While it is certainly true that the general rule in New York is that one driver who rear-ends another is presumed to be at fault for the accident - and may ultimately wind up with an award of summary judgment against him, there are some important exceptions to this general rule. In other words, this presumption is not automatic; it is rebuttable.
Two of these exceptions, which were recognized in two separate decisions from New York's appellate courts, are as follows:
(1) where the driver of the vehicle that was rear-ended failed to remove his vehicle from the roadway; or,
(2) to warn oncoming traffic that his vehicle was disabled.
There is an important caveat to these exceptions, however: both of them inherently assume that the driver of the moving (and rear-ending) vehicle is able to demonstrate via competent proof in admissible form that the non-moving vehicle's purported negligence was a substantial factor in causing the accident. In other words, absent proof (i.e., not mere speculation) that the accident would likely not have occurred but for the driver of the non-moving vehicle's purported negligence, any errors by the driver of the stopped vehicle will be disregarded, and will be insufficient to rebut the rear-ending driver's presumption of negligence.
Thus, for example, if the driver of the moving car was speeding, or following too closely, the driver of the front vehicle's failure to have working brake lights or failure to remove his vehicle from the roadway may very well be deemed irrelevant, because even had they been working, the outcome of this accident probably would have been the same either way.