Don't Get the Door Prize
One of the most under-appreciated dangers that bicyclists face is a suddenly opening door of a parked car.  These collisions can be very serious. However, there is a simple solution: never ride within a door's width of a parked car. If you could touch the car you are definitely too close.

Always ride a door's width away from parked cars. In Jamaica Plain, this leaves you barely enough room to stay away from trolley tracks.

Beginner bicyclists like to stay out of the way of traffic, and sooner or later they will win the door prize. Even experienced riders often ride too close to parked cars in urban Massachusetts because riding further out would prevent motorists from overtaking without changing lanes. Don't let other's impatience make you ride dangerously! Although motorists may tell you to get off the road, the risk that a driver or passenger of a parked car will open a door in your face is much greater than the risk of a driver deliberately running you over. If they honk at you, they see you. 

It would be a good thing if someday all main streets with on-street parking in the Boston area had wider curb lanes or wider parking lanes (or both) so that cyclists could ride safely and not enrage ignorant motorists.  Changing the standard width of a parking lane from 7 or 8 feet to 10 to 12 feet would help this (see roads in the program section).

If there are only one or two cars on the block, and you can see that they empty, it's safe to ride next to them.  But on most urban streets there are too many cars to check all of them, and you don't want to swerve away from a car that you think is risky at the last minute, possibly into overtaking traffic.

This cyclist rides out of the reach of parked car doors and still leaves enough room for motorists to overtake without crossing the lane line. But always stay out of the door zone, even if motorists cannot pass in the same lane. It's your job to avoid potential obstacles on the side of the road. Graphic copyright State of Oregon.

Riding in Traffic
Traffic Basics
Obey Your Signals
Don't Get Doored
Road Hazards
Make It Turn Green
Stay Away from Trucks
Use Lights at Night