Traffic Volume Studies

Traffic Studies

• Traffic studies are split into inventories, administrative studies, and dynamic studies.

Volume Study

• Traffic volume refers to how many vehicles use a section of road in a select period.
• Traffic volume can be measured from 15-minute intervals up to a year depending on the data's use.

Objectives of Traffic Volume Studies

• Determine vehicle composition in traffic
• Determine service flow rate in PCU/PCE
• Estimate ADT based on expansion factor
• Determine directional distribution (DD)
• Draw flow fluctuation curves

Scope of Traffic Volume Studies

• Traffic volume studies can gauge the effectiveness of a traffic control measure
• They help evaluate the operating conditions of a road
• They help plan traffic operation and control of existing facilities
• They help design intersections, signal timings, and channelization
• Assist in structural design of pavements, geometric design, and establishing road capacity

Applications of Volume Studies

• Volume studies provide insight into:
  • Average Annual Daily Traffic (AADT)
  • Average Daily Traffic (ADT)
  • Peak Hour Volume (PHV)
  • Vehicle Classification (VC)
  • Vehicle Miles of Travel (VMT)

Key Parameters & Definitions

• Volume: The number of vehicles passing a measurement point during a specified time frame.
• Demand: Measures the number of vehicles or people waiting for service at a given time.
• Capacity: The maximum number that can reasonably be served in a given time period.
• Passenger Car Equivalent (PCE): The impact a mode of transport has on traffic variables such as headway, speed and density, compared to a single car.
• Passenger Car Unit (PCU): A vehicle unit that is used to express highway capacity.

Daily Volume Parameters

• Average Annual Daily Traffic (AADT): Average of 24-hour counts collected every day of the year.
• Average Daily Traffic (ADT): Average of 24-hour counts collected over a number of days greater than one but less than a year.
• Peak Hour Volume (PHV): The maximum number of vehicles that pass a point on a highway during 60 consecutive minutes.
• Vehicle Classification (VC): Categorization based on vehicle type, like cars, two-axle trucks, or three-axle trucks.
• Flow Rate: Number of vehicles in a 15-minute interval, expanded to an hourly rate.

Methods of Counting Traffic Volume

• Three main methods:
  • Manual observation
  • Automatic recording
  • Car moving

Manual Observation

• Manual counts are used for small data samples.
• They are used when automated equipment is not required.
• Conducted for at least two hours during peak traffic, dividing the hours into 15-minute intervals and recording each class of vehicle.
• It is well suited to recording the number of Motorbikes, PC's, Mini buses, Busses, Travel Busses, Trucks and trucks w/ trailers.

Advantages of Manual Observation

• Vehicle classifications can be determined
• Very accurate
• Less expensive

Disadvantages of Manual Observation

• Depends on people
• Cannot be use for long periods
• Can be affected by weather

Automatic Recording

• Automatic recording can be achieved via:
  • Electric plate
  • Pneumatic tube counter
  • Magnetic field
  • Video recording

Advantages of Automatic Recording

• Suitable for long periods
• Not affected by climatic conditions

Disadvantages of Automatic Recording

• High cost
• Vehicle type is not specified
• Affected by electric current
• The count is not accurate

Example Traffic Study

• An inventory on Thursday, March 14th, 2011, between 8 am and 10 am in the capital counted 500 equivalent vehicles.
• From 8 am to 10 am, traffic volume represented 12.4% of the 16-hour traffic, between 6 am and midnight.
• The 16-hour traffic volume represented 90% of the daily traffic.
• Thursday traffic represented 15% of the week’s traffic.
• The month of March accounted for 9% of the annual traffic.
• With the available information, one can find:
  • Average Daily Traffic (ADT)
  • Annual traffic average
  • Annual Average Daily Traffic (AADT)
  • Projected traffic volume for 2031, considering an annual growth rate of 7%

Traffic Volume Calculations

• Considering a 16 hour traffic volume of 500:
  • Traffic volume during the 16 hours = 500 * (100/12.4) = 4032 vehicles.
  • Average Daily Traffic (ADT) = 4032 * (100/90) = 4480 vehicles per day.
  • Average weekly traffic = 4480 * (100/15) = 29867 vehicles per week.
  • Average traffic during March = 29867 * 4 = 119468 vehicles per month.
  • Annual average of traffic = 119468 * (100/9) = 1327422 vehicles per year (2011).
  • Annual Average Daily Traffic (AADT) = 1327422 / 365 = 3637 vehicles per day (2011).
  • Traffic volume for 2031 (7% growth rate) = 3637 * (1 +0.07)^20 = 14074 vehicles per day (2031).
  • Where 'e' is the annual growth rate, and 'n' is the number of years.