1. Macroscopic Speed Characteristics
Chapter 5
Macroscopic Speed Characteristics
거시적 속도 특성

2. Introduction Macroscopic speed characteristics
Speed characteristics of vehicle groups passing a point or short segment
Speed & travel times is a fundamental measurement of the traffic performance
Many analysis and sim. models predict speed as the performance measure given the design, demand, and control
Speed is used as an indication of LOS, in accident analysis, and in most engineering studies
 Analyst must be familiar with speed characteristics and associated statistical analysis techniques

3. 5.1 Speed and Travel Time Variations

4. Temporal Variations Influencing factors for Temporal variations
Traffic flow intensity
Flow rate or flow-capacity ratio
Vehicle mix, driver mix, lighting, weather, and incidents
Design speed & speed limits influence the upper limit on speed

5. Temporal Variations
Fig 5.1

6. Temporal Variations
Fig 5.2

7. Temporal Variations
Fig 5.3

8. Spatial Variations Variation between lanes
 Fig 5.5
Variation between directions of travel
For divided highways, speeds are different due to differences in flows, designs, or controls
Traffic conditions in other direction may influence  Incidents ; passing(2-lane 2-way)
Longitudinal variation due to changes in demand, geometric design, control
 Fig 5.6, 5.7

9. Spatial Variations
Fig 5.5

10. Spatial Variations
Fig 5.6 & Fig 5.7

11. Modal Variations
Fig. 5.8

12. 5.2 Importance of Mean-Variance Relationships

13. Coefficient of Variation
Coefficient of Variation of a distribution of individually measured speeds
C.V. is a measure of dispersion & means of “normalizing” the standard deviation
 For example, 3 mph standard deviation is considered small when mean=60mph (C.V.=0.05)compared to when mean=15mph(C.V.=0.20)

14. Time-Mean-Speed & Space-Mean-Speed
The term “mean speed” we have been using
 Time mean speed (Spot speed)
Individual speed first converted to individual travel time rates to calculate the average speed  Space mean speed

15. Example of Difference 3 vehicles pass a point at 30, 60, 60 mph
2 vehicles (one 60mph and another 30mph) traveling on a 1-mile track ;
An observer standing at a point would record 60 vehicles traveling at 60mph and 30 vehicles at 30mph over 1 hour
2 consecutive aerial photographs taken 60 (1-min)seconds apart

16. Relationship between 2 Speeds
Equation (Wardrop, 1952)
In the circular track example :
Space mean speed = 45 mph
Variance = 225
Condition for Space mean=Time mean
Variance of space mean=0  All vehicles travel at the same speed
If variance > 0(as in reality) ;
 Space mean < Time mean (Always!)

17. 5.3 Travel Time & Delay Study Techniques

18. Travel Time Information is needed for :
Assessment of operational problems
Signal control coordination
Traffic assignment
Economic studies
Before-and-after studies

19. Travel Time Study Techniques
License Plate Technique
The license plate number is recorded with the entry and exit times (to obtain travel time between two points in the highway system)
The plate numbers are matched, and elapsed times are determined
Stop watch, Tape recorders and matching program are available
Sample size required
Generally 50 to 100
Exact sample size determined statistically  Eq. 5.10
OD information can also be obtained

20. Test Vehicle Technique
* Most popular method
A vehicle placed in the traffic stream travels as the “average” vehicle
Under low volume, difficulty exists
Sample size
5 to 50 test runs
Variations(종류) of the test vehicle method
Travel time contour map
Estimate trip times from center to various locations in a metro area
Annual base measurement  trends in TT
In fig 5.13; during downtown home trips (PM peak), drivers recorded their locations at 15 min intervals

21. Travel Time Contour Map
Fig 5.13

22. Speed Contour Map
Identify bottlenecks and resulting queueing patterns on urban freeways
Speedometer reading
Test vehicle launched every min
Reading at 0.2 mile intervals when speeds>30 mph
Reading at 0.1 mile intervals when speeds<30 mph
Trajectory and speedometer reading recorded on time space diagram
Construct contour line just above the speed at capcity flow(40mph) and just below the speed at capacity flow (30 mph)
Above 40mph : free flow (Green)
Between 40 and 30 : transitional (Yellow)
Below 30 mph : congested (Red)

23. Flow-travel time variation (Moving vehicle method)
Useful when determining total veh-miles and veh-hours of travel
Travel time + Flow information
Travel time recording in each direction
Three vehicle counts
# of opposing vehicles met
# of veh overtaking the test vehicle
# of veh passed by the test vehicle
Estimation of hourly flow

24. Speed Contour Map
Fig T/S diagram

25. Intersection Delay Study
Total Delay Measurement
Affected TT – Unaffected TT
(Accel/decel lost time + stopped delay)
Establish a distance of travel and an unaffected cruise speed
Record actual TT (affected TT) and compare with unaffected TT
Stopped Delay Measurement
(Stopped veh count method)
Count the # of stopped veh at regular time intervals (10-20 sec, not a multiple of green phase or cycle)
Stopped delay = avg. # of stopped veh x time interval x 0.92 (adjustment factor)
Total Delay = Stopped delay x 1.3

26. Homework