Bridge City Hustle

My phone is buzzing and I wonder who would be writing me a text message at 6pm on Sunday night. It is Bill, excited that it stopped raining after few straight days of downpour here in San Francisco. 45 minutes later, I am running with a hot pizza in one hand and tripod in another, jumping in my car and heading out to pick up Bill.
Five more minutes later, we are on the island. Yerba Buena Island that is. It is not as romantic as it sounds though. Yerba Buena Island is a cold place halfway between San Francisco and Oakland. A tunnel runs straight through it. The tunnel is part of the San Francisco Bay Bride, that has two parts. The more famous half of the bridge spans between the island and San Francisco. The second part connects the island and Oakland.
Here is a behind-the-scenes photo of the location we settled at:
The narrow windy road at the top of the island was covered with broken branches and leaves after a couple of recent storms. The only people we saw were other photographers, easily recognizable by their tripods. We found a couple of holes in a fence and shot the less known part of the bridge (towards Oakland).
Here is the result of our night adventure... a photo of an old bridge, side by side with the construction site. You can clearly see the two levels of the bridge and their direction if you pay attention to the color of car lights. Yes, the red lights are heading towards Oakland. The construction on the left continues, and I can't wait to drive through this brand new steel and concrete bridge one day.
This last shot is taken at the same spot I photographed Meena and Evan. While shooting, I observed that the cars were coming out of the tunnel in waves. Can anyone explain why? They get in through a toll station and there is no traffic light to cause the "heartbeat".