Distinguishing characteristic of this bridge is the word "Lackawanna" spread out over only 3 bridge panels.

According to catalogs, the various color versions were sold in the following years, but this is not completely accurate.

Red - 1939 and 1940
Black - 1941 and 1946
Silver - 1948, 1949, and 1950

According to the Charles Sommer guide, the 1947 version was also silver and the black bridge was offered from 1940-1942.  While a bridge was illustrated in the 1946 catalog, actual production of HO trains did not begin until 1947.  This bridge does not appear to have been cataloged in 1947

Note:  Catalog illustrations are not accurate.   It appears that photos of the S gauge 581 bridge were used on numerous occasions.  That bridge has only 7 full panels as opposed to 11 full panels on the HO bridge.   See the upper catalog illustration on this page as an example.