These lines were very common in Boston and some stretches still exist but with fewer conductors. The majority employed side-tie composition pintype insulators (as you see here) to support the heavy copper wire. Why the transit authority opted for the side-tie method instead of using saddle-groove insulators, I'll never know. In some locations CD 140 "Jumbo" insulators were used along streets for trolley service as well. The existing routes either have side-tie composition or modern porcelain cable tops for supporting the city's trolley power lines. The CD 140s were upon lines taken out of service many decades ago. None have been found by collectors.