Volume
VolumeThis selection provides several options which bring up the Volume dialog box with its various data entry screens. Select a screen by clicking its tab at the top of the box. Most of these are self explanatory.
The Volume screen is where the base (existing) volumes are entered, along with the count date if desired. If the “Volume Count Date” box is checked, this date will be printed on the output reports. On the Volume screen a text field is provided for entering the time period for the volumes. This field is always printed on the reports. If time periods are not desired, this field can be used for anything the user wishes or it can be left blank. There is also a field for Sneakers (left turning vehicles that enter the intersection at the end of a permitted LT phase). This volume screen also allows the user to “transpose” a volume from another location. By selecting Index instead of volume, the user can “import” a base volume from another node. In the example illustrated in Figure 41 Intersection Volume Dialog Box, the NB through movement base will be derived from the WB left turn movement at node index #423. This feature will help users incorporate complex intersection geometries into their analysis, and it is anticipated that this feature will allow a parallel analysis of a network contiguous intersection, with a non-contiguous index referencing node with a different control type.
Figure 41 Intersection Volume Dialog Box
The Ped and Bike Volume screen allows the user to enter pedestrian data and segregate bicycle volume information from the motor vehicle count data. The 2000 HCM now includes bicycle approach volumes in the calculation of saturation flow rates. While the HCM does not make a specific distinction between bicycles making through movements versus those making left-turns and right turns, TRAFFIX provides a placeholder where this information can be stored. For analysis purposes, these movement specific bicycle volumes are then aggregated to determine the appropriate approach volume. Likewise the pedestrian volume data input is keyed to the location of the occupied crosswalk. TRAFFIX automatically calculates the conflicts of these “Ped Vol” pedestrian volumes on the turning movements from the adjacent approaches. This dialog box also includes a variable for the “Ped Walk Speed”. TRAFFIX assumes the average walking speed to be 4.00 mile per hour.
Figure 42 Ped and Bicycle Dialog Box
In the Volume Adjustment screen, the user can enter adjustment factors to account for intersection-specific conditions or traffic patterns. The user can also turn on/off the use of the MLF (multi-lane factor) to adjust volumes. If the intersection’s critical V/C is high, the use of MLF should be turned off to more accurately represent likely peak hour operations. Note: For the 2000 and 1997 HCM methodologies, the MLF is applied during the saturation flow calculation, and it is turned on/off in the Geometry…HCM Saturation Calc Input dialog screen. The MLF selection in this Volume dialog screen has no effect on the 2000 or 1997 HCM calculations.
The PHF screen is where the Peak Hour Factors are entered. These values can be applied to the entire intersection, at the movement level, or both.
The Growth Adjustment Factor screen is where expected background growth (or reduction) in existing traffic volume levels can be accounted for. (There is also a global growth factor that can be entered from the Global Data…Titles & Parameters dialog box.) For adjustment factors, the user can enter movement-by-movement adjustment factors, or a single factor to be applied to all movements at the intersection, or both.
Base and Future: These screens allow the user to insert volume reductions for the right and left turn movements. Note that separate screens exist for the base and future conditions. The primary purpose of the right turn reduction is to account for right turns on red. The user has the option of entering a reduction factor on the Volume Adjustment dialog screen or entering the actual number of vehicles to be subtracted on this dialog screen.
The primary use of the left turn reduction is to account for permitted left turns that occur during permitted+protected phasing with exclusive left-turn lanes. The 1985 HCM requires an iterative approach for such conditions, and TRAFFIX requires that the permitted traffic be specified for the use of this methodology. TRAFFIX does not require a volume in this field for the other left-turn control selections for the 1985 HCM methodology or for any of the left-turn control selections for the 1994, 1997 or 2000 HCM methodologies.
Users may find other uses for these fields if they are not needed for the volume reductions described above.
This screen allows the user to enter changes in existing traffic volume patterns that a development is expected to cause due to diversion of existing traffic to the project. The data entry fields on this screen will accept either positive or negative volumes. Thus, the user can subtract a volume from the through movement on an approach and add that same volume to either the left-turn or right-turn movement on that approach. For more information on passerby volumes, see Chapter 20, Section 20.3.
The default heading for the pass-by trips row on the LOS Computation output reports is PasserByVol. Some users prefer to use the passerby volume field for purposes other than accounting for pass-by trips (such as for Approved trips). The user has the option to rename the heading for the pass-by trips row on the LOS Computation output reports. From the Options…Global Data…Titles dialog box, the user’s preference for this title can be entered. This will apply at all intersections for the current scenario, unless the user enters a different heading for an individual intersection here in the Volume…PasserBy Volume dialog screen. All scenarios that share the same Command data set will have the same label for this item.
The volume reductions and the passerby volumes are saved along with the base volume in the *.VOL file if the Write DOS File option is used (located on the Tools menu).