I had stopped at a traffic light in the city and noticed a nail, with date engraved on the head, mounted on a telephone pole. It reminded me of a walk along the tracks near Colebrook that I had taken some time before. On this short walk I had noticed a few ties that had a similar nail in it and the date too was engraved on the heads. These were often used to identify when replacement ties had been placed there, and to identify how old certain ties were.

Whenabouts was the use of these nails discontiued? What is the last railroad to use these nails for identifying tie age?

Thanks in advance.
almo