Wade Bartlett

Evaluating the Uncertainty in Various Measurement Tasks Common to Accident Reconstruction

When performing calculations pertaining to the analysis of motor vehicle accidents, this paper describes how investigators must often select appropriate values for a number of parameters. The uncertainty of the final answer is a function of the uncertainty of each parameter involved in the calculation. This paper presents the results of recent tests that were conducted to obtain sample distributions of some common parameters, including measurements made with tapes, measurements made with roller-wheels, skidmark measurements, yawmark measurements, estimation of crush damage from photographs, and drag factors, that can be used to evaluate the uncertainty in an accident reconstruction analysis. The paper also reviews the distributions of some pertinent data reported by other researchers.

Conducting Monte Carlo analysis with spreadsheet programs

Monte Carlo analysis has been shown to be a powerful tool in evaluating confidence limits and probability distributions for values calculated during the analysis of vehicle accidents. The use of this tool has generally required specialized software. This paper presents a method of using the tools provided with most simple spreadsheet programs to conduct Monte Carlo analysis with both evenly distributed and normally distributed variables for cases where the equations can be expressed in closed form. The paper discusses the accuracy one can expect given a particular number of trials and presents example analyses using both even-probability and normal-probability variables.

Evaluating Uncertainty in Accident Reconstruction with Finite Differences

The most effective allocation of accident investigation resources requires knowledge of the overall uncertainty in a set of calculations based on the uncertainty of each variable in real-world accident analyses. Many of the methods currently available are simplistic, mathematically intractable, or highly computation-intensive. This paper will present the Finite Difference method which is a numeric approach to partial differentiation with error analysis that requires no high-level mathematical ability, uses very little computation time, provides adequate results, and can be used with analysis packages of any complexity. The Finite Difference method incorporates an error treatment which provides investigators a basis to qualitatively rank from dominant to trivial the effects of uncertainty and errors in measured and estimated values. This allows for greater efforts to be placed on accident investigation and precise measurements while less effort can be spend on trivial analysis results.

Calculation of heavy truck deceleration based on air pressure rise-time and brake adjustment

It has been shown that one can calculate the braking deceleration capabilities of an air-braked heavy truck given a modest amount of information about the components in the brake system and their adjustment level. The error introduced by ignoring the transient air pressure effects early in the event has been found to be negligible during stops from normal road speeds, but during stops from low speeds, the actual decelerations achieved can be expected to be lower than this overall average value. This paper presents an extension of the Heusser analysis technique to include the air pressure rise-time.

Validation of the Circular Trajectory Assumption in Critical Speed

In a maneuver called a critical speed yaw, which occurs when a driver makes a dramatic steering input, the force required to turn the vehicle in the path requested exceeds the force that the tires are capable of generating. As a result, the vehicle turns in a path primarily defined by available friction and the vehicles velocity. Accident reconstructionists often use the critical speed model to determine vehicle speeds. This model assumes that the vehicles center of mass travels in a circular arc when in a critical speed yaw. This study investigates the validity of this assumption by comparing the results obtained by manually measuring the tire marks, assuming them parallel to the center of mass path, and fitting a polynomial. Findings indicate that the circular arc assumption is reasonably accurate. Results also indicate that 2nd order polynomial is a good approximation to describe the tire mark trajectory. The 3rd order polynomial might provide more accurate estimation for higher speed using the radius of curvature at x=0. Using the radius of curvature at midpoint of the trajectory provides results similar to the conventional method of measuring a chord and middle ordinate and calculating the radius.

PASSENGER VEHICLE BRAKING PERFORMANCE WITH A DISABLED VACUUM POWER BOOSTER

When the vacuum-powered brake booster in a passenger vehicle becomes disabled, the brake force gain of the system is reduced significantly, and the brake pedal force required to lock the tires increases beyond the ability of some adults. In these cases, the maximum braking deceleration achieved by those individuals will be something less than the upper boundary as defined by available traction. This papers goal is: to review the design of vacuum boosters, the literature concerning human ability to depress a brake pedal, and Federal Motor Vehicle Safety Standard (FMVSS) 105 requirements which must be met by vehicle manufacturers; and to present performance data with and without the booster operational for four passenger vehicles. The application of this information to accident investigations involving disabled boosters is discussed. (A) For the covering abstract of the conference see IRRD 899758.