As part of a global, company-wide initiative, DHL Express has replaced approximately 75 percent of its 3,100-vehicle U.S. fleet with new, more fuel-efficient vehicles in 2014 and 2015, and over half of the vehicles it's adding in 2015 run on alternative fuels, the parcel delivery company announced.

The company has expanded its propane autogas vehicles in Detroit, Chicago, and Elizabeth, N.J., and introduced new battery-electric vehicles in New York and San Francisco. Additionally, DHL will be testing new gasoline hybrid-electric vehicles in several locations.

Under its GoGreen initiative, DHL looks to add fuel-efficient, hybrid, electric, or aerodynamically modified vehicles to its fleet worldwide. In addition, by the year 2020, DHL aims to improve the carbon efficiency of its operations by 30 percent compared to 2007, according to the company.

Having invested nearly $50 million in new U.S. fleet vehicles over the last two years, DHL has reduced its average fleet vehicle age from 6.7 years in 2012 to the current 3.6 years.

DHL's U.S. fleet includes over 500 propane autogas vehicles, 92 battery-electric vehicles, 54 hybrid-electric vehicles, 425 clean diesel vehicles, and 70 high-efficiency compact delivery vehicles.