Intelligent car door clamps up when danger’s about Accidents caused by car doors being opened into the path of oncoming vehicles or cyclists are common in cities. But these incidents could become a thing of the past, if doors that react to potential impacts catch on. The creative idea of Michael Graf at BMW and Michael Strolz’s team at the Technical University of Munich, the "haptic"-technology that gives tactile feedback-doors could cut both road injuries and repair bills, they say. The current prototype looks like a normal car door, but an extra metal bar runs through its centre and connects to the car’s frame between the hinges. In normal mode, the bar moves freely and doesn’t affect the door’s movement. However, if sensors detect a nearby obstacle at the same time as an accelerometer detects an attempt to open the door, the door’s swing is restricted by a linear motor attached to the bar. To pass on more information to the user, the amount of door resistance is in proportion to the proximity of an object-for example, you might swing a door halfway open without problems before it gets stiffer as it nears a lamp post. The current prototype uses supersonic sensors to spot dangers, but because they have a limited field of view, the next version will use cameras that can span 180°, says Strolz. "Then we will be able to sense the complete workspace of the door and detect people walking by the car or cycling towards it," he says. Reactions from 16 volunteers who tried the new door at BMW’s Munich research centre have been encouraging, the team told a recent conference on haptics in Salt Lake City, Utah. The technology is mature enough that a car factory could be pumping it out in cars within a year, says Strolz. The basic mechanism is like one already featured in some cars-for example, taxis with automatic passenger doors. However, BMW is yet to make any decision on whether to roll it out. What stage has the new technology reached according to Strolz

A. It is mature enough to be put to manufacture within a year.
B. It is still at the starting point and no actual use is possible.
C. It has already been used on some cars.
D. It has been approved effective by authorities.