The Speed of Light.
On this evening, I set up my tripod over Interstate 5, looking south toward Downtown San Diego. Because of the hazy sky & clouds, we got the beautiful post-sunset pink & purple colors along the horizon.
With a neutral density filter & long 30 second shutter speed, the headlights & taillights of the moving vehicles on Interstate 5 become streaks of light, leading straight to Downtown. Enjoy!