Recently, ACTAR (Accreditation Commission For Traffic Accident Reconstruction) submitted a request to the U. S. Department of Labor requesting an occupational code or definition for Traffic Collision Reconstructionist.
The definition submitted by ACTAR defines a Traffic Collision Reconstructionist as follows - "Inspects and evaluates motor vehicle traffic collision scenes including collecting, photographing, measuring, recording and evaluating physical evidence from the road, environment and vehicles to determine how the collision occurred.  Evaluates physical injury to vehicle occupants and pedestrians in relation to determining subject motion during the collision process.  Confers with operators, pedestrians and witnesses or reviews statements from these persons obtained by others.  Analyzes motions of vehicles, occupants, pedestrians and utilizes equations to determine time, distance, velocity and/or speed of collision involved vehicles.  Evaluates data to prepare verbal or written reports.  Interprets applicable laws and regulations to advise employer on legal requirements.  Applies scientific principles to formulate opinions relative to collisions which are otherwise unknown or are a matter of dispute.  May testify in legal proceedings."
The definition is intended to be all inclusive of the numerous attributes routinely used by a collision reconstructionist.

What tires are involved?
The only tires involved in this recall are Firestone ATX and ATX lls of the P235/75R15 size, and Firestone Wilderness AT tires of the same size that were produced in Firestone's Decatur, Illinois plant.  To determine if your Wilderness ATs were made in Decatur, find the U.S. DOT Safety Standard Code. (Simply look under your vehicle with a flashlight.  There is no need to lift or raise the vehicle.)  If the code reads DOT VDHL, your tires should be replaced.  Tires of any other size or with any other DOT code are not part of this recall.  The DOT code is located on the inboard sidewall.  Inspect tire DOT code with the vehicle on the ground.  For additional up- to-date information, log on to www.ford.com.

What vehicles are involved?

!  '91 - '00 Ford Explorers !  '91 - '00 Ford Rangers  !  '91 - '94 Ford F-Series
!  '94 - '00 Mazda B-Series !    '91 - '94 Mazda Navajos  !  '96 - '00 Mercury Mountaineers
! '91 - '94 Ford Broncos !  '01 Ford Explorer Sport Tracs

Any time someone provides you with a speed estimate based on skid marks alone, strongly suspect the estimate is low.

The Skid Mark Calculation

The math behind the skid mark calculation is not complex. You need a calculator with a square root key.  The basic formula is S = /30DF

S = Speed
30 = Constant for Gravity
D  = Distance of Mark
F = Friction

The only two variables are distance and friction. While this is not complicated, a lot of mistakes are made here.

Distance - It should be simple to measure the length of a skid mark. Why are so many mistakes made? If you remember that most vehicles have four wheels, then there should always be four marks. Right? Not necessarily. If there are less than four marks, then you need to determine why.  The reason could be related to brake failure, weight shift or roadway characteristics. To be conservative, add the length of each mark and divide by the number of  marks.

Example: Mark 1  28 feet
  Mark 2  32 feet
  Mark 3  26 feet
  Mark 4  42 feet

The total of 128 feet divided by 4 equals a 32 foot average.  This is the number to use in the distance variable.

Friction - Friction is a function of the interface between the tire and the road.  Below is an illustration of a friction chart.  In the absence of a reliable friction number, .65 will provide a conservative estimate on dry roads.

So, if a vehicle skids an average distance with all brakes locked for a distance of 178 feet, on a blacktop country road, the formula would look like this:
S = /30DF
S = /30*178*.65
S = /3471
S = 58.9 MPH

Some of this has been rather simply stated.  Those of you who have been through one of my courses know other things such as grade and braking efficiency, can affect the final answer.  However, if you follow these steps, you will come very close to the right answer.

Accident Technology & Engineering, Inc.
11923 Centre Street, Suite B
Chester, VA  23831

Reprinted from ....NHTSA...      Auto Safety Hotline (888) 327-4236      Office of Defects Investigation

Manufacturer:  Isuzu Motor, Limited    1998 Isuzu, Rodeo
Vehicle Description:  Sport utility vehicles.  Paint was applied unevenly on the rear axles, resulting in insufficient paint hardness.  Should this occur on the surface that contacts the rear axle lower link bracket bolt head and/or nut, the nut may loosen.  The bolt could detach fully, causing separation of the lower link from the rear axle, increasing the risk of loss of vehicle control.

Manufacturer:  Toyota Motor Co., Ltd.    1998 Toyota Camry
Vehicle Description:  Passenger vehicles. The steering wheel set nut may not have been sufficiently tightened causing steering vibration and looseness. This can result in a loss of vehicle control.

Manufacturer:  Chrysler Corporation    1996 Chrysler LHS
Vehicle Description:  Passenger vehicles built with 3.5L engines.  The fuel injection delivery system can leak fuel from some of the sealing O-rings or from hair line cracks in the thermoset fuel injection rail.  Fuel leakage in the presence of an ignition source can result in a fire.

Manufacturer:  Subaru of America, Inc.    1998 Subaru Legacy
Vehicle Description:  Passenger vehicles equipped with automatic transmissions.  Due to poor welds, ignition keys can stick, shift levers/linkages can break and shift levers can move.  This condition can cause unexpected movement of the vehicle increasing the risk of a crash or property damage.