A factor limiting natural-gas-powered sales is the arrival of new, more efficient diesel engines. Pictured, a trucking firm’s fuel pump in Florida. Edward Linsmier for The Wall Street Journal In the midst of the strongest market for commercial trucks in eight years, North American sales of natural-gas-powered haulers are just crawling along. Higher purchase prices compared with diesel trucks, improved diesel fuel economy and continued scarcity of fueling stations are damping natural-gas-powered truck demand. About 10,480 of the heavy-duty trucks are expected to be sold this year, up 20% from the 8,730 sold last year, according to Power Systems Research. However, some forecasters had expected sales to about double to 16,000 vehicles this year amid the trucking industry’s enthusiasm for natural gas a year ago. What happened? A big roadblock remains the premium for a heavy-duty gas truck—$50,000 more than the about $150,000 for a new diesel-powered truck. In […]