Traffic Operations Analysis Flashcards
(52 cards)
Flow Rate
the number of vehicles that pass a point on a facility per unit of time
when the time unit is one hour or more, the flow rate is referred to as volume
Traffic Demand
the number of vehicles desiring to pass that point during the time period
PHF
relationship between hourly volume and maximum rate of flow within the hour
PHF = 1.0 - consistent flow
Lower PHF means more extreme peak
Speed
distance traveled per unit of time
Time Mean Speed
average speed of all vehicles passing a point over a time period
“spot speed”
Space Mean Speed
average speed of all vehicles occupying a given section of the roadway over a specific time period
Travel Time
the time required to travel a segment of given length
Running Time
total time the vehicle is in motion while traversing a segment of a given length
Density
number of vehicles in a given length of roadway or a lane
Headway
time between successive vehicles passing a point
Spacing
distance between successive vehicles passing a point
Equation for uninterrupted flow
v = S x D
flow = space mean speed x density
PHF Equation
PHF = hourly volume / (4 x peak 15 minute volume)
Capacity
ability of a transportation facility or service to meet the quantity of travel demanded by it
Describe uninterrupted flow
Vehicles are not interrupted by external factors such as traffic signals, stop/yield signs, or access points.
Freeways and long rural segments between controlled intersections.
Describe interrupted flow
Vehicle flow interrupted by factors such as traffic signals, stop/yield signs, frequent intersections/driveways.
Urban streets
Factors that impact capacity
- Lane widths
- Number and use of lanes
- Proximity of obstructions along edge of roadway
- Terrain
- Type of area (urban, suburban, rural)
- Vehicle mix (trucks/buses)
- Driver familiarity
When is No Control an option?
Total entering traffic less than 2000 units/day
Adequate approach sight distance
Three levels of traffic control
Uncontrolled
Stop or Yield
Signal
When is Yield or Two-Way Stop Control an option?
When right-of-way is assigned to the major street and the minor street traffic must stop or yield before proceeding
Total daily traffic on thru street less than 6000 veh/day
Adequate approach sight distance
3 or more crashes susceptible to correction by a stop sign
When should Multi-way Stop Control be considered?
As an interim measure where a traffic signal is justified
5 or more crashes in a 12m period are susceptible to correction
Minimum volumes
- 300 veh/hour over 8 hours on major street
- total entering volume 200 units/hr on minor street, with delay of 30 sec/veh during peak hour
- 70% of above if speed >40 mph
Steps for capacity analysis at signalized intersections
Determine the lane group flow rates
Determine the adjusted saturation flow rate
Determine proportion of traffic arriving on green
Determine capacity
Determine delay
Determine LOS
Access management
proactive management of vehicular access points to land parcels adjacent to raodways
Access management techniques
Access spacing
Driveway spacing
Safe turning lanes
Median treatments
Right-of-way management
