which authority is in charge of maintaining it?
The New York State Department of Transportation.
New York State Route 146
In 2007, the New York State Department of Transportation (NYSDOT) has identified the NY 146 corridor from Riverview Road to Glen Ridge Road as in need of future improvements. 
which places are connected by new york state route 146? Gallupville, Mechanicville and Schenectady. which counties does it pass through? Schoharie County. when was it designated as route 146? 1930 was it known by any other name earlier? UNANSWERABLE
wiki:23139970
New York State Route 146 [SEP] History
In 2007, the New York State Department of Transportation (NYSDOT) has identified the NY 146 corridor from Riverview Road to Glen Ridge Road as in need of future improvements. Intersection improvements are scheduled at the NY 146 / Aqueduct Road / Williams Road and NY 146 / Riverview Road intersections. This part of the project will be built in 2008 and is to include new turn lanes at each intersection. To the south, the Rexford Bridge over the Mohawk River and the surrounding roadway will be improved in stages, with completion expected by 2017. The objective of these projects is to improve highway capacity and safety along the corridor.