Modified Horizontal Head Dallas Display During Lead Left-turn Operation (Using Standard Overlaps)

Approximately 1,000 Dallas displays are currently in operation in the Dallas / Fort Worth area. To convert these Dallas displays to a flashing yellow arrow display with a minimum of hardware and software changes, the solid green lens must be replaced with a yellow arrow lens and the overlap green output used to drive the permissive display must be flashed.  Also, the flash rate should be fast enough to keep the conflict monitor from failing when all overlap outputs are off (600 msec on and 400 msec off).

If standard overlap definitions currently used in the Dallas display are used to drive the flashing yellow arrow display, you will have the flashing yellow arrow displayed simultaneously with the green left turn arrow as shown below. If this is not desired, then the overlap used to drive the permissive indications in the 5-section left-turn display must go dark whenever the green arrow or yellow protected turn arrow is on. This requires additional software in the controller and also requires that the conflict monitor disable Red Monitoring for the channel used to drive the permissive display or for all channels being monitored.

The next two animations show how this additional programming could be used to simulate the Reno Flashing Yellow-arrow Display. However, keep in mind that replacing the solid green indication with a flashing yellow arrow in existing Dallas displays is greatly simplified if you are willing to accept a protected green arrow displayed simultaneously with a flashing yellow arrow.