Add and edit approach to yield line sight lines to roundabouts that were created with vehicle envelopes based design guidelines. An approach to yield line sight line determines the areas along the side of the road where objects should not be placed so the driver can see the intersection. The approach to yield line distance is measured from the vehicle front to the point where the path of the vehicle intersects the inscribed circle diameter with an accuracy of equal to or better than 6 inches.

Note: Approach to yield line sight line is equivalent to Criterion 1 sight line in Australian guidelines.

Edit Sight Line - Approach to Yield Line 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 approach to yield line sight line and the obstruction free zone.

Sight Distance Type Section

Line of Sight / Stopping Sight Distance

Select how the minimum sight distance should be measured:

• Line of Sight is a straight line representing the sight of the driver. The line of sight is calculated based on a stopping sight distance equation and is measured from the driver's eye to the point of interest (e.g. to the crosswalk).
• Stopping Sight Distance is the distance required for a vehicle to completely stop from its initial speed, including the distance traveled within the perception-brake time.

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 approach to yield line 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