Traffic Parameters
Traffic Parameters
CE 361 Transportation Engineering
Three Main Parameters
Three Main Parameters
• Flow, Q
Flow Q
– Vehicles per hour
• Density, K
Density K
– Vehicles per mile
• Speed, V
– Miles per hour
• Basic Equation of Traffic Engineering
– Q = K x V
Q
Speed (mph)
Q‐K‐V
Q
K V Relationships
Relationships
Vf
Km
Vm
Vm
KJ
Flow (vp
ph)
Vm
Qm
Qm
Kj
Flow
Vf
Qm = Max Flow or Capacity = Max Flow or Capacity
Vf= Free Flow Speed
Vm= Optimal Speed under Max Flow
Kj = Jam Density
Km= Optimal Density under Max Flow
Km
Density
KJ
Level of Service (Flow Rate Limits) General Rules of Thumb
l l
f h b
Level of Service
A
Free‐Flow
Free
Flow
B
Reasonably
Free‐Flow
C
Operation Stable But Becoming Critical
D
Lower Range of Stable
E
Unstable
F
Forced Flow
Controlled‐Access Hi h
Highways
Multilane Rural without Access ith t A
Control
Two Lane Roadways
700 vehicles per hour per lane
per lane
720 vehicles per hour 420 vehicles per hour per lane
per lane
total two way
total two‐way
1120 vehicles per hour per lane
1200 vehicles per hour per lane
750 vehicles per hour total two‐way
1640 vehicles per hour per lane
1650 vehicles per hour per lane
1200 vehicles per hour total two‐way
2015 vehicles per hour 2015
vehicles per hour
per lane
1940 vehicles per 1940
vehicles per
hour per lane
1800 vehicles per 1800
vehicles per
hour total two‐way
2200 vehicles per hour per lane
p
2200 vehicles per hour per lane
p
2800 vehicles per hour total two‐wayy
Greater than E Limit
Greater than E Limit
Greater than E Limit
Other Terms
Other Terms
• ADT: Average Daily Traffic
ADT: Average Daily Traffic
• AADT: Average Annual Daily Traffic
AADT: Average Annual Daily Traffic
• AWT: Average Weekday Traffic
AWT A
W kd T ffi
• AAWT: Average Annual Weekday Traffic
Peak 15‐Minute
Peak 15
Minute Volume
Volume
• Example
– Peak 15‐minute volume = 750 vehicles
– Maximum Flow Rate = 15‐minute volume * 4
Maximum Flow Rate = 15 minute volume * 4
• Maximum Flow Rate = 750 * 4 = 3000 veh per hour
Peak Hour Factor
Peak Hour Factor
Hourly
H
l Volume
V l
HV
PHF =
=
Max Rate of Flow 4 × V15
– Where HV = Hourly Volume, vph
– V15 = max. 15‐minute volume within the hour
= max 15 minute volume within the hour
PHF Example
PHF Example
• Collected Data
Collected Data
Time Interval
7:15-7:30 AM
7:30-7:45 AM
7:45-8 AM
8-8:15 AM
Volume
(
(veh)
)
450
498
604
437
– HV = 450 + 498 + 604 + 437= 1989 vph
– V15 = 604 veh, 7:45‐8 AM
604 veh, 7:45 8 AM
– PHF = 1989 / (4*604) = 0.823
Directional Design Hourly Volume
• DDHV = AADT x K X D
DDHV = AADT x K X D
– K: 0.1 for Urban, 0.2 for Rural
– D: 0.5 for Urban, 0.65 for Rural
D: 0 5 for Urban 0 65 for Rural
• Number of Lanes by Direction = DDHV/SFRL
N b
fL
b Di ti
DDHV/SFRL