Back when concerns first set in about the Ford Crown Victoria no longer being produced (although they still continue to make them) The Taxi and Limousine Commission started to allow other models in to the taxi mix, such as the Ford Explorer, the Honda Odyssey mini-van, and the Toyota Sienna mini-van. This was before the hype of the hybrid car had started, or before the hybrid car was even in mass-production. Other experiments came and went like the Mercedez E-class diesel, and the Lincoln Town Car.
Each cab has a 3 to 5 year life as a New York City cab before it is forced into retirement. The car purchased to replace the old cab, has to be either an extended Ford Crown Victoria, the wheelchair accessible adaptation of the Toyota Sienna mini-van, possibly the wheelchair version of the Dodge Caravan too but I've only seen the 2007 model, the Volkswagen Jetta diesel, or any of the most popular hybrids except for the Honda Insight. Hence we will soon have no more Ford Explorers, nor will we have any Honda Odysseys, or standard Toyota Siennas.