legends · 4 min read ·
Crash Pulse
A crash-test engineer finds a body-shaped load in the empty rear seat of every test since 1988.
**Test Report 7714 — Frontal Offset Deformable Barrier, 64 km/h, 40% overlap.**
**Facility: Halden Safety Test Centre. Vehicle: mid-size saloon, pre-production.**
**Lead engineer: R. Ashby.**
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**1. Setup.** The test vehicle was fitted with two dummies in the front seats, a Hybrid III 50th percentile male in the driver's position, and a female 5th percentile dummy in the front passenger seat. Instrumentation: head, chest and pelvic accelerometers, neck load cells, femur load cells, belt force transducers. Fifty-six data channels in all. High-speed cameras at twelve angles, 1,000 fps.
**2. Test.** The vehicle was propelled along the guide rail and struck the barrier at 64.2 km/h at 11:42 local time. Impact lasted 118 milliseconds. Dummies behaved nominally. Airbags deployed at 14 ms and 16 ms. Belt pretensioners fired.
**3. Results (excerpt).** HIC15 driver: 412. Chest deflection: 31 mm. Left femur load: 3.4 kN. All within regulatory limits.
**4. Anomalies.**
(a) *Channel 41, rear-seat floor accelerometer.* The vehicle's rear footwell was empty, no dummy. The channel shows a trace beginning at 40 ms after impact, consistent with a body in the rear of the vehicle decelerating against the seatback. The trace is shaped like a body. Peak 38 g.
(b) *Camera 9 (rear interior).* The footage shows the rear seat as empty at the instant of impact. At 40 ms, the seat cushion depresses, as under a weight, and recovers.
(c) *Dummy belt channels.* The passenger dummy's shoulder belt transducer shows a secondary spike at 90 ms, indicating a force applied from behind. A hand pulling on the belt.
**5. Recommendation.** Repeat the test.
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**Test Report 7714-R.** Repeat. Same configuration. 64.1 km/h. Rear seat checked prior to the run, confirmed empty, camera 9 covering the footwell.
Anomalies as before. Channel 41 trace identical in shape, peak 38 g, onset 40 ms. Camera 9 shows a depression in the rear seat, at the same instant.
In addition: dummy chest channel shows a small pulse at 60 ms that is not the dummy's. Mass estimate for the unaccounted object, from the deceleration profile: 71 to 75 kg.
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**Test Report 7714-S through 7714-W.** Repeats. A different vehicle each time. Same result. The load on channel 41 is always 38 g. The estimated mass is always the same.
I took the cover off the data-acquisition rack and checked the wiring. I replaced channel 41 with a new accelerometer. I replaced the camera. I put a motion sensor in the rear footwell, a floor mat of pressure switches.
At impact, the switches closed, in the pattern of a seated adult.
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**From: R. Ashby**
**To: S. Pillai (Head of Test Operations)**
**Subject: 7714 series — please read before the programme meeting**
Sunil,
I can't put the above in the formal report. They'd withdraw the test and replace me. But I'd like you to know what I've found, and I'd like you to read this at home, not in the office.
I have gone back through the archive. Our test centre has run 3,214 crash tests since 1988. In 3,208 of them there is a channel 41 trace. Always the rear seat. Always empty. Always the same: onset 40 ms, peak 38 g, 71–75 kg. I never looked because the channel is routinely discarded. It is used by nobody. It was there when we built the rig.
Whoever it is, they've been there every time. Every impact. In every car. For thirty-six years. They get in the back seat of a car that is going to crash, and they're present for the crash, and they're hit. And they never get out. They're always there, at the start of the next test. They wait.
I have worked out what the 38 g is. It is a survivable load. It's a load the human body can take if properly belted. Whoever it is, they are being belted, somewhere in the rig, by the hand that shows up on the passenger-belt trace. They are being looked after. They are being kept intact.
It is not the 3,214 tests that trouble me. It is that I don't think they're suffering. I think they are the reason the cars are safe. I think every car we've ever passed is safe because somebody, in the back, has been taking the worst of it, on our behalf, and has been willing to.
I can't say what they get in return.
I'd like us to stop for a day, Sunil. Just a day. I'd like to put a seat belt in the back seat and leave the car on the rail, and come in on Monday and see if it's been used.
Ray