Short answer: the door zone is the strip beside a parked car where an opening door can hit a rider. The Active Transportation Alliance puts it at "the 4-foot area along the side of a parked car" and advises riding at least 4 feet from parked cars. The League of American Bicyclists says to ride outside the door zone when passing parked cars, even if that means riding outside the bike lane. When there is not enough room for that and a safe gap from passing traffic, the League's answer is to take the lane.
If parked cars scare you more than moving ones, that reaction is not irrational. A door can open with no warning, there is rarely anywhere to go, and the person opening it is usually not looking for you.
What the Door Zone Is, and How Big It Is
A door zone is the space a car door sweeps through as it opens. Nothing about it is marked on the road, which is part of the problem: you have to judge it every time you pass a parked car.
The Active Transportation Alliance, a Chicago-area advocacy group, describes it in its guide to avoiding the door zone: "The Door Zone is the 4-foot area along the side of a parked car where an opening door can hit and seriously injure a cyclist." Its advice for riding in a bike lane beside parked cars is to "ride on the left side of the lane, at least 4 feet from parked cars."
Four feet is a working figure, not a legal one. Doors vary in length from car to car, so treat it as the minimum to aim for rather than a precise boundary.
Why a Bike Lane Does Not Always Keep You Out of It
Many riders assume a painted bike lane beside parked cars is the safe place to be. A study reported by Streetsblog Chicago suggests the opposite can be true. The Transportation Research Board study, which observed thousands of riders in Chicago and Cambridge, Massachusetts, tested bike lanes 4, 5 and 6 feet wide next to parked cars. Its findings, as reported:
- Riders tended to ride in the center of the lane regardless of its width, which put them within door-swing range, described as a four-foot radius.
- On one Chicago street, "few bicyclists rode outside the door zone when the bike lane had no buffer, then after a two-foot buffer was striped, 40 percent rode outside the door zone."
- The researchers concluded that "a six-foot-wide bike lane offers no advantage over one that's five feet wide, or even four feet wide," and recommended a narrower lane with a buffer on the parking side.
The practical lesson is that the paint is not the safe line. A lane can look generous and still place you where a door opens. Where the marked lane runs into the door zone, the League is explicit that riders should be "far enough to the left to avoid a suddenly opened door, even if it's outside the bike lane."
That advice only works if you are allowed to leave the lane. Whether you may leave a bike lane differs by state and city, and some places require riders to use a bike lane where one exists, with exceptions for hazards. Check your own vehicle code and your city's rules.
Three Common Street Layouts, and What the Sources Say About Each
The right position depends on what the street gives you. This table summarizes the sources above. It is not a rulebook, and local conditions change the answer.
| Layout beside parked cars | What the sources say | What it means for your line |
|---|---|---|
| Bike lane with no buffer | In the reported study, few riders rode outside the door zone on a Chicago street with no buffer | The lane's center may be inside door range, so the guidance points to the left side of the lane or beyond it |
| Bike lane with a parking-side buffer | After a two-foot buffer was striped on that street, 40 percent rode outside the door zone | The buffer gave riders a visible cue to stay clear of the doors |
| No bike lane, a travel lane beside parked cars | The League says to ride outside the door zone and to take the lane when there is not enough room to share | A line at least 4 feet from the cars, which may put you well into the lane |
How Common Is Dooring?
Counts vary by city and by how crashes are reported, so no single national figure is quoted here. One local data point: the Streetsblog Chicago report says that in Chicago "18 percent of reported bike crashes were doorings" in 2012, the most recent year available at the time of its 2014 publication. That is one city and an old year, and it only counts crashes that were reported. It shows that dooring can be a large share of a city's reported bike crashes, not what your street looks like today.
What the Law Asks of the Person in the Car
Door-opening rules are state law. California's Vehicle Code 22517 says: "No person shall open the door of a vehicle on the side available to moving traffic unless it is reasonably safe to do so and can be done without interfering with the movement of such traffic." Other states have their own versions, and some cities add penalties.
Knowing that the law is on your side is useful afterward, but it does not stop the door. A legal duty on the person opening the door is not a reason to ride within reach of one.
Last verified: October 3, 2026, for the California statute quoted. Check your own state and city.
How to Ride Past Parked Cars
These steps combine the League's and the Active Transportation Alliance's guidance:
- Pick a line outside the door zone before you reach the cars. Aim for at least 4 feet from the parked cars. Beside a row of parked cars, that can mean the left edge of a bike lane or a position well into the travel lane.
- Look inside the cars as you approach. The Active Transportation Alliance advises checking inside parked vehicles before passing. A car with someone in the driver's seat, brake lights on or a person getting out is the one to give extra room.
- Know what is behind you. You may need to move left to clear the door zone, so you need to know whether a vehicle is about to pass. The Alliance advises watching traffic behind you and being "prepared to move to the center of the lane" if needed to keep a safe distance from passing motorists.
- If there is not enough room for both, take the lane. The League's guidance is to take the lane when "there is not enough room to share the lane." Many riders feel they must choose between the door zone and a close pass. Riding in the lane is the third option, and it is the one the League describes for this situation.
- Stay predictable. Move to your new line early and hold it, rather than weaving in and out around each parked car.
When the Door Zone Gets Worse
A few conditions make the door zone a bigger problem, and each has a seasonal or practical link:
- Poor light. At dusk and after dark, it is harder to see into parked cars and spot a person about to get out. Our fall cycling tips cover what changes when the evening commute starts in the dark.
- Wet roads. If you have to stop fast for a door, wet pavement lengthens stopping distance. Our guide to bike braking in the wet explains what changes.
- Leaves and debris along the curb. Wet leaves are slippery enough to matter when you are choosing a line beside parked cars. See our guide to riding on wet leaves.
- Busy curbs with stops and drop-offs. Streets with frequent stopping, such as near schools, shops and transit, mean doors open more often.
What to Do If You Are Hit by a Door
This guide cannot replace professional advice. If you are hit by a door, have any injury checked by a medical professional. For questions about who is responsible and what your state's rules provide, a local attorney or your state's bicycle advocacy group can explain the rules where you live.
FAQ
How far should I ride from parked cars on a bike?
The Active Transportation Alliance advises at least 4 feet from parked cars and describes the door zone as a 4-foot area. The League of American Bicyclists says to ride outside the door zone even if that means riding outside the bike lane. Doors vary in size, so four feet is a minimum to aim for, not an exact boundary.
Is the bike lane next to parked cars safe from doors?
Not necessarily. A study reported by Streetsblog Chicago found that riders tended to ride in the center of the lane, within door-swing range, whatever its width, and that a two-foot buffer on the parking side led more riders to stay outside the door zone. A lane without a buffer can place a rider within reach of an opening door.
What should I do if there is no room to avoid the door zone and stay clear of cars?
The League's guidance is to take the lane when there is not enough room to share it. Check your state and local rules on leaving a bike lane, because some places require riders to use one with exceptions.
Is it illegal to open a car door into a cyclist?
In California, Vehicle Code 22517 says no person shall open a vehicle door on the side available to moving traffic unless it is reasonably safe and does not interfere with that traffic. Other states have their own laws, and local penalties vary.
Does the door zone only matter on the right side of the road?
No. The door zone applies to any parked car you pass, on either side of a street. On a one-way street with parking on the left, doors on the left side deserve the same attention.
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