HCS Analysis

This section discusses the use of the Highway Capacity Software program to perform analysis of interchange and freeway operations reflective of different design alternatives and traffic volumes. The two key modules that will examined in the documentation include the FREEWAY OPERATIONS and the RAMPS. For each of these two, examples will be provided showing the traffic and geometry of the facility and the corresponding screens from the Highway Capacity Software will be provided to serve a guide for entering the information.

The first key item in performing the HCS analysis is determination of the traffic conditions that result from the interchange. Obtaining the traffic information on a 24-hour basis is discussed in more detail in the GIS-Tranplan section of the documentation. To use the traffic volumes within the HCS program, it is necessary to convert the volumes from the 24-hour basis to a peak period (hour) basis. An easy method for accomplishing this is to factor all the volumes by a 10-12 percent. This will provide a decent estimate of the peak period flows. If more detailed modeling is performed to obtain traffic estimates from the peak period based on trip purposes then the user should use this improved traffic data.

For the examples shown in this section, the traffic conditions are as follows:

  Existing Conditions             After Conditions

Factoring the turning movement volume to represent the peak period for the model (using a simple 10% factoring method) the new volumes that will be used in the analysis are:

  Existing Conditions             After Conditions

As mentioned, there are two Highway Capacity Analysis that will be examined with respect to interchange justification: freeway operation and ramps. For the case study, the section of freeway east of the interchange will be examined in the FREEWAY OPERATIONS section and the two ramps leading to and coming from the east will be examined. At this point, the user should select the appropriate HCS tool to examine for the case study.

                    

     Select any of the options to receive more information or click on the back button to return to the main interchange justification page or the site map button to go to the site map.