Regional airlines often require staff to work harder for less pay. This can have a major impact on safety, due to tiredness and cost-cutting. Seven out of the last eight airline crashes in the United States involved regional airlines, and in many of those the National Transportation Safety Board (NTSB) cited tiredness and fatigue as being central to the crash. Regional airlines also have environmental disadvantages, as railways can often provide an environmentally-friendly alternative. For example, travel between the centers of London and Paris is now faster with the Eurostar than by plane.