My first questions would be what kind of roadway are we talking about (speed limit, highway vs. residential, etc.) and why you pulled the vehicle to the side of the road. Obviously, the driver approaching from behind has to do so with reasonable caution. Based on the limited information I believe the driver pulling into opposing traffic definitely has some responsibility. Whether the car pulling over shares in responsibility would probably be based on the circumstances.
Legal questions regarding negligence scenarios can't be digitized neatly into ones and zeros with an absolute yes or no answer. Your presence in the roadway is a condition that would factor into the analysis. Another factor is the driver who came up behind's duty to stay in the roadway and not cross into the oncoming lane unless it can be accomplished with safety.
Actual vehicle locations, measurements as to positions of the vehicles prior to and at the moment of collision, roadway dimensions, vehicle speeds and many other facts would need to be obtained and analyzed in detail before anyone could arrive at a conclusion as to fault.
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I agree with my colleagues. I have an additional comment. You asked two questions. Are you at fault for the accident? Can you be charged with the accident? If by charged you are talking about criminal charges, that would be in the discretion of the police and/or the local District Attorney's Office. If you get a feeling that there's a criminal investigation I would retain a criminal attorney and let him advise you. Also, assuming you have auto insurance make sure you notify your insurance carrier and they will defend you in the civil action.
The bottom line is that it is conceivable that you could be partially liable for this auto accident and could be criminally charged so you should really talk with a good lawyer capable of handling both issues. If you are sued you would most likely be able to get counsel from your insurance company at that time.
But for test
A few circumstances exist where the but for test is complicated, or the test is ineffective. The primary examples are:
Concurrent causes. Where two separate acts of negligence combine to cause an injury to a third party, each actor is liable. For example, a construction worker negligently leaves the cover off a manhole, and a careless driver negligently clips a pedestrian, forcing the pedestrian to fall into the open manhole. Both the construction worker and the careless driver are equally liable for the injury to the pedestrian. This example obeys the but for test. The injury could have been avoided by the elimination of either act of negligence, thus each is a but for cause of the injury.
Sufficient combined causes. Where an injury results from two separate acts of negligence, either of which would have been sufficient to cause the injury, both actors are liable. For example, two campers in different parts of the woods negligently leave their campfires unattended. A forest fire results, but the same amount of property damage would have resulted from either fire. Both campers are equally liable for all damage. A famous case establishing this principle in the United States is Corey v. Havener.
In the United States, the rule of Summers v. Tice holds that where two parties have acted unreasonably, but only one causes an injury to a third party, the burden shifts to the negligent parties to prove that they were not the cause of the injury. In that case, two hunters negligently fired their shotguns in the direction of their guide, and a pellet lodged in his eye. Because it was impossible to tell which hunter fired the shot that caused the injury, the court held both hunters liable.
Market share evidence. Injury or illness is occasioned by a fungible product made by all the manufacturers joined together in a lawsuit. The injury or illness is due to a design hazard, with each having been found to have sold the same type of product in a manner that made it unreasonably dangerous, there is inability to identify the specific manufacturer of the product or products that brought about the Plaintiff’s injury or illness and there are enough of manufacturers of the fungible product joined in the lawsuit, to represent a substantial share of the market. Any damages would then be divided according to the market share ratio.
 Problems with "but for" causation
Since but-for causation is very easy to show and does not assign culpability (but for the rain, you would not have crashed your car – the rain is not morally or legally culpable but still constitutes a cause), there is a second test used to determine if an action is close enough to a harm in a "chain of events" to be a legally culpable cause of the harm. This test is called proximate cause.
There are several competing theories of proximate cause.
The most common test of proximate cause under the American legal system is foreseeability. It determines if the harm resulting from an action was reasonably able to be predicted. The test is used in most cases only in respect to the type of harm. It is foreseeable that throwing a baseball at someone could cause them a blunt-force injury. But proximate cause is still met if a thrown baseball misses the target and knocks a heavy object off a shelf behind them, which causes a blunt-force injury.
This is also known as the "extraordinary in hindsight" rule.
 Direct Causation
Direct causation is a minority test, which addresses only the metaphysical concept of causation. The main thrust of direct causation is that there are no intervening causes between an act and the resulting harm. An intervening cause has several requirements: it must 1) be independent of the original act, 2) be a voluntary human act or an abnormal natural event, and 3) occur in time between the original act and the harm.
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