Add and edit yield line to crosswalk sight lines to roundabouts that were created with vehicle envelopes based design guidelines. A yield line to crosswalk sight line determines the area for the driver, when entering the roundabout, to see the downstream exit crosswalk. The yield line to crosswalk distance is measured from the vehicle front positioned before the inscribed circle to the edge of the downstream crosswalk, with an accuracy of equal to or better than 6 inches.

Note:

• The Yield Line to Crosswalk sight line is not available for Turbo Roundabouts.
• If a sight line is red, the yield line to crosswalk distance is insufficient. If the sight lines are green, the yield line to crosswalk distance is sufficient. The cyan portion of the sight line represents the excess distance between the driver’s eye and the crosswalk.

Edit Sight Line - Yield Line to Crosswalk 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 yield line to crosswalk 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 yield line to crosswalk 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