TORUS 2025 Help
Tools / Evaluate Fastest Path / User-Drawn Roundabout
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    User-Drawn Roundabout
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    Evaluates the fastest path for a user-drawn roundabout. 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).

    Note:

    For an example of how the Evaluate Fastest Path tool is used to generate the fastest path for a user-drawn roundabout, please play the Fastest Path on User-Drawn Roundabout tutorial (for information on how to play a tutorial, see Tutorials' Play).

    To Evaluate the Fastest Through Path for a User-Drawn Roundabout:

    1. Click Evaluate Fastest Path on the TORUS toolbar or ribbon, and then pick a circle element to use as the central island.
    2. Pick a line or an arc reference element in the entry approach leg to use as the entry median.
    3. Pick a line or an arc reference element in an opposing approach leg to use as the exit median.
    4. Pick entry approach leg edge lines/arcs or a polyline.
    5. Pick exit approach leg edge lines/arcs or a polyline. The Evaluate Fastest Path - User-Drawn Roundabout dialog box displays (see below).
    6. Modify the settings in the dialog box as desired.

    To Evaluate the Fastest Turn Path for a User-Drawn Roundabout:

    1. Click Evaluate Fastest Path on the TORUS toolbar or ribbon, and then pick a circle element to use as the central island.
    2. Pick a line or an arc reference element in the entry approach leg to use as the entry median.
    3. Pick a line or an arc reference element in the next downstream approach leg to use as the exit median.
    4. Pick entry approach leg edge lines/arcs or a polyline.
    5. Right-click in the drawing to generate the fastest turn path. The Evaluate Fastest Path - User-Drawn Roundabout dialog box displays (see below).
    6. Modify the settings in the dialog box as desired.

    Evaluate Fastest Path - User-Drawn Roundabout Dialog Box

    User-Drawn Roundabout Elements Section

    Replace the central island, entry median, exit median, entry edge, or exit edge used to generate the fastest path. To replace an element, click X under the element you want to have replaced, click the Replace Selected Element button, and then pick the desired element in the drawing. The fastest path data will be updated accordingly.

    Median Offset Distance Section

    Select this check box to set the Distance and Circulatory Roadway Width values.

    Distance

    Specify the distance from the inscribed circle diameter to the median offset (the fastest paths starting and end points). By default, TORUS calculates the minimum distance required to obtain each valid fastest path's starting and ending point. 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:

    Circulatory Roadway Width

    Specify the width of the circulatory roadway in the roundabout.

    The Circulatory Roadway Width value works in coordination with the Distance value, which is based on the inscribed circle diameter. TORUS does not have information on the inscribed circle diameter of a user-drawn roundabout, so in order to start and end the fastest path at a specified distance, the software calculates the inscribed circle radius by adding the radius of the central island (i.e. the circle element picked in the drawing) to the sum of the Circulatory Roadway Width and Distance values.

    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 edge 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.

    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.

    Leg Superelevation

    Specify the approach leg superelevation value. Based on the AASHTO values, the approach leg superelevation is usually assumed to be 2% (+0.02).

    Circulatory Superelevation

    Specify the circulatory superelevation value. Based on the AASHTO values, the circulatory superelevation is usually assumed to be -2% (-0.02).

    Speed Difference

    Specify the speed difference value. TORUS uses the speed difference to check the speed consistency between the computed fastest path speeds at R1 and R2 on one side and R4 and R5 on the other. Based on the design standards, the default Speed Difference value is set to 20 km/hr and gets converted into the units specified in Program Settings' General Category dialog box.
    Button Option Click to...
    Insert Fastest Path Results Table Have the fastest path results table placed in the drawing. After you click this button, pick a point in the drawing to specify the place for the fastest path results table.

    Fastest Path Results Table

    TORUS populates the 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 ProductNameProductName%% performs the speed consistency check for each approach leg based on the following conditions:

    V1 < V2 + L

    V3 > V1 and V3 > V2

    V5 < V1 and |V5-V4| < L

    where L is the limit of the speed difference. To modify the speed difference limit, use Design Guidelines' Fastest Path Category: Speed Difference.

    R1 - R5

    Displays the travel path critical radii:

    Speed Difference

    Displays the speed difference value.

    Superelevation

    Displays the superelevation values used to calculate the fastest path data (see Leg Superelevation and Circulatory Superelevation).

    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.