Crash Data Analysis and ReviewTwo Crash Roundup

Wade Bartlett

Rev. 3

A Two-Crash RoundupWade Bartlett

The plan for this session

• We ran 2 crashes on Monday, with 5 vehicles.

• I will review the basic setup, instrumentation, and vehicles.

• We’ll see a few videos and photos.

• I’m going to go thru a traditional analysis from soup to nuts on Crash 1

• We’ll see the instrumentation and EDR results for Crash 1 for comparison

• I’ll briefly review the data from Crash 2, so you can do whatever analysis you like with it, and know what information is available.

Thanks, guys! • Brian West – Setup Crew & found the cars for us to wrinkle

• Bill Focha – Setup Crew & drove the Schoolbus

• Walt Dobson – Setup Crew & drove the Volvo

• Scott Skinner – Setup Crew & ran instrumentation

• Rick Ruth – Setup Crew & EDR guru

Thanks to the two FHP guys who scaled the bus & Volvo

THANKS!• Osceola County School District – Donated the bus to IPTM

• North Florida Technical College – Donated the Volvo for crashing

• Osceola Auto Salvage – Donated the cars

• Alan Moore – Supplied car scales

• Dan Vomhof – videos, photos, 4N6XPRT Systems vehicle specs

• Glenn Luben – Head Kitten Wrangler

• Jeremy Daily – for supplying Vbox batteries when Racelogic couldn’t

• Russell Strickland – for finding all things I forgot to bring with me

Primary Instrumentation• The big orange Volvo & the bus got a Video Vbox from

Racelogic, running 20Hz data & 30Hz video.

•Video to front &

on the driver.

•GPS antenna on top.

Primary Instrumentation•Data analysis also used for skid-testing.

Instrumentation & Documentation

•Handheld RADAR in line with bullet vehicles

•Crash 1: OEM & “ride along” EDR in target car

•Crash 2: Multiple ride along EDRs in each target car

• Scene scanned by RIEGL

•Aerial video & photos from Forensic Mapping Systems

• I did most of my analysis from Google Earth and tape measures to start with, the way I do most analyses.

Test Setup• Stationary “target” cars all had:• Tires aired up to 36psi• Engine OFF•Key ON• Lights ON•Parking brake set• Service brake applied at least a little

•Bullet vehicles – hard brake shortly after impact

CRASH 1 – THE VEHICLES

CRASH 1 – 1997 Volvo Aero, 6x4• Identified as vehicle “1-1”•17,550 pounds w/ driver• ~ 5,200 pounds per fronts• ~ 1,775 pounds per dual•Airbrakes•ABS disabled

•DDEC3 engine controller -no Data Recording.

(Crash 1, Vehicle 1)

CRASH 1 – 1997 Volvo Aero, 6x4

•Add 225 pounds for extra/different occupants & instruments located about 4 feet (21%) behind front axle

• Splits (0.21*225) = 47 pounds rear and 175 pounds front

• Total: 60% front, 40% rear

• Total weight 17,775 pounds

CRASH 1 – 2004 Pontiac GrandAm

• Identified as Vehicle “1-2” (Crash 1, Vehicle 2)

•4N6XPRT: 3,116 pound curb weight 64/36 split

• Scales: 3,156 pounds, 63.5% front / 36.5% rear

CRASH 1 – 2004 Pontiac GrandAm

•Minispare on L/R

•Airbags intact w/ Event Data Recorder (EDR) from the Original Equipment Manufacturer (OEM)

• “Dry fit”

•Video 1 – The event.

•Video 2 – Crash scene scan fly thru by RIEGL.

Crash 1 – The event.

RIEGL scan – done before the scene was opened

Post Crash aerial photo (courtesy of Forensic Mapping Solutions)

Work the Scene: What’s our Scene Evidence?

Volvo Appr/Dep Angle. Follow the skids, right?

Far as I could tell on scene, Volvo’s path was unchanged. I’m going to call approach and departure angles ZERO

Left = 43 feet 6 inches Right = 43 feet

Volvo Post Impact DistanceRear dual skids measured to center of tandems

Smashed front axle air valve behind the front bumper, causing massive air leak, and loss of front brakes.

Volvo Post Impact DistanceFront skids? Basically there were none.

As it turns out, skids start almost exactly when truck reached the car.

Pontiac – gouges from being driven into pavement

Pontiac – gouges from being driven into pavement

Chassis orientation

Pontiac – gouges from being driven into pavement

Gouge from engine cradle gives location and angle very slightly after impact – I’m calling it AOI.

Pontiac’s AOI

Pontiac Departure Angle…How about this?

Pontiac Departure Angle…How about this?

Don’t fall into the “impact to final rest” trap!

No front skids – front tires were rolling enough to turn the car, so it effectively steered itself to uncontrolled rest

Just don’t.

Gouges have direction early on that gives us a clue

Pontiac Post-impact direction

Gouges have direction early on that gives us a clue

Gouges have direction early on that gives us a clue

Pontiac path – overall path helps, too

Pontiac path – overall path helps, too

Pontiac path – Measure CG distance

Total Pontiac travel ~ 44.5 feet

Before Drones…

•We might have mapped this scene with tape measures in an X-Y coordinate style in days of yore…

Note to Self: Be very careful wearing Bifocals!

Glasses may alter one’s perception of position and depth.

There are more bulbs than the headlights…

Hard to see.

A little back-light,Turn the camera to one sideget focus distance right, and set exposure

Work the Crash – What does it all mean?

• Let’s start by thinking about the pavement drag factor, f

• f on good clean pavement averages 0.76g (SD=0.06g)

• I would expect a sealed parking lot to be about 0.65g

•Commercial truck tires are expected to get about 80% of that (commonly attributed to rubber differences and/or the 100psi they carry), or fCMV= 0.52g. You might have seen 70% or 75% for enforcement purposes, but testing in recent years has shown 80% to be realistic.

Volvo Post Impact drag factor

•Heavy trucks in really good condition can pull 0.55 - 0.6g.

• This truck was not one of those, though it was functional.

• I would at first blush estimate this truck’s stopping ability at 0.45g based on experience, though others in the crash team anticipated closer to 0.4g which would be reasonable, too.

• It actually tested out at 0.46g on this pad.

•We don’t normally get to skid test our customer’s trucks, so…if this were my case…

Volvo Post Impact drag factor

•Depending on where you learned to do commercial truck drag factors, you might do a “Ron Heuser” style brake analysis – which means measure the slack adjuster lengths and strokes, note the drum diameters and shoe friction ranges, look up pushrod forces on tables, etc, and estimate overall brake forces.

•But we see evidence of locked rears, and had no fronts, so there’s no special in-between calculation required…

Volvo Post Impact drag factor

• There was little or no pre-crash braking.

•Using fCMV= 0.52g and multiply it by the weight fraction on the axles still braking after the crash (rear only):

feffective, Volvo =7,147

17,775∗ 0.52g = 0.209g

Volvo Post Impact Speed

S3 = 2 30𝐷𝑓 = 2 30 ∗ 43 𝑓𝑒𝑒𝑡 ∗ 0.209𝑔 = 16.4𝑚𝑝ℎ

Pontiac Post Impact Speed

•Post impact, the Pontiac stopped, so drag factor was greater than zero.

•How much greater? We don’t really know.

•We know it left at something higher than the Volvo -they didn’t pass through each other.

Pontiac Post Impact Speed

• If we assume the front wheels did essentially nothing, and the rears were locked, the effective drag factor is the product of the weight fraction on rear axle and the roadway drag factor:

1,152 𝑝𝑜𝑢𝑛𝑑𝑠

3,156 𝑝𝑜𝑢𝑛𝑑𝑠∗ 0.65g = 0.237g

Pontiac Post Impact Speed

• Leading to a post impact speed of

S4 = 2 30𝐷𝑓 = 2 30 ∗ 44.5 𝑓𝑒𝑒𝑡 ∗ 0.237𝑔 = 17.8𝑚𝑝ℎ

Speed change is inversely related to the mass ratio, which gets us the Volvo’s speed change:

•Without saying it explicitly, this has been an In-Line Conservation of Linear Momentum analysis

• Since the Volvo wasn’t redirected, the 360-degree linear momentum is not appropriate here.

Δ𝑉1 =𝑊2

𝑊1Δ𝑉2 =

3,156

17,77517.8𝑚𝑝ℎ = 3.16𝑚𝑝ℎ

And we go to the Closing Speed equation:

•Where•ΔV2 = Pontiac’s speed change, 17.8 mph•ΔV1 = Volvo’s speed change, 3.1 mph•e = ~10% for wrecks with real wrinkled metal

𝐶𝑙𝑜𝑠𝑖𝑛𝑔𝑆𝑝𝑒𝑒𝑑 = 0.91 17.8 + 3.1 = 19.0𝑚𝑝ℎ

Check internal consistency• I assumed e=10%, but calculating e from our results gets

something different:

• So re-run the numbers with different e until the estimated restitution matches the calculated restitution, and whaa-laah:

S1 = 19.5 mph

S3 = 16.4 mph

S4 = 17.8 mph

e = 7.2%

• DIMS? Does It Make Sense? S3&S4 are a little closer than I would have expected…The front brakes were actually applied a bit, but not much.

𝑒 =𝑆𝑒𝑝𝑎𝑟𝑎𝑡𝑖𝑜𝑛_𝑆𝑝𝑒𝑒𝑑

𝐶𝑙𝑜𝑠𝑖𝑛𝑔_𝑆𝑝𝑒𝑒𝑑=17.8 − 16.4

19.05= 7.4%

Iterative Solutions can be daunting.

• Mr. Attorney: You GUESSED the first value, and then guessed how to change it to get the number you wanted, right?

• My Response, smiling: No, counselor. I selected a seed value to complete the open-loop analysis, and homed in on the actual solution. Not all math problems can be solved in one line, and this is a common and accepted technique in all technical disciplines.

My Final Answer

S1 = 19.5 mph This is the number we’re working to get, right?

S3 = 16.4 mph

S4 = 17.8 mph

e = 7.2%

• DIMS Test:? Does It Make Sense? S3&S4 are a little closer than I would have expected…The front brakes were actually applied a bit, but not much. Bumping up the departure speed to 18.4 actually creates a NEGATIVE restitution, so it can’t be true…This is a good test. I stand pat.

So, let’s go to the tape, Bob:

• VIDEO 3 – In-cab Vbox, 20Hz certified GPS

Departure Angles?

•VIDEO 4 – aerial drone by Forensic Mapping Solutions•Pontiac goes straight back at first – PDOF pretty close

to going right thru CG, BUT when the front tires hook up, it turns. For any COLM – we want the travel direction BEFORE the tires affect the path.

•Another discussion point: Verticality. VID 4a, 300 fps

But wait…•Q: Could we tell from the scene evidence if the car was

moving or not?

•A: I’d say, “No”. The truck being so much bigger (weight ratio of 5.7 to 1), the car’s forward speed could have been low and not changed things.

• If the Pontiac was going backwards, it may have contributed to the post-impact momentum, which we have thus far assumed all came from the Volvo. Doing so will bring the Volvo’s speed down a little.

• So traditional techniques of scene analysis got us 19.54mph, GPS measured 20.9mph

•RADAR got 20…but they truncate.

• I’m good with that.

EDR?• The Original Equipment Manufacturer (OEM) Event Data Recorder

(EDR) in the Pontiac recorded two files: DE and DLE, identical.

• Clearly it has a data-buffering issue, since there was nobody in the car, but the engine spooled way up during the crash.

• GM has only lately updated the DL to mention this, and Rick talked about it.

EDR

• The EDR is slightly off-axis, so understates the speed change slightly. I got 17.8mph it recorded 17.1mph

• If we use it straight up, we reduce the calculated truck speed by 0.7mph

• I’m OK with that, too.

• If you incorporate the slight increase with the cosine of the impact angle, it gets closer to my result.

Other ways to check our speed calculation?

•We could try a crush analysis, but this technique is so fuzzy that it will only tell us if something is GROSSLY off, it won’t help with fine tuning.

• I’m not going to discuss crush analysis today. That’s a whole ‘nuther book.

CRASH 2 – The Vehicles

CRASH 2 – The Vehicles

Aerial Video (courtesy of Forensic Mapping Solutions)

• Video 5 - Ground view

• Video 6 - Aerial view

RIEGL Scans

RIEGL Scans

RIEGL Scans – X-ray

Can you do this with traditional techniques?

• Sure.

•Catalog the scene evidence, final rest, tire marks, etc.

• Find vehicle specifications, including axle weights for the cars

• Estimate the cars’ yaw moment of inertia

•Map the damage patterns and find the PDOF location and direction (pretty much 90 degrees, to the right, eh?)

Can you do this with traditional techniques?

•Use the PDOF’s offset from CG to find the “effective mass ratio”

•Run a rotation analysis – the rear impact faces of the two cars should be leaving this event at about the same speed

•Mass ratio is BIG – on the order of 7 or 8 to one, so even big changes in calculated car speeds won’t change bus result much.

• Let’s see how it went…VIDEO 7

OEM EDR, Only one, in the Buick

• The 1997 Century had the same nondeploy -7.9mph Delta V event 34 key cycles prior as the baseline readout.

• DL’s say it can only be overwritten by a larger Delta V.

• Given the test configuration, it is no surprise the longitudinal component was not over -7.9 mph and hence it did not make a new recording.

RESULT• Impact speed of bus was about 21.9mph.•Departure speed was ~19.2mph•We would expect the contact faces on the cars to leave a

little faster than that (or else the bus passes thru them)• So from GPS, the bus change in speed was just under 3mph•With approximately 7-1 weight ratios, the ends of each car

should be leaving at about 21mph. Yep, sounds right.• The Ford’s secondary slap arrests its rotation, but that’s

about all. Research has shown that for our purposes, secondary slap can be simply lumped in with the first hit in situations like this.

The stuff we’re uploading to the IPTM Server:• This powerpoint

•Photos of the vehicles and instrumentation

•VBOX data files:

*.vbo data files, I’ll try to export them to Excel

*.avi files you’ve seen today with speed readout

• Skid tests:

- Truck sans ABS, with bouncy tandems made 0.45- Bus w/ ABS = 0.7g or so (wow!)- A rental Prius w/ ABS made 0.85g

The stuff we’re uploading to the IPTM Server:

•RIEGL scans – LAS files & PNGs I’ve shown today

• Forensic Mapping Solutions aerial video of both crashes and whatever else I get

•Autostats printouts from 4N6XPRT (Dr Dan and DV3 Vomhof)

•Video of RADAR guns on both bullet vehicles

•CDR PDF files from the OEM EDRs and Rick Ruth’s ride-along EDRs

IPTM Crash Test DebriefRide-along EDR’s

Why install ride alongs?

• We crash older less expensive cars to keep conference costs reasonable

• The 1995 Taurus did not have any factory EDR. The 1997 Buick Century had an X delta V only EDR but was being used in a mostly Y Delta V crash.

• Adding a ride along is an inexpensive way to gather more data

Crash 2

• Ride along in trunk at forward edge of spare tire well

• Measured mostly side Delta V but had an X component as vehicle began to rotate

• Factory EDR did not overwrite older -7.9X event

• Front ride alongs did not reach 5mph threshold or had electrical power loss issues

Bus

Century

Crash 2

• Ride along in trunk at forward edge of spare tire well

• Measured mostly side Delta V but had an X component as vehicle began to rotate

• Factory EDR did not overwrite older -7.9X event

• Front ride alongs did not reach 5mph threshold or had electrical power loss issues

Bus

Taurus

The end.