Along with my 30 mile route to Needham, this ride up to Lexington is one of my standard quick rides to get in when I only have a few hours free. It again leaves from downtown Boston and heads out Beacon Street. This time though, you take a right onto Chestnut Hill Ave at the reservoir to get over onto Commonwealth. Comm Ave then takes you through Newton and finally across the Charles River. There is a carriageway here which allows you to avoid traffic if particularly heavy,
Comm ave is mostly a warm-up though, once you cross the Charles and then I-95 the roads get quieter and prettier. There is a short but steep climb up Newton Street past Pine Brook Country club then things settle out through Weston and up Tower Road into Lincoln. Coming out of the stop sign in Lincoln there is another steep section, made more painful by the fact that you have no momentum after wating at the 5-way intersection. From there you descend into Minuteman State park and then cut back across just south of Lexington center (or take a detour up Waltham street to Mass Ave to pick up a coffee at Ride Studio Cafe). Once into Arlington the best way to avoid traffic is to catch the Minuteman bikeway, but the entrance can be a bit tough to spot off Maple street. The key is to watch for when you pass over it, then look for an entrance ramp just off to the right.
I used to just pick up Mass Ave once the bikeway ends in Arlington Center, but that was a constant frustration of traffic lights, cars parked in the bike lane, and potholes. I find it actually it much nicer to cut over to Broadway instead then to Elm St through Davis Square into Porter and then onto Beacon/Hampshire back to MIT before finally crossing the Mass Ave bridge back to Boston.
Total route is 40 miles and for much of it, you really feel like you’ve gotten out of Boston.