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Related Concept Videos

Elastic Collisions: Introduction01:00

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An elastic collision is one that conserves both internal kinetic energy and momentum. Internal kinetic energy is the sum of the kinetic energies of the objects in a system. Truly elastic collisions can only be achieved with subatomic particles, such as electrons striking nuclei. Macroscopic collisions can be very nearly, but not quite, elastic, as some kinetic energy is always converted into other forms of energy such as heat transfer due to friction and sound. An example of a nearly...
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When two or more objects collide with each other, they can stick together to form one single composite object (after collision). The total mass of the object after the collision is the sum of the masses of the original objects, and it moves with a velocity dictated by the conservation of momentum. Although the system's total momentum remains constant, the kinetic energy decreases, and thus such a collision is an inelastic collision. Most of the collisions between objects in daily life are...
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Impact01:30

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Collisions in Multiple Dimensions: Introduction01:05

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It is far more common for collisions to occur in two dimensions; that is, the initial velocity vectors are neither parallel nor antiparallel to each other. Let's see what complications arise from this. The first idea is that momentum is a vector. Like all vectors, it can be expressed as a sum of perpendicular components (usually, though not always, an x-component and a y-component, and a z-component if necessary). Thus, when the statement of conservation of momentum is written for a...
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Types Of Collisions - I01:04

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When two objects come in direct contact with each other, it is called a collision. During a collision, two or more objects exert forces on each other in a relatively short amount of time. A collision can be categorized as either an elastic or inelastic collision. If two or more objects approach each other, collide and then bounce off, moving away from each other with the same relative speed at which they approached each other, the total kinetic energy of the system is said to be conserved. This...
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Operation of the Collaborative Composite Manufacturing CCM System
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Collision modification functions: incorporating changes over time.

Emanuele Sacchi1, Tarek Sayed1, Karim El-Basyouny2

  • 1The University of British Columbia, Department of Civil Engineering, 2002 - 6250 Applied Science Lane, Vancouver, BC, Canada V6T 1Z4.

Accident; Analysis and Prevention
|April 3, 2014
PubMed
Summary
This summary is machine-generated.

This study introduces collision modification functions (CMFunctions) to better estimate road safety treatment effectiveness over time, moving beyond static collision modification factors (CMFs). CMFunctions provide a more realistic economic evaluation of safety countermeasures by accounting for evolving treatment impacts.

Keywords:
Autoregressive modelsCollision modification factorDistributed lag modelsFull Bayes estimationNovelty effectsObservational before-after study

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Area of Science:

  • Traffic Safety Engineering
  • Statistical Modeling
  • Transportation Economics

Background:

  • Collision modification factors (CMFs) are standard for assessing road safety treatments.
  • Current CMF estimation methods (Empirical Bayes, Comparison Group) provide static point estimates.
  • Static CMFs inadequately capture temporal changes in treatment effectiveness and novelty effects.

Purpose of the Study:

  • To develop and demonstrate collision modification functions (CMFunctions) that incorporate time-varying treatment effectiveness.
  • To overcome the limitations of static CMF point estimates in evaluating safety countermeasures.
  • To provide a more accurate assessment of safety treatment impacts over time.

Main Methods:

  • Utilized a fully Bayesian (FB) framework.
  • Applied linear and non-linear intervention models to estimate CMFunctions with time trends.
  • Case study: 'Signal Head Upgrade Program' in Surrey, British Columbia, Canada.

Main Results:

  • CMFunctions effectively capture the time-dependent nature of safety treatment effectiveness.
  • Estimating CMFunctions significantly impacts the economic evaluation and cost-effectiveness of safety countermeasures.
  • Non-linear models demonstrated a more realistic long-term trend, converging to an everlasting treatment impact.

Conclusions:

  • Collision modification functions offer a superior approach to understanding safety treatment effectiveness over time compared to static CMFs.
  • The temporal dynamics captured by CMFunctions are crucial for accurate economic appraisals of road safety investments.
  • Bayesian intervention models provide a robust methodological framework for developing time-trended CMFunctions.