Evaluates the fastest path for a roundabout that was created with TORUS. The results are calculated and drawn in the roundabout, and can be saved to a file.

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

For an example of how the Evaluate Fastest Path tool works, please play the Evaluate Fastest Path and Fastest Path on User-Drawn Roundabout tutorials (for information on how to play a tutorial, see Tutorials -> Play).

Note:

• 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.
• 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 Evaluate Fastest Path tool is not applicable to roundabouts generated using a German regional design guideline (see Design Guidelines).

Evaluate Fastest Path- Roundabout Dialog Box

Selected Approach Offsets Section

Entry Median Offset

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

Entry Edge Offset

Specify the entry edge offset value. This is the distance from the entry-side right turn edge to the fastest path.

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

Central Island Offset

Specify the central island offset value. This is the distance from the central island to the fastest path centerline.

Note: All fastest path critical offsets are the minimum offsets from the road edge or refined edge (see Refine Edges) to the fastest path.

Exit Median Offset

Specify the exit median offset value. This is the distance from the exit-side splitter island envelope or reference geometry to the fastest path.

Exit Edge Offset

Specify the exit edge offset value. This is the distance from the exit-side right turn edge to the fastest path.

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

Apply to All Approaches

Click this button to apply the currently displayed Approach Offset values to all approaches.

Draw Fastest Turn Path

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

Display Friction

Select this check box to have the friction factor added 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 value. This is measured from the inscribed circle diameter to the median offset. 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: By default, the Distance value is not used, and TORUS calculates the minimum distance required to obtain each valid fastest path's starting and ending point. Specify a value that is greater than the computed minimum distance to have the fastest paths start and end at a desired distance.

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.

Button	Option	Click to...
	Insert Fastest Path Results Table	Place the fastest path results table in the drawing. After you click this button, pick a point in the drawing to specify the location for the fastest path results table.
	Export	Export the fastest path data to a comma separated (.csv) file. The fastest path data (.csv) file opens in your default spreadsheet editor (e.g. Microsoft® Excel). View and/or edit the file, and then close the spreadsheet editor to return to the Evaluate Fastest Path dialog box.