Why do some freeway ramps have an extra red light?


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Additional reading:
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“Ramp Metering: A Proven, Cost-Effective Operational Strategy—A Primer,” Federal Highway Administration
https://ops.fhwa.dot.gov/publications/fhwahop14020/sec1.htm

“Ramp Meters,” Wikipedia
https://en.wikipedia.org/wiki/Ramp_meter

“Cost Estimates for ITS Devices of the T-REX Project” Summary, US Dept. of Transportation, 11/2001
https://www.itskrs.its.dot.gov/its/benecost.nsf/ID/278509cbe71f063f85256db100458931?OpenDocument&Query=CApp

“The Minimum Yellow Timing for Ramp Meters,” Wang, Liu
https://www.sciencedirect.com/science/article/pii/S2046043016301009

“Case Studies of U.S. Freeway-to-Freeway Ramp and Mainline Metering and Suggested Policies for Washington State,” Jacobson, Landsman
http://onlinepubs.trb.org/Onlinepubs/trr/1994/1446/1446-008.pdf

“A Case for Freeway Mainline Metering,” Habobian
http://onlinepubs.trb.org/Onlinepubs/trr/1995/1494/1494-002.pdf