During morning rush hour, light on Mass Ave SB turns red at Wisconsin before it turns red at Cathedral. As a result, the stretch of Mass Ave between Cathedral and Wisconsin fills with cars, which prevents right turns from Cathedral EB to Mass Ave, resulting in large backups on Cathedral EB.

Comments update: 14-00299761-Traffic Signals Investigation
3700 Massachusetts Avenue Northwest, Washington, DC 20016, USA
Signal on Mass Ave Nw SB at Wisconsin turns red before signal at Cathedral, causing gridlock
By DINKINS, ANTHONY: 2/19/2015 3:16:20 PM
The request will be further reviewed. The operation currently is working according to design. Thanks.