This is about bike shares and the author states:

If you’re cruising along on a road bike at 20 mph, hit a rock, and get thrown forward onto your head, you definitely want a good helmet to absorb the blow. Studies have shown that wearing helmets while cycling reduces the risk of head and brain injuries by about 70 percent, and regular bike commuters should make the decision to wear a helmet, no question. Helmet law proponents argue that these benefits would carry over to bike-share riders, but in fact, the safety picture is more complicated.

Do we need to require that you carry your helmet all day in case you decide to hop on a clunky 40-pound bike-share cruiser to go two blocks from office to lunch? The risk of severe injuries on these short jaunts is low, and in the rare cases where riders are killed, it is most often in devastating collisions with cars and trucks where, as New York City Council Speaker Corey Johnson bluntly put it, “a helmet wouldn’t even help them because of the sheer scope of the accident.” The biggest threat to city cyclists is motor vehicles who don’t see them and don’t respect their space on the road and wearing a helmet is unlikely to mitigate the danger of these bike vs car collisions.