1. Vehicle Flow

2. Homework
Ch 5 # 1, 2, 4, 7, 9

3. Vehicle Flow How do vehicles operate in the system capacity speed
headway
density

4. Time Space Diagrams Show vehicle location vs. Time one way or two way
any type of transportation system
used to find
siding placement
progression
minimum headways
Throughput

6. Vehicle Following
Spacing needed for stopping

7. Deceleration 3 types of deceleration Initial spacing
Normal dn = 8fps^2
Emergency de = 24fps^2
Instantaneous
Initial spacing
S = vd +v^2/2df –v^2/2dl +NL +x0
Safest spacing when lead vehicle decelerates instantaneously and following vehicle brakes at normal deceleration

8. Example
What is the safe initial spacing between two vehicles traveling 40 mph if the lead vehicle uses an emergency deceleration of 24 fps^2 and the following vehicle normally decelerates at 8 fps^2? PR time = 1.5 sec, vehicle length = 20 feet, x0 = 4 feet

9. Flow Concepts
4 variables
volume
speed
density
headway

10. Volume # of vehicles passing a given point in a given unit time
q = n/T
cars per hour
does not tell you anything about speed or density

11. Speed 2 types Space Mean Speed Time Mean Speed
distance divided by time
useful in determining vehicle flow characteristics
Time Mean Speed
Spot speeds
Radar gun
not useful except for tickets

12. Example
Si = 2 miles, i = 1 - 4
v1 = 42 mph, v2 = 39 mph, v3 = 47 mph, v4 = 50 mph
Average V = 44.5 mph
m1 = 3.1 min, m2 = 2.8 min, m3 = 3.3 min, m4 = 3.0 min
Average = 39.5 mph
What is the difference, is it significant?

13. Density
Concentration
vehicles per unit length
cars/mile

14. Headway Time or distance between two vehicles
h = 1/q gives the time headway
h = 1/k gives distance headway
which is more useful?

15. Relationships q=uk Important points basic relationship jam density
jam speed
max volume

16. Relationships

17. Relationships

18. Relationships

19. Relationships
Shape of curves
what do they tell us?

20. Example The u-k relationship is u + 2.6 = 0.001(k – 240)^2
Find umax, jam density, and max capacity

21. Shock waves
Happens when traffic is forced to change speed either slowing down or speeding up
shockwave
Can move either forward or backward
usw = (qb – qa)/(kb – ka)
a, b are 2 points of interest
If shockwave is + => heading in direction of flow
If shockwave is 0 => stationary
If shockwave is - => moving against flow

22. Example
A line of traffic, moving at 30 mph and a concentration of 50 veh/mi is stopped for 30 sec at a red light. Calculate the velocity and direction of the stopping wave, the length of the line of cars stopped during the 30 sec of red, and the number of cars stopped during the 30 sec of red. Assume a jam capacity of 250 veh/mi

23. Control of Vehicle Flows
Control vehicles
minimize accidents
maximize effectiveness
transit
airports
roadways
Channelization most common control

24. Control of Vehicle Flows
Speed limits
Control on Links
signage
lane width
number of lanes
headway rules

25. Headway Rules
RR - uses block system

26. Headway Rules Aircraft Airports 1 aircraft on runway at any time
separation distances
2.5 miles between aircraft
10 miles horizontal / 2000 ft vertical in air
Control based on aircraft location
Ground control for aircraft not on runway

27. Capacity Capacity based on mode # of vehicles per hour
# of passengers per hour
arrivals, departures per hour

28. Highways Capacity varies by road type All use Level of Service
Freeways
no controls,
Intersections
traffic control
2 lane & 4 lane roads
lead vehicle
All use Level of Service

29. Determining Capacity
Based on Roadway geometrics and traffic conditions
For Freeways
can determine ideal conditions and from that a maximum capacity

30. Peak Hour Factor
Measures demand peaking

31. Level of Service LOS can be based on 6 LOS A - F delay per vehicle
speed
service flow
6 LOS A - F
A is best
F is worst

32. Freeway Capacity LOS based on
density
speed
v/c
For an LOS can find Maximum Service Flow (MSF)

33. MSF MSF = qmax*(v/c) - ideal conditions SF = q = qmax*N*fw*FHV
Table for heavy vehicle factors
Table for width factors

34. Capacity Restrictions
Non recurring
Recurring

35. Example
Ch 4 # 14

36. Pedestrians
LOS based on
speed
flow rate
v/c ratio

37. Bike LOS
Based on amount of hindrance

38. Airports Capacity depends on landside and airside
LOS is based on delay and total time
Why are airports becoming shopping malls?

39. Rail Mass transit AMTRAK LOS based on pass/seat, space/ pass,
both peak and off peak
AMTRAK
LOS based on wait time, comfort, pass/seat