When I was in 8th grade, I would peddle my bike from North Cambridge (circa 1963) up to Medford to watch the construction of I-93 north of Riverside Ave (near Medford Sq). Around that time I-93 was first opened from Roosevelt Circle north to NH. The segment from Roosevelt Circle south to Riverside Ave in Medford remained closed until the segment from Riverside Ave to Mystic Ave (just east of Mystic Valley Pkwy) was finished a couple of years later. That Mystic River segment required importation of massive amounts of fill, which I saw hauled in on freight cars on the Medford RR branch. So for about a decade, I-93 ended at Mystic Valley Pkwy, and I-93 traffic dumped onto Mystic Valley Pkwy eastbound toward Wellington Circle. Finally in the early 70s, I-93 was completed thru Somerville to the Central Artery, just barely making it ahead of the expressway moratorium enacted by Gov. Sargent (who, by the way, was a fishing buddy of my uncle George from Gloucester). I also remember riding on the upper deck of the I-93 viaduct in Charlestown (near the Gilmore Bridge) on my bicycle before it was opened in the early 1970s. Fun times.