Exam 1 (Lecture 1-8) Key Terms

• Mobility

  ability to move people (or goods) easily from one place to another. (e.g. how far you can go in a given time)
• Level of Service


  A measure of the quality of transportation service. Each mode offers a unique set of service characteristics in terms of travel time, frequency, comfort, reliability, convenience, and safety
• Mode


  a 'kind' of transportation. (e.g. Air, Water, Pipeline, Rail, Roadway, other: pedestrians, conveyor belts, cable systems, etc.)
• Vehicle Miles Traveled (VMT)


  a common unit to measure travel within a region over a period of time
• Derived Demand


  Demand for transportation is a function of personal and business activities, system needs change with priorities and populations.
• E considerations

  Economics, Efficiency, Energy, Environment, Expediency, Equity, Ethics
• Vision


  Important human characteristic of transportation considerations
• Visual Acuity


  Visual Reception: type 1: Visual Acuity: ability to see fine details. Static and Dynamic
• Normal Visual Acuity

  20/20
• PIEV or (PIJR)


  Perception, Identification (Intellection), Emotion (Judgement), Volition (Reaction)
• Perception


  Sees or hears situation
• Identification (Intellection)

  Identify the situation
• Volition (Reaction)


  Acts (time to start events in motion but not actually do action)
• Sight Distance


  length of roadway visible to the driver
• AASHTO

  American Association of State Highway and Transportation Officials
• 2.5 seconds


  AASHTO recommendation for stopping sight distance
• Expectancy


  an inclination based on previous experience to respond in a set manner to a roadway, traffic, or information situation
• FHWA 13-Vehicle Category Classification

  Federal Highway Administration:

  Class 1 - Motorcycles

  Class 2 - Passenger Cars

  Class 3 - Four Tire, Single Unit

  Class 4 - Buses

  Class 5 - Two Axle, Six Tire, Single Unit

  Class 6 - Three Axle, Single Unit

  Class 7 - Four or More Axle, Single Unit

  Class 8 - Four or Fewer Axle, Single Trailer

  Class 9 - Five-Axle tractor semitrailer

  Class 10 - Six or More Axle, Single Trailer

  Class 11 - Five or Fewer Axle, multi-trailer

  Class 12 - Six-Axle, multi-trailer

  Class 13 - Seven or More Axle, multi-trailer
• Classes / Categories often simplified to 4


  Passenger Cars, Buses, Trucks: single and multi-unit, and Recreational Vehicles
• Sight Distance


  the length of the roadway a driver can see ahead at any particular time
• Roadway MOBILITY function

  Provides few opportunities for entry and exit and therefore low travel friction from vehicle access/egress
• Roadway ACCESSIBILITY function

  Provides many opportunities for entry and exit, which creates potentially higher friction from vehicle access/egress
• Locals


  provide mostly land access
• Collectors


  strike a balance between mobility and land access
• Stopping Sight Distance (SSD)


  the distance needed for drivers to see an object on the roadway ahead and bring their vehicles to safe stop before colliding with the object
• Passing Sight Distance (PSD)


  the distance that is required on a highway (generally a two-lane, two-directional one) that will allow a driver to pass another vehicle without colliding with a vehicle in the opposing lane
• Decision Sight Distance (DSD)


  the distance traversed while recognizing an object or hazard, plotting an avoidance course, and making the necessary maneuvers
• Intersection Sight Distance (ISD)


  the distance a motorist can see approaching vehicles before their line of sight is blocked by an obstruction near the intersection
• PIEV (perception-reaction distance)


  The first part of SSD: perception, identification, judgment, and reaction, vehicle traveling at or near design speed
• Braking Distance


  The second part of SSD: once the driver applies the breaks, the vehicle decelerates quickly to come to a full stop
• 2.5 seconds


  AASHTO assumption for SSD
• G


  grade/slope
• Stationing


  fundamental system of measurement used for road layout and construction
• Horizontal Curves


  based on a circular shape, measured length in stationing and direction in bearing
• Vertical Curves


  based on a parabolic shape, represent changes in elevation
• Vertical Alignment


  consists of combinations of straight sections, referred to as tangents or grades, and connecting curves, referred to as vertical curves
• Parabola

  geometric shape of vertical curve
• equal tangents in design


  horizontal distance from center of curve to end of curve identical in both situations
• Crest Vertical Curve

  A vertical curve with the parabolic curve drawn below the two tangents
• Sag Vertical Curve


  A vertical curve with the parabolic curve drawn above the two tangents.