TRAFFIC STUDIES Flashcards
Generally involve time and may entail much cost; therefore it is necessary to plan all data collections carefully
Traffic Studies
These are carried out to analyze traffic characteristics
Traffic Studies
Helps in geometric design and traffic control for a safe and efficient traffic movement
Traffic Studies
Types of Traffic Studies
Volume Studies
Spot Speed Studies
Travel Time and Delay Studies
Conducted to obtain factual information on the number of vehicles and/or persons passing at a specified point on a highway system
Volume Studies
Resulting volume data are expressed in relation to time
Volume Studies
Types of Volume
Annual Traffic
AADT
Hourly Traffic
Short-Term Count
Types of Collected Data for Volume Studies
Mid-block Counts
Directional Counts
Turning/.Intersection Counts
Classification Counts
Cordon Counts
Screen Line Counts
Used to determine annual travel, estimate expected highway user revenue, and compute accident rates
Annual Traffic
Used to measure present demand for service by road, programming capital improvements
Annual Average Daily Traffic (AADT)
Used to evaluate capacity deficiencies, geometric design, or improvement of streets and intersections
Hourly Traffic
Used to estimate maximum flow rate, determine characteristic of peak hour volumes
Short term Count
Total volume counted over one year divided by the number of days in a year
Average Annual Daily Traffic (AADT)
Obtained through traffic volume counts over a number of days (at least 2 days and less than 365 days)
Average Daily Traffic (ADT)
Useful in highway planning and maintenance or repairs of roads but cannot be used for design or operational analysis
Daily Volumes
Identifies vehicle types by number of axles and distance between axles
Classification Counts
Used for determining modal spilt, estimating effects of heavy vehicles on capacity, determining correction factors for automatic counts
Classification Counts
A classified count taken at some points along a line (imaginary) bisecting a given area: man-made or natural barriers are used
Screen Line Counts
Data is used to compare traffic capacities in the path of traffic flow
Screen Line Counts
AKA Road volume data report or Link Counts
Mid-Block Counts
Used for preparing traffic flow maps determining trends
Mid-Block Counts
Measured the total vehicle volume and vehicle classification
Mid-Block Counts
Directional distribution for capacity analysis
Directional Counts
Used for signal timing and justifying traffic control
Directional Counts
Used to determine the number of vehicles and/or persons entering and leaving an enclosed area
Cordon Counts
Includes directional traffic counts at selected sites
Cordon Counts
Enumerates number of left-turn, right-turn, U-turn, and through movements for each approach made by vehicles or pedestrians
Turning Movement Count
Design or improvement of geometry of intersections, signal installation and timing, pavement markings etc
Turning Movement Count
Used for planning turning prohibitions and analyzing high accident intersections
Turning Movement Count
Usually done midnight to midnight
24 hr count
Represents most of daily flow and night traffic
16 hr count
When is a 16 hr count usually done
From 6 am to 10 pm
Covers most of daytime traffic
12 hr count
When is a 12 hr count usually done
From 6 am to 6 pm
Done at time intervals of very high traffic volume
Peak Period Counts
Intervals of 5-15 minutes for about one hour or less
Short Counts
Used to analyze peak hours characteristics
Short Counts
Simplest and most practical method in the absence of any mechanical or automatic counting device
Tallying
Mechanical device useful when volume is high
May be single or multiple type
Manual Counters
Traffic count of very long duration
Used through the use of detectors
Automatic Counters
Counts may be carried out through tallying or manual method while watching video or footage of traffic flow
Video Cameras
Presentation of Traffic Volume
Variations
Traffic Flow Maps
Intersection Diagrams
Spot Speed Studies Objectives:
a) Determine ____ and ____ of speeds as a basis for formulating the design standards
b) Establish ____ and ____ speed limits
c) Determine need for posting ___________
d) Determine need for _________
e) Evaluate performance of a _____ improvement or traffic control device through a ______ study
a) Range; Magnitude
b) Maximum; Minimum
c) Advisory Speed Designs
d) School Zone Protection
e) Geometric; Before and After
Spot Speed Studies Time of Study:
a) Period during which speeds are measured depends on the _____ of the study
b) Duration of the study should be around ____ hour
c) Short study period often lead to bias towards ____ vehicles
a) Purpose
b) One
c) Faster
Radar Speed Meter: The radar is positioned at the ___ of the roadway at an angle of ___ degrees with the ____ and is directed toward the incoming vehicles
Edge
15
Centerline
2 lines, 30-50m, apart are drawn transversely on the pavement
Trap Length Method 1
Common error in most visual methods of surveys
Parallax
Take video of the traffic flor and put markers on roadside or monitor
Trap Length Method 2
Total elapsed time necessary for a vehicle to travel from one point to another over a specified route under existing traffic conditions
Travel Time
Extra time spent by drivers against their expectation
Time is lost to travel because of traffic frictions and control devices
Delay
Data obtained from _____ give a good indication of (performance) level of service on the study section
Travel time and delay studies
Cause of Delay: PED
Pedestrians
Cause of Delay: BP
Buses Un/Loading
Cause of Delay: JB
PUJ Un/Loading
Cause of Delay: PM
parking Manuevers
Cause of Delay: LT
Left Turn
Cause of Delay: PC
Parked Vehicles
Cause of Delay: DP
Double Parking
Cause of Delay: S
Traffic Signal
Cause of Delay: SS
Stop Sign
Cause of Delay: T
General Congestion
Conducted when delay details are unimportant
License Plate Method
