03 同济大学道路工程——涂辉招Traffic Engineering.ppt

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Traffic flow theory
• • • • • Macro & Micro variables (宏观/微观变量) Vehicle trajectories （车辆行驶轨迹） 车辆行驶轨迹） Time/distance headways （车头时距/间距） 间距） Time/local mean speeds （地点车速） 地点车速） Space/instantaneous mean speeds （空间车速） 空间车速）
n q= = T
1 = = n ∑ i =1 hi 1 ∑ in=1 hi h n
n
1
• Referred to as flow, volume (US) • How can flow be measured?
Road Engineering
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Macroscopic flow variables (2)
Road Engineering
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Answer
• Capacity per lane:
– – – – 1 second reaction time 3600 5 C = × = 1500 veh / hour / lane 1 second stop time 1+1 6 3600 seconds per minute Heavy vehicle factor
Road Engineering
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Time headways (2)
• Headway definition for multiple lane facilities • Definition per lane: hi > 0 • Definition for entire roadway: hi ≥ 0
1 n T h = ∑ i =1 hi = n n
Road Engineering
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Distance headways （车头间距）
• Distance headway si: difference between positions vehicle i-1 and i at time t (more complex to measure) • Gross distance headway and net distance headway
Driver behavior
Interaction
Road Engineering
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Vehicle trajectories (车辆轨迹)
• Positions xi(t) along roadway of vehicle i at time t • All microscopic and macroscopic characteristics can be determined from trajectories! • In reality, trajectory information is rarely available • Nevertheless, trajectories are the most important unit of analysis is traffic flow theory
• Why is important the performance of automobile? • Vehicle types, size, weight? • Driving force &am
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Outline
• Traffic Flow Theory（交通流理论） 交通流理论） • Fundamental diagram（交通流基本图） 交通流基本图） • Capacity & LOS (Level Of Service)（服务水平） 服务水平）
• Hours per day
– 3 hour morning peak + 3 hour afternoon peak: 6 – Daytime off-peak: (14-6)x0.5 = 4 – Night time: 10 x0.2 = 2
• Volume:
Road Engineering
1500 × 4 × 2 × 12 = 144,000
s= 1 m X s = ∑ i m m i =1
Road Engineering
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Distance headways (3)
Road Engineering
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Local, instantaneous and generalized
Generalized measuments determined for time-space region Instantaneous measurements collected at t = 20
Road Engineering
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Time headways (3)
• Headways are time/local microscopic variables (collected at cross-section x0) • Mean headway for certain period T of the n vehicles that have passed cross-section x0
Road Engineering
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Time headways （车头时距）
• Time headway hi: passage time difference rear bumper vehicle i-1 and i at cross-section x (easy to measure)
m k= = X
1 = = m 1 m s s ∑ i=1 i s ∑ i m i =1
m
1
Road Engineering
• Also referred to as concentration • How can density be measured? • Now how about speeds?
Road Engineering
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Distance headways (2)
• Distance headway: space/instantaneous microscopic variable • Space-mean distance headway of m vehicles at time instant t for roadway of length X
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Mean speeds
• Local / time mean speed
– speeds vi of vehicles passing a cross-section x during period T
uL = 1 n v ∑ i =1 i n
• Instantaneous / space mean speed
Road Engineering
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●：Haze/Smog weather
Road Engineering
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●：Haze/Smog weather
Road Engineering
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Overview of Vehicle performance
– speed vj of vehicles present at road section at given moment t 1 m
d xi ( t ) dt
vi ( t ) =
d2 ai ( t ) = 2 xi ( t ) dt
Speed Velocity
Road Engineering
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Applications of multiple trajectories
• Exercise with trajectories by drawing a number of them for different situations – Acceleration, deceleration, – Period of constant speed, – Stopped vehicles – Etc.
Road Engineering
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Traffic flow theory
• Traffic flow theory pertains to The Knowledge of Fundamental Traffic Flow Characteristics and Associated Analytical Techniques • Analytical framework: traffic demand, supply and control information into predicted traffic performance indicators
Traffic demand Transport supply Traffic control
Road Engineering
Characteristics and analysis
Traffic performance
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Macroscopic and microscopic characteristics