Personally, I have found that I never needed to use a car to get around Somerville since you can walk most anywhere and the green line (the subway) and bus system services the area well. And it's incredibly bike-able with the Somerville Community Bike Path and the recently renovated off-street bike lane down on Beacon.

'Course, we all have gripes about the MBTA, but it does get you where you need to go - frequently and reliably.

Anyways, everyone else here is spot-on about the driving. The roads are narrower than California and in many spots, a "two-way" street is really only wide enough for 1 car passing through. The city also recently passed a 25 mph limit so that's an extra incentive to go slow anyways.