Add and edit circulatory sight lines to roundabouts that were created with vehicle envelopes based design guidelines. A circulatory sight line determines the area for the driver, when driving around the circulatory path, to see the traffic ahead of them. The circulatory sight distance is measured from the front of the circulating design vehicle. The circle adjacent to the sight line is the sight distance envelope which indicates the area where sight obstructions can be located.

Note:

• The Circulatory sight line is not available for Turbo Roundabouts.

Edit Sight Line - Circulatory Dialog Box

Approach Speed

Specify the approach leg speed value of the design vehicle.

Perception-Brake Time

Specify the perception-brake reaction time value. This is the reaction time between the moment the driver sees an obstacle on the road and the moment they start applying the brakes. By default, the Perception-Brake Time value is set to 2.5 s.

Deceleration

Specify the deceleration rate value. This is the time rate of decrease in velocity with respect to the magnitude or direction. By default, the Deceleration value is set to 11.2 ft/s².

Minimum Sight Distance

Displays the minimum sight distance. This is calculated based on the stopping sight distance equation using the Approach Speed value above. TORUS uses the Minimum Sight Distance value to determine the circulatory sight line and the obstruction free zone.

Toolbox Section

Button	Option	Click to...
	Set Circulatory Sight Line Position	Modify the position of the circulatory sight line. After you click the button, move the circulatory sight line to the desired position, and then click to specify the new position.

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 circulatory sight line based on the following AASHTO equations:

	(metric)
where:	d = stopping sight distance, m t = perception-brake reaction time, assumed to be 2.5 s V = approach speed, km/h a = driver deceleration, by default assumed to be 3.4 m/s2

	(U.S. customary)
where:	d = stopping sight distance, ft t = perception-brake reaction time, assumed to be 2.5 s V = approach speed, mph a = driver deceleration, by default assumed to be 11.2 ft/s2