Uber just announced it will "aggressively roll out" carpooling, or ridesharing, in the face of increasing competition from startups that offer it as an ultra-cheap transportation option. Uber started as a service for professional taxi and livery drivers, who use the app to find passengers in real time. By contrast, ridesharing essentially lets anyone be a taxi driver: just sign up with an app like Sidecar or Lyft, and anyone with a vehicle and car insurance can start picking up passengers for tips. This practice is potentially illegal across the US; Sidecar is involved in a lawsuit over its legality in Austin.

It seems that the relatively new concept of ridesharing has been nibbling into Uber's business. As a result, the company started experimenting with ridesharing in San Francisco in February. That experiment must have gone well, because now Uber is launching in Seattle and saying it will add ridesharing in any market where regulators have given "tacit" approval — that is to say, expect the notoriously aggressive company to push the envelope anywhere ridesharing hasn't explicitly been banned.

The relatively new concept of ridesharing is nibbling into Uber's business

Uber made the announcement in a 1,300-word document it's calling a "white paper" that addresses the ambiguities in the law and dings "clone companies" Sidecar and Lyft. The company also pledged to introduce "safeguards in terms of safety and insurance that will go above and beyond what local regulatory bodies have in place for commercial transportation."

Ridesharing is part of the trendy collaborative consumption movement which includes companies such as Airbnb and Zipcar. This movement encourages people to rent out their extra space, time, and possessions in peer-to-peer marketplaces. It's a phenomenon that some consider revolutionary, but local laws haven't quite adjusted for how to deal with it yet — Airbnb has gotten some users in hot water for running illegal hotels, for example. That's why Uber did more than simply announce its plans for ridesharing; the company is also making sure to publicly pressure regulators to at least clarify the law.