PerRoad:  Traffic Inputs

Traffic data are entered into PerRoad in terms of load spectra (distribution of axle types and weights).  The input box shown below is the main traffic input window.  The particular inputs are outlined in the steps below.

The general traffic data input group is shown in the figure below and definitions of each terms are provided thereafter.

Two-Way AADT:  Current average annual daily traffic.  This parameter represents the total amount of traffic traveling in both directions using all the lanes.  Most state departments of transportation maintain GIS-based systems that can be used to obtain this information.

% Trucks:  The percent of AADT that is comprised of trucks.  In PerRoad, trucks refere to FHWA class 4 through 13 vehicles.

% Trucks in Design Lane:  The proportion of trucks, in the design direction, using the design lane.

Axle Groups/Day:  This parameter represents the current number of axle groups in the design direction, and design lane.  This value is computed automatically when using the “Input Load Spectra by Vehicle Type.”

% Truck Growth:  The estimated growth rate for traffic.  PerRoad assumes a compounding interest rate formula to compute the total traffic applied over the life of the structure.

Directional Distribution:  The proportion of traffic traveling in the design direction.  This is typically 50%, though some special cases, may require higher or lower percentages.

Input Load Spectra by Vehicle Type:  Use this feature to quickly enter or select a default vehicle type distribution which will automatically compute the frequency of axle types and load distributions for each axle (see next step).

Clicking on the Input Load Spectra by Vehicle Type will launch the input window shown below.  The Roadway Functional Classification drop-down box allows you to select the roadway type which will automatically load a default vehicle distribution.  The %AADTT indicates the percentage of each truck type and the total must sum to 100%.  Each vehicle type also has a default number of axle types per vehicle.  You may use the defaults or enter more specific information if you have it available.  After clicking Accept Changes in this box, you will see that the axle load distribution data have been updated when you return to the Loading Conditions input box.

You must specify the expected percentage of each axle type.  If you already completed Step 2, then these values have already been computed based on the vehicle types and number of axles per vehicle.  Alternatively, you can also simply enter the values directly and the sum should equal 100%.  These percentages will be used in the Monte Carlo simulation to represent the actual expected traffic and generate a distribution of pavement responses.  The Current Configuration drop down box indicates what data the table below is displaying and also allows you to control which configuration is being displayed.  Clicking in any of the percentage windows will also update the current configuration display.  For definitions of the axle types, click here.

You must specify the expected percentage of each axle weight, by axle type.  If you already completed Steps 2 and 3, this has already been done for you using default load distributions.  Alternatively, you can also simply enter the values directly and the sum should equal 100% for each axle type.  The weight ranges are given in 2,000 lb (2 kip) increments.  These percentages will be used in the Monte Carlo simulation to represent the actual expected load spectra and generate a distribution of pavement responses.  The Current Configuration drop down box indicates what data is displayed in this table and also allows you to control which configuration is being displayed.