Notes for 1985 HCM Method

Right Turns

The right turn treatment is specified in the pop-up Geometry…Critical Gap screen, when the 1985 HCM method is selected. The user must indicate the treatment for the right turns. Four choices are available in the 1985 method:

Include	Right turns are included in all calculations.
Ignore	Right turns are excluded from all calculations.
Channelized	The major street right turns are channelized so that they do not conflict with left turns from the opposite approach seeking to enter the same street. The right turns are excluded from the conflicting volume computation for the left turn capacity analysis. The right turns however are included in the conflicting volume computation for the cross-street movements.
Acceleration	An acceleration lane is provided on the major street for right turns to accelerate up to speed. This reduces the critical gap for minor street right turns.

PCE and Grade Adjustments

Same as 1994 HCM method.

Critical Gap

The user enters data and adjustment factors for computing the critical gap for each movement in the pop-up Geometry…Critical Gap screen. The “Adj.” fields allow the user to specify how many seconds to add or subtract from the computed critical gap. The right turn “Radius” and “Angle” fields allow the user to specify these items for use by TRAFFIX™ in computing additional adjustments to the critical gap (see Table 10-2, pg. 10-7 of 1985 HCM for details).

Notes for 1994 HCM Method

Time Period

If the 1994 method is selected, then the user must input the analysis time period (T) in terms of hours for the purpose of calculating delay (see page 10-12, 1994 HCM).

Right Turns

The user must then indicate the treatment for the right turns. Three choices are available:

Include	Right turns are included in all calculations.
Ignore	Right turns are included in all calculations.
Channelized	The major street right turns are channelized so that they do not conflict with left turns from the opposite approach seeking to enter the same street. The right turns are excluded from the conflicting volume computation for the left turn capacity analysis. The right turns however are included in the conflicting volume computation for the cross-street movements.

PCE Adjustments:

The default PCE factors are shown in Table 10-1, page 10-6 of the 1994 HCM. The user can specify a different vehicle mix by turning “ON” the “Vehicle Type” field in the pop-up Geometry…PCE screen. New fields are then shown which allow the user to specify the proportions (must sum to 1.00) of vehicles by each vehicle type.

Grade

The user enters grades for each approach to the intersection in the pop-up Geometry…PCE screen. Use the drop-down box to choose from the available selections. A “plus” grade means the vehicles must climb up hill to reach the intersection.

Critical Gap:

Both the 1994 and 1985 HCM methods allow the user to adjust the critical gap on the Geometry…Critical Gap screen.