Chapter 3. Volume, Density & Speed Studies and Characteristics

1. Chapter 3. Volume, Density & Speed Studies and Characteristics • Volume (rate of flow) --- intensity of traffic movement • Speed --- motion condition • Density --- distribution of traffic flow over space • Relationship among three parameters --- mathematical equations

2. 3.1 Definition of Volumes • 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.

3. Some useful volumes • 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

6. 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.)

7. Calibration of Monthly Variation Factors • Monthly variation factor (MF) --- is defined as ratio of AADT over ADT for particular month of the year

8. 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

9. 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

10. 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

11. 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!!!

12. Peak-Hour-Factor (PHF)

13. 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

14. 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!!!

16. 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

17. 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