When they consider the best ways to deliver large parcels on narrow streets, logistics and transportation companies have limited options. Big trucks can't fit around corners or squeeze through narrow lanes, while couriers on foot have a limited range.

UPS thinks it has found a perfect compromise. The company is now expanding a pilot program that uses bicycles boosted by electric motors to navigate the winding lanes of Europe's congested cities.

The transportation and logistics giant has begun testing battery-aided cargo bikes for package delivery in downtown Basel, Switzerland, after achieving success with a similar program in Hamburg, Germany.

The vehicles, which have a load capacity of two cubic yards and a cargo weight limit of 330 pounds, measure just three feet wide—ideal for handling the heavy traffic and tight turns demanded for city-center delivery.

To help its drivers balance the weight, UPS added a third wheel on the rear axle. When empty, the cargo tricycles weigh just 250 pounds, including the 250-watt battery.

If the concept catches on, the program could have both economic and ecological benefits, such as reducing inner-city congestion, noise, and carbon dioxide emissions. The new delivery vehicles also have the potential to streamline UPS's urban delivery operations by trimming the time spent searching for parking spots, the company said.