How to calculate width and lengths of street layer in Postgis/PostgreSQL?

I was able to project the point location (ad.shp) to the nearest street (line.shp) like this.

My approach was like this. I used ST_ClosestPoint() to iterate this for every point location within a distance of 10 meters and it worked well! (Yes, suggestions for improvements are always welcome).

    Select  ST_ClosestPoint(line, pt) As closest_pt_line
From
    (Select ad.geom As pt,
        st.geom As line,
        ST_Distance(ad.geom, st.geom) As d
    From ad, st
    Where ST_DWithin(st.geom, ad.geom, 10.0)
    Order By d
    ) As foo;

Based on this interpolated point at street layer I want to calculate the width and length of street in both direction. The scenario can be visualized as follows:

The length of street needs to be calculated in both direction based on the interpolated point and street width needs to be calculated with reference to building polygons. I am aware of ST_Length() in Postgis but it returned the length of whole linestring rather than length 1 and length 2 (as shown in figure). Any advice for how to calculate street lengths and width in PostGIS?