be the bumper for every body type
- The marks are not visible in the photographs
- The marks move during the impact and no one records the movement
What to do before the amendment publishes
Add the datum drawing and the mark survey to the test brief. Require the report to name the datum for every distance.
Read across
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