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**Current Trends in Pedestrian Crash Reconstruction - Update**

SATAI July 12, 2008 By: Jerry J. Eubanks Collision Safety Institute Automobile Collision Cause Analysis San Diego, California

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**Current Trends in Pedestrian Crash Reconstruction - Update**

San Diego PD Retired Accident Unit ACTAR Accredited #40 Author Pedestrian Accident Reconstruction and Pedestrian Accident Reconstruction and Litigation Multiple SAE papers Taught at Multiple Colleges 1232 crash tests of which 418 Peds & 122 Bikes

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**Current Trends in Pedestrian Crash Reconstruction - Update**

This lecture is going to talk about different pedestrian equations that use different types of friction. Where the friction is within a constant value i.e.: Where the friction is suggested by the author i.e.: Collins ped friction = 0.8 Searle ped friction = 0.66 Searle recently increased the ped friction = 0.7 ```

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Pedestrian Equations where the author has set the friction within a constant: Those equations are: Appel Barzeley Casteel Davis Dekra Foster & Smith Fugger and Randles Happer Hill ITAI Smith & Evans Sturtz Wood 1991 Wood 1995

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Pedestrian Equations where the author suggests the pedestrians friction : Those equations are: Aronberg & Snider 0.5 Collins 0.8 Hague 0.62 NWUTI – 0.60 Otte Parkka Grass – 0.70 Asphalt – 0.60 Concrete 0.45 – 0.65 Pultar Schmidt & Nagel – 0.7 Stcherbatcheff – 0.71 Wood calculate

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Pedestrian Equations where the author suggests using the vehicle/roadway friction : Those equations are: Aronberg & Snider 0.5 Degger f car * 1.1 = f ped Dekra 1981 Eubanks ** Fall & Slide ** Galli ** Han & Brach Higgins McHenry Rau React & Slide (Vehicle Dist) Rich ** yet if Fwd Proj f = 1.0 Wood 1995 ** Determine the vehicle vs roadway friction and then multiply that value by 1.1 and 1.7 to get a range. For instance if the roadway friction is The pedestrian friction range would be 0.8 – 1.2

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Pedestrian Equations where the author does not use any pedestrian friction value : Those equations are: Clark Vaughan (Pedestrian vs. Vehicle Time and Distance – Pre Impact motion

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Unless otherwise stated most of these equations on a pedestrian, bike or m/c rider. Initially you must know where the AOI is known and the final rest position is. Its simpler to use the authors friction value rather than to defend your deviations in court. There are enough pedestrians equations to allow you to skip one if appropriate. Pultar developed a Fall and Slide style equation whose with his entry in these equation is to use a pedestrian friction value of f = 1.0.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

What if you are working a pedestrian collision with a wrap trajectory that happens on dry asphalt or concrete with a pedestrian collision of – Those equations having appropriate friction within that range can be used. But for instance Otte having a pedestrian friction of should not be used. The friction for the Schmidt & Nagel is between 0.2 – So to use this equation any friction below 0.65 should not be used, but the higher end of 0.65 – 0.7 can be appropriately used.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

During a set of three pedestrian vs vehicle crash tests this year in St Charles Ill. For the first time during each separate crash test, we were able to have the pedestrian slide on a different surface over the asphalt taxiway. For this lecture we will look only at crash test 2. In this crash test the pedestrian slid the whole slide distance on an icy surface.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Video Clips Crash test 2

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**Current Trends in Pedestrian Crash Reconstruction - Update**

For Crash tests 2 a 1987 Honda Accord Lxi 2 Dr Hatchback was used The Engine was an In-Line 4cyl OHC L/ 121 cu. In. Weight 2300 lbs (w/o driver):OAL 175 in The driver weighed 205 lbs: W/B 102 inches: Leading Edge Height 25.5 in.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

CSI Bike and Pedestrian Crash Tests 2 Timer Distance 3.02 ft Timer Time 0.072 sec Vehicle Velocity 41.94 fps Vehicle Speed 28.60 mph Roadway Surface Pedestrian Slid Across Snow Rippled by wind Bike Rider or Pedestrian Trajectory Wrap Initial Ground Contact Rider or Pedestrian 55.83 ft Slide Distance Rider or Pedestrian 32.33 ft Vehicle's Longest Skid Distance 107 ft Calculated Vehicle Skid Friction 0.25

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**Current Trends in Pedestrian Crash Reconstruction**

CSI Bike and Pedestrian Crash Tests 2 Throw Distance Rider or Pedestrian 88.16 ft Vehicle Distance ICP to car front ft Bike Rider or Ped COM Height 35.75 ft Bike Rider or Ped OAH 65 in Throw Distance Bicycle n/a Vehicle Leading Edge Height 25.50 ft Rider % of overall Vehicle Speed 0.71 % Estimated Rider or Ped Take-off Velocity 29.92 fps Estimated Rider or Ped Take-off Speed 20.40 mph If Estimated Take-off Speed Friction 0.43

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**Current Trends in Pedestrian Crash Reconstruction**

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Icy roadway surface over the top of an airport taxiway. For those of you who work or have lived in a snowy/icy area of the country I have a question for you. This ice had looked like waves or bumps on the surface. Does anyone know what has caused this?

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**Current Trends in Pedestrian Crash Reconstruction - Update**

What I would like to work with today is showing how some of the pedestrian equations work with a drastically lowered friction. We will work with the data from crash test 2. There are some equations that allow the investigator to input the pedestrian or vehicle friction factor for each equation.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Lets start with the Searle Equation. The Searle equation actually has three different equations but for this lecture we will just look at the minimum and the maximum equations. Initially Searle believed a friction value of was proper. In the last couple of years Searle wrote a CHP officer that a 0.77 friction would also work.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

The Searle Minimum equation is follows:

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Let’s look at the Collins Equation, which allows the investigator to determine the roadway vs vehicle friction. You could either iterate this equation or use the quadratic equation.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

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**Current Trends in Pedestrian Crash Reconstruction - Update**

The Fall and Slide Variables are as follows, with the lower friction value as: fped = 0.285, fauto = 0.25, h = 2.98 ft, dt = ft fped adjustment value = 1.14 : 1.71

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**Current Trends in Pedestrian Crash Reconstruction - Update**

The Fall and Slide Variables are as follows, with the high friction value as: fped = 0.427, fauto = 0.25, h = 2.98 ft, dt = ft fped adjustment value = 1.14 : 1.71

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**Current Trends in Pedestrian Crash Reconstruction - Update**

The Pultar equation uses the same fall and slide equation but he states that you are to use a pedestrian friction value f = 1.0. Using the f = 1.0 on this case the Pultar equation yields: Velocity = fps and Speed = mph

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Pultar equation is a basic fall and slide equation using f as 1.0. Remember would you want to you any equation that mandates a pedestrian friction of 1.0 when you know the actual pedestrian friction is 0.43 In a case like this, I would suggest you use the physics based Fall and Slide equation. There the investigator will be able to input the actual pedestrian sliding friction in this case the fauto =

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**Current Trends in Pedestrian Crash Reconstruction - Update**

The next set of equations to work are those authors to have put there pedestrian sliding values within a constant. For this quick lecture I have located three of these equations. They authors are as follows as: ITAI and Smith and Evans

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**Current Trends in Pedestrian Crash Reconstruction - Update**

ITAI has had a number of authors provide a series of pedestrian equations that I have been told are based on the SEARLE equation. Basically the ITAI equation is: Using the crash test 2 values the pedestrian departure speed is: Throw distance of ft yields a velocity of fps or a speed of mph ITAI Institute of Traffic Accident Investigators

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Smith and Evans is another of theses Searle based equations Using crash test 2 values the pedestrian t Throw distance of ft yields a velocity of fps or a speed of mph So Smith and Evans yields a speed range between and mph ITAI Institute of Traffic Accident Investigators

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**Current Trends in Pedestrian Crash Reconstruction - Update**

The different equations have speed values as follows: Searle f = 0.66 Min = to Max = mph Collins f = mph Fall and Slide Low f = min = mph Fall and Slide High f =0.427 max = mph Pultar f = 1.0 = mph ITAI (constant) = mph Smith and Evans (constant) min = mph Smith and Evans (constant) max = mph

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**Current Trends in Pedestrian Crash Reconstruction - Update**

As one can see equations that do not allow the investigator to place the appropriate friction appear to assume dry roadway surfaces and will over-estimate the impact speed. Those equations that only have a constant velocity will also over-estimate a low friction roadway. In a pedestrian collision on a dry asphalt or concrete roadway most ped equations can be used appropriately.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

RUN Greg Russell's Pedestrian Excel Program

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Greg Russell’s Spreadsheet Values The actual impact speed for this crash test was mph. Using Greg Russell’s Pedestrian Excel program calculated an average speed 34.2 mph. This is a 20% overestimate the actual impact speed. This uses 28 of the total 36 equations in the program. The +/- 10% Range of the Average Speed coming from Greg Russell’s Excel Program would be between 30.7 – 37.6 mph Why would the program over estimate the impact speed in this situation. Does anyone have an Idea why the program overestimated the impact speed?

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Greg Russell’s Spreadsheet Friction Values Can anyone say what friction value this computer program uses? The program uses the friction values suggested or developed based on the authors suggested values. So in this case the pedestrian sliding friction was on an icy surface during the whole sliding phase of the wrap trajectory.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Greg Russell’s Spreadsheet Friction Values Greg Russell’s Pedestrian Excel program has the ability to exclude some equations when the actual roadway-friction is not within each authors friction value. It maybe appropriate to exclude some pedestrians equations because of inappropriate pedestrian sliding friction values. As you would do it doing the analysis by hand you should be allowed to exclude certain pedestrian equations using a pedestrian equation computer program.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

Greg Russell’s Spreadsheet Friction Values When taking into account for the excluded equations we find the following: The Russell Pedestrian program we only used 12 of the available 36 equation. The program calculated an average speed of mph with a +/- 10% range of 24.8 – 30.3 mph. Remember the actual impact speed was mph.

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**Current Trends in Pedestrian Crash Reconstruction - Update**

CONCLUSION: In a low friction collision i.e. ice, snow or even a wet roadway covered with leaves, the investigator has to be careful to use correct pedestrian equations. That way the investigator won’t be averaging in high friction values that could yield an un- erroneous high vehicle impact speed. Finally, the investigator has the ability to choose proper pedestrian equations using appropriate pedestrian/vehicle friction values when investigating traffic collisions.

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**Current Trends in Pedestrian Crash Reconstruction**

If you use Greg Russell’s Excel program for computing the vehicles speed in a pedestrian collision, you can exclude appropriate pedestrian equations where the friction value is too high. For instance, in this pedestrian collision where the vehicle friction was 0.25, you would appropriately exclude Searle, Collins, Pultar and others whose friction are too high for the collision you are working. Excluding these equation are up to the investigator and not up to the computer program.

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**Current Trends in Pedestrian Crash Reconstruction**

After all the years using this program and over a couple hundred crash tests, Mr. Russell and I take the average impact speed as given by the program calculating a +/- 10% value as being more a accurate speed determination than just say a 30 mph impact. This range yields a speed within about 90% of the crash tests we have run. Most time when it doesn’t work will be within the partial or restricted trajectories.

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