Chapter 3. Volume, Density & Speed Studies and Characteristics

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Chapter 3. Volume, Density & Speed Studies and Characteristics

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Chapter 3. Volume, Density & Speed Studies and Characteristics

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- Volume (rate of flow) --- intensity of traffic movement
- Speed --- motion condition
- Density --- distribution of traffic flow over space
- Relationship among three parameters --- mathematical equations

- Volume --- is defined as the number of vehicles that pass a point on a highway, or a given lane or direction of a highway, during a specified time interval, generally a day or an hour.

- AADT (Average Annual Daily Traffic 年平均日交通量)
- AAWT (Average Annual Weekday Traffic 年平均工作日交通量)
- ADT (Average Daily Traffic 平均日交通量)
- AWT (Average Weekday Traffic 平均工作日交通量)

These four volumes remain at macroscopic level

Calibration of Daily Variation Factors

- Daily variation factor (DF) --- is defined as ratio of AADT over yearly average volume for particular day of week (Monday, Tuesday etc.)

Calibration of Monthly Variation Factors

- Monthly variation factor (MF) --- is defined as ratio of AADT over ADT for particular month of the year

- Hourly volumes and peak hour volume （小时流量，高峰小时流量）
- Hourly volumes are used to reflect variation (fluctuation) of traffic volume in a day
- Peak hour volume is defined as the volume in the single hour that has the highest hourly volume

- Rate of flow(流率）--- defined as an equivalent hourly volume for a given interval (interval can be 5, 10, 15 minutes)
- used in design to reflect the worst scenario
- used in modeling mathematical relationship among parameters in research
- generally the shorter the interval the higher the rate of flow

Interval Volume Interval Volume

7:00 – 7:05 15 7:30 – 7:35 17

7:05 – 7:10 25 7:35 – 7:40 35

7:10 – 7:15 18 7:40 – 7:45 28

7:15 – 7:20 42 7:45 – 7:50 32

7:20 – 7:25 31 7:50 – 7:55 26

7:25 – 7:30 18 7:55 – 8:00 20

V5 = (180, 300, 216, 504, 372, 216, 204, 420, 336, 384, 312, 240)

V10=(240, 360, 294, 312, 360, 276)

V15=(232, 364, 320, 312)

Max V5 = 504; Max V10 = 360; Max V15 = 364

Hourly volume = 307

- Peak hour factor（高峰小时系数）--- is defined as the ratio of hourly volume divided by maximum rate of flow

PHF5 = 307/504 = 0.61;

PHF10 = 307/360 = 0.85;

PHF15 = 307/364 = 0.84;

PHF is used to reflect the fluctuation of

volume distribution in an hour!!!

Peak-Hour-Factor (PHF)

- The 30th hourly volume(第30位小时交通量) --- defined as an hourly volume at which its ranking on yearly-counting curve counts 30th among 8760 hourly volumes in a year
- DDHV (Directional Design Hourly Volume 设计小时流量) --- DDHV = AADTⅹK ⅹD where: K is proportion of daily traffic occurring during the peak hour, expressed as a decimal; D is proportion of peak-hour traffic traveling in the peak direction, expressed as a decimal

Relationship Between DDHV and AADT

- D= ratio of design hour volume in the major direction to the total (方向性系数）

- K=ratio of design hour volume to the 24 hour volume （设计小时系数）

In general D and K isconstant!!!

Estimation of Vehicle-Miles Traveled on a Limited Network: An Example

- VMT (Vehicle Miles Traveled=车英里) or VKT(Vehicle Kilometers Traveled 车公里) --- defined as a product of number of vehicles and miles (or kilometer) traveled by these vehicles

- PCE and PCU（小汽车当量）--- defined as the number of passenger cars displaced by one truck, bus, or RV in a given traffic stream
- Traffic intensity can be used as criterion to determine passenger car equivalent