Application of Computer Simulation in Traffic Analysis

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Application of Computer Simulation in Traffic
Analysis

• Presented By Lei Huang

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Motor Vehicle is a Mixed Blessing

• During a average day in U.S., about 100 people
  step into a vehicle and do not emerge alive
• gt90 crashes attributed to driver error rather
  than failures in the vehicle or roadway
• The most important factor in driver error is
  alcohol (40)
• A better understanding of other errors might
  allow people travel at lower risk

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Inappropriate Lane Changing May Have Substantial
Risks

• It causes the individual to straddle traffic
  flows and be exposed to two streams of vehicles
• It requires the driver to make rapid judgments
  about sufficient spacing
• It increases the hazard related to other vehicles
  approaching along the drivers blind spot
• Is disrupts the traffic pattern for following
  vehicles

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Question?

• Whether people can accurately judge if they are
  in a lane that is slower than the other lane on a
  congested roadway?
• Survey indicate most people expect to spend equal
  amounts of time passing and being overtaken
• A videotape obtained from field observations
  confirmed peoples mistaken impressions of speed
  on a congested roadway

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Answer

• Since testing on real drivers seamed to be
  unsafe, unethical and expensive, how do we find
  out the answer to above question?
• Answer Computer Simulation

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Method Individual Vehicle Perspective

• A vehicle would accelerate if it was traveling
  slower than its target speed and no other vehicle
  ahead was within the minimum headway distance
• A vehicle would decelerate if another vehicle was
  ahead and within the minimum headway distance
• A vehicle would maintain a constant speed if it
  achieved target speed and no other vehicle ahead
  was too close

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Method Individual Vehicle Perspective

• The target speed was 63 mi/h (100km/h) for all
  vehicles
• The acceleration and deceleration was set uniform
  for all vehicles
• The minimum headway distance (d) was a function
  of velocity (v), where
• d (v2/100) 1
• thus a vehicle traveling at 100km/h requires a
  minimum headway of 101 m

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Aggregate Traffic Characteristics

• The number of vehicles and amount of available
  roadway was stable, thus conditions which
  provided little total roadway for large numbers
  of vehicles resulted in substantial congestion
• The completely realistic simulation of a single
  lane of traffic was impossible because vehicles
  can differ in target speed, headway tolerance,
  acceleration, deceleration, starting position,
  current velocity.

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Aggregate Traffic Characteristics

• The model was designed with a few initial sources
  of randomness, then gradually made more complex
• The baseline condition assumed that all vehicles
  has identical performance and starting at zero
  velocity
• The starting position (spacing between vehicles)
  was generated by normal distribution

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Aggregate Traffic Characteristics

• The second lane was established with
  characteristics identical to the index lane
• By applying a different starting seed to the
  random generator, the two lanes could follow
  somewhat different patterns yet obtain the same
  average speed

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Psychological and Statistical Issues

• People tend to judge their speed by assessing
  their speed relative to others in the next lane
• Passing epoch
• when the index driver started behind and ended
  ahead of one or more drivers in the other lane
  after a one-second interval
• Being overtaken epoch
• when the index driver started ahead and ended
  behind one or more drivers in the other lane
  after a one-second interval
• Drivers prefer passing rather than being overtaken

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Speed and Position of Vehicle in Single Lane

• Long intervals of slow velocity and short bursts
  of high velocity
• Strong and correlation between a vehicles
  current speed and spacing relative to vehicle
  ahead

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Compare to Vehicle in Next Lane

• Substantial variation in relative speed and
  relative position was observed even over a short
  period of time

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Summary of Finding

• Epochs in which the index car was overtaken were
  more frequent than epochs in which the index care
  was passing(43 vs. 33, ratio 130)
• However, the total number of overtakes equaled
  the total number of passes
• The baseline condition indicated that the next
  line might mistakenly appear faster than the
  drivers current line

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Reasons for the mistaken impression

• A driver on a congested roadway can pass many
  vehicles in a brief interval, whereas it takes
  much more time for the driver to be overtaken by
  the same number of vehicles
• Although every driver should normally expect to
  spend more time going slower than going faster,
  people usually expect that the amount of good
  times should balance the amount of bad times

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Other factors

• Drivers direct more attention ahead than behind
  consequently, passed vehicle turn invisible
  whereas overtake vehicle stay conspicuous
• Glances at the next lane may be more frequent
  when drivers are relatively idle
• Human psychology may make losses appear more
  salient than the corresponding gains

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Less Congested Roadway

• Lesser congestion leads to higher speed, fewer
  passing and overtaking epochs, and smaller
  asymmetry

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Conclusion

• Results from computer simulation suggested a
  roadway illusion namely, that the next lane on
  a congested roadway appears to be moving faster
  than the drivers current lane even if both lanes
  have the same average speed
• Naïve attempts to rush may be misguided without a
  careful understanding of queuing theory