General Motors aims to build as many as 500,000 vehicles that utilize some sort of electric technology by 2017. Speaking to reporters this week, GM’s product development chief, Mary Barra, said the company’s fleet of cleaner vehicles will include the plug-in Chevrolet Volt; the all-electric Spark EV, which will go on sale in some markets next year; and cars that utilize the eAssist technologies, which can improve efficiency in some vehicles by as much as 25 percent. A half-million vehicles would represent about 5 percent of the company’s global sales last year; GM expects to sell 50,000 vehicles equipped with electric technologies this year. While the market for electric cars is sluggish, Barra said plug-in vehicles remain central to the company’s strategy. “We have every intention of maintaining our leadership position in plug-in vehicles,” she said. Like all automakers, GM will need to offer more fuel-efficient vehicles to meet stricter U.S. auto emissions standards that will be in place in 2025.