Lecture 2 - Traffic Flow Fundamentals Flashcards
involves the development of mathematical relationships among the primary elements of a traffic stream: flow, density and speed
Traffic flow theory
These relationships help the traffic engineer in ____, _____, and ______ the effectiveness of implementing traffic engineering measures on a highway system
planning, designing and evaluating
is used in design to determine adequate lane lengths for storing left-turn vehicles on separate left-turn lanes, the average delay at intersections and freeway ramp merging areas, and changes in the level of freeway performance.
Traffic flow theory
simulation where mathematical algorithms are used to study the complex interrelationships that exist among the elements of a traffic stream or network and to estimate the effect of changes in traffic flow on factors such as crashes, travel time, air pollution, and gasoline consumption.
Traffic flow theory
a graph that describes the relationship between the location of vehicles in a traffic stream and the time as the vehicle progress along the highway
Time space diagram
flow occurring at long sections of road where vehicles are not required to stop by any cause external to the traffic stream
Uninterrupted Flow
flow occurring at intersections or driveways where vehicles are required to stop by any cause outside the traffic stream β such as traffic signs (STOP or YIELD), traffic signal lights, etc.
Interrupted flow
equivalent hourly rate at which vehicles pass a point on a highway during a time period less than 1 hour
Flow
equivalent hourly rate at which vehicles pass a point on a highway during a time period less than 1 hour
Density or Concentration
is the rate of motion; distance travelled by a vehicle during a unit of time
Speed
the average of all vehicular speed at any given time
Mean speed
is the arithmetic mean of the speeds of vehicles passing a point on a highway during an interval of time
Time mean speed
is the harmonic mean of the speeds of vehicles passing a point on a highway during an interval of time
Space mean speed
is defined as the time interval between passage of consecutive vehicles at a specified point on the road with a unit of time per vehicle
Time headway
is the distance between two vehicles measured from the front bumper of a vehicle to that of another
Spacing / Space headway
The fundamental traffic equation relating flow, density, and space mean speed is given as:
πΉπππ€ = ππππ ππ‘π¦ Γ π ππππ ππππ π ππππ
Or,
π = π’sπ
When the density on the highway is 0, the flow is ______ because there are no vehicles on the highway
zero
. As the density increases, the flow____
also increases
When the density reaches its maximum the flow must be 0, because vehicles will tend to line up ________
end to end
As the number of vehicles in a road section increases, there is a _______ in speed, in particular, a continuous increase in flow will result in a continuous decrease in speed.
linear decrease
space mean speed at zero density
Free flow speed
density at zero space mean speed
Jam density
he hypothesized that a linear relationship existed between speed and density, which he expressed as follows:
Greenshieldβs model
