Allows the fastest paths for the roundabout to be dynamically calculated, and then placed in the drawing and/or saved to a file.

The fastest path is the largest possible radii centerline path approximated based on the critical offsets (entry median offset, entry edge offset, central island offset, exit median offset, and exit edge offset) for the through path or turn path (for more information on the fastest path, see Overview -> Fastest Path).

Note:

• For the purposes of describing the software, it is assumed that Right-Hand Traffic is selected under Traffic Direction in Design Guidelines' General Category. If Left-Hand Traffic is selected, the descriptions with references to a right/left turn path should be interpreted in the opposite direction.
• The fastest through path will only be calculated/generated if the angle measured counterclockwise (for right-hand traffic) between the entry and exit reference geometry is between 135 and 225 degrees.

Dynamic Fastest Path Dialog Box

Selected Approach Offsets Section

Entry Median Offset

Specify the entry median offset value for the selected approach. This is the distance from the splitter island envelope or reference geometry to the fastest path on the entry side.

Entry Edge Offset

Specify the entry edge offset value for the selected approach. This is the distance from the right turn edge to the fastest path centerline on the entry side.

Note: The edge offset is used is for internal calculation only. TORUS generates the transition between arcs using a spline to closely approximate the realistic travel path of a vehicle.

Central Island Offset

Specify the central island offset value for the selected approach. This is the distance from the central island (including the truck apron if applicable) to the fastest path.

Note: All fastest path critical offsets are the minimum offsets from the edge to the fastest path.

Exit Median Offset

Specify the exit median offset for the selected approach. This is the distance from the splitter island envelope or reference geometry to the fastest path on the exit side.

Exit Edge Offset

Specify the exit edge offset value for the selected approach. This is the distance from the right turn edge to the fastest path centerline on the exit side.

Note: The edge offset is used is for internal calculation only. TORUS generates the transition between arcs using a spline to closely approximate the realistic travel path of a vehicle.

Apply to All Approaches

Click this button to apply the displayed offset values to all approaches.

Draw Fastest Turn Path

Select this check box to draw the fastest turn path in the drawing.

Display Friction

Select this check box to add the friction factor to the fastest path data table (separated from the speed values by a colon). The side or lateral friction factor is the coefficient of friction between the vehicle's tires and the road surface. The friction value is assumed to decrease as the speed increases. Values that TORUS uses for the lateral friction factor were determined based on 2004 AASHTO Exhibits 3-11 and 3-12.

Note: The friction values are specified in the Friction.csv file stored in the FrictionData folder located in the user data folder (see Installation -> General Installation Notes: Default User Data Location). Friction.csv is a comma delimited file which can be edited in any text or spreadsheet editor (e.g. Microsoft® Notepad or Microsoft® Excel). The first column refers to the speed in miles per hour, and the second column to the associated friction factor.

Distance

Specify the distance from the inscribed circle diameter to the median offset. By default, TORUS calculates the minimum distance required to obtain each valid fastest path's starting and ending point. Select the Distance check box, and then specify the desired value that is greater than the minimum computed distance in the box. The distance value will not change the calculation of R1, R2, and R3; however, it will provide a smoother transition from the starting point to R1 and from R3 to the ending point.

Note: Since specifying the distance can make TORUS over-constrain the approximation of the fastest through path, it is generally recommended that, for more accurate results, you do not adjust the distance value.

Button	Option	Click to...
	Insert Fastest Path Results Table	Pick a point in the drawing to insert the fastest path results table.
	Export	Export the dynamic fastest path data to a comma separated (.csv) file.

Fastest Path Results Table

TORUS populates the dynamic fastest path results table with the radius and speed data on the approach legs for the fastest paths in the roundabout.

Entry Leg

Displays the name of the entry approach leg.

V1 - V5

Displays the fastest path speed values that ProductName%% calculates for the corresponding travel path radii based on the AASHTO equations in Overview -> Fastest Path.

R1 - R5

Displays the travel path critical radii:

• R1 - the entry path radius, which is the minimum radius on the fastest through path of a vehicle traveling prior to the inscribed circle.
• R2 - the circulatory path radius, which is the minimum radius on the fastest through path of a vehicle traveling around the central island.
• R3 - the exit path radius, which is the minimum radius on the fastest through path of a vehicle traveling into the exit.
• R4 - the radius on the fastest turn path of a vehicle circulating the central island to travel into the approach leg which is adjacent to the entry approach leg.
• R5 - the radius on the fastest turn path to the adjacent approach leg which does not require circulating the central island.

Acceleration

Displays the acceleration value used to calculate V3a, the alternative V3 exit speed. Acceleration is the time rate of increase in velocity with respect to magnitude or direction. To modify the acceleration, use Design Guidelines' Fastest Path Category: Acceleration Rate.

Superelevation

Displays the superelevation values used to calculate the fastest path data. Superelevation is the angle of the road surface. Based on the AASHTO values, the approach leg superelevation is usually assumed to be 2% (+0.02), and the circulatory superelevation -2% (-0.02). To modify the approach leg and/or circulatory superelevation, use Design Guidelines' Fastest Path Category: Superelevation Defaults Section.

Note: Certain columns in the fastest path results table will only display if the related options are turned on in Design Guidelines' Analysis Conditions Category.