Peak Hour Factor (PHF)
Hourly Volume / 4 x (Peak 15 Minute Volume)
Flow Rate definition
number of vehicles that pass a point on a roadway per unit of time (usually less than 1 hour)
Time Mean Speed (TMS)
average speed of all vehicles passing a point over a specified period of time
TMS = (SUM(d/t)) / n
d = distance
t = time
n = # of cars
*Expressed in mph
(passing a point)
Space Mean Speed (SMS)
average speed of all vehicles occupying a given section of roadway over a specified period of time
SMS = ( n * d) / (SUM(t))
d = distance
t = time
n = # of cars
*Expressed in mph
(over a given section)
Uninterrupted Flow Equation
v = S x D
v = flow (veh/hr)
S = space mean speed (mph)
D = density (veh/mile)
Interrupted Flow or flow
(influenced by)
flow influenced by external factors such as
* traffic signals
* stop or yield signs
* frequent uncontrolled intersections
* high volume driveways
No Control (Uncontrolled Intersection) parameters
- less than 2000 vpd (veh, ped, and bicycle)
- adequate sight distance
- > 5 veh or ped crashes in 3 years; fewer than 3 in 2 years
Yield Control parameters
- Full stop not required
- Adequate sight distance
- less than 6000 vpd (through street)
- < 3 collisions in 1 year; < 5 in 2 years
TWSC parameters
- full stop required
- more than 6000 vpd (through street)
- sight distance NOT adequate
- > = 3 crashes 1 year, >= 5 crashes in 2 years
AWSC Warrants
- interim to traffic signal
- > =5 crashes in 12-month period
- Minimum 8 hour volumes
>= 300 vph on major street, >= 200 combined vehicular, pedestrian, and bicycle on minor street, average delay >= 30 seconds
Lane Group Capacity
(Signalized intersection equation)
c = N x s x (g/C)
c = capacity
N = # of lanes
s = saturation flow rate
g/c = ratio green time to overall cycle length
Delay equation (signalized intersection)
d = d1 + d2 + d3
d = control delay (s/veh)
d1 = uniform delay
d2 = incremental delay
d3 = inital queue delay
Systems interchange
connect controlled access highways
ex: directional, clover leafs (NO STOPPING)
Service interchange
connect a higher functional class road to a lower functional class road
ex: diamonds, diverging diamonds (MUST YIELD STOP)
Free Flow Speed
equation
FFS = 75.4 + flw + flc - 3.22TRD^0.84
FFS = free flow speed (mph)
flw = adjustment for lane width (mph)
flc = adjustment for right-side lateral clearance (mph)
TRD = total ramp density (ramps/mi)
flow / density equations
v = S x D
D = v / s
v = flow (veh/h)
S = space mean speed (mph)
D = density (veh/mi)
TDM
what is it’s overall goal?
- Transportation demand management
- aims to INFLUENCE PEOPLE’S BEHAVIOR
- focuses on travel demand (traveler) rather than transportation supply (travel facilities)
ISD equation
ISD = 1.47 V x tg
ISD = intersection sight distance along major street (ft)
V = speed of traffic on major street (mph)
tg = time gap (sec)
Recommended Vehicle Time Gap
7.5 seconds
for passenger cars making left turns onto a 2-lane major roadway w/ level grades
“road diets”
- traffic calming approach involving reduction in width or number of vehicle travel lanes
- reallocates for bicycle lanes, ped crossing islands, left turn lanes, or parking
conflict points of 4-leg intersection
32
What determines
LOS for weaving section?
- average running speed
- density
conflict points (t-intersection)
9
Convert flow rate to vph
= 200 veh / 15 mins
= 800 veh / hr
