Add and edit angle of visibility sight lines to roundabouts that were created with vehicle envelopes based design guidelines. An angle of visibility sight line is used to check the angle a driver has to look over their shoulder to see oncoming traffic. The path of the outermost entry lane on the upstream leg is considered to be the most limiting path. The sight line is measured from the driver's eye to the position on the upstream path at the calculated sight distance. The angle of visibility is measured between the sight line and the angle of the first part of the vehicle.

Note:

• The Angle of Visibility sight line is not available for Turbo Roundabouts.

Edit Sight Line - Angle of Visibility Dialog Box

Distance to Yield Line

Specify the distance to yield line value. This is the setback distance from the conceptual yield line (inscribed circle) to the design vehicle when evaluating intersection sight distance.

Critical Gap

Specify the critical gap value. This is the duration of time needed for an entering vehicle to safely enter the roundabout without interfering with upstream or circulating stream vehicles. By default, the Critical Gap value is set to 6.5 s.

Initial Entering Speed

Specify the initial entering speed value. This is the initial speed of the upstream vehicle when evaluating intersection sight distance. By default, the Initial Entering Speed value is set to the R1 velocity of the upstream approach (see Evaluate Fastest Path).

Minimum Entering Sight Distance

Displays the minimum entering sight distance. This is the sight distance calculated based on the entering stream sight distance equation using the Initial Entering Speed value above. TORUS uses the Minimum Entering Sight Distance value to determine the angle of visibility sight line and the obstruction free zone.

Minimum Desired Visibility Angle

Specify the minimum desired visibility angle value. This is an angle measured between the sight line and the angle of the first part of the vehicle. If the Minimum Visibility Angle is less than the Minimum Desired Visibility Angle, the sight line will change its color to the Insufficient Sight Distance color specified in Properties' Sight Lines Category.

Minimum Visibility Angle

Displays the minimum visibility angle value. This is calculated based on the entering stream sight distance equation using the Initial Entering Speed value above and the Critical Gap value above.

Driver's Eye Location Section

Distance from Front

Specify the distance from front value. This is the distance from the front of the design vehicle to the driver's eye

Distance from Driver's Side

Specify the distance from the driver's side value. This is the distance from the driver's side of the design vehicle to the driver's eye.

TORUS calculates the angle of visibility sight line based on the following AASHTO equations:

dEntering Stream = 0.278 (VEntering Stream) (tc)	(metric)
where:	dEntering Stream = sight triangle length, m VEntering Stream = associated speed, km/h tc = critical gap, by default assumed to be 6.5 s

dEntering Stream = 1.468 (VEntering Stream) (tc)	(U.S. customary)
where:	dEntering Stream = sight triangle length, ft VEntering Stream = associated speed, mph tc = critical gap, by default assumed to be 6.5 s