create multiple entries in attribute table

I have a road feature class with about 4,500 segments for a study area. I need to designate them as "open" or "closed" to the public with open=1 and closed=0. I am eliminating the low hanging fruit and selecting large portions that are clearly open and entering a "1" into the field.

I am trying to find a way to enter the "1" into a column in bulk, as opposed to manually entering it thousands of times. Any tips?

Thank you.