How noisy does Potrero Hill towards Mariposa and Mississippi get?

I think I found the apartment of my dreams near Mariposa and Mississippi but I'm a bit worried about the noise. The unit's bedroom faces Mariposa directly and is close to the ground floor. About 2 blocks down Mariposa towards the USCF Medical Center/Mission Bay is the gate that comes down at Caltrain goes by - and blares its horn as a warning to cars and pedestrians. I'm also a bit nervous at how busy Mariposa gets since it leads to a freeway onramp.

I've only seen the unit on a weekday at around 6pm, so pretty peak traffic time. Does it quiet down at night? And does the train horn blaring as it goes when the gate is down ever become background noise? Any insight appreciated!