A delivery truck and a personal car, illegally parked on L Street NW in October. (Bill O’Leary/The Washington Post)

Delivery trucks blamed for clogging Washington streets by double-parking and circling the block soon will be encouraged to make deliveries overnight, when commuter traffic is lighter, and curb space is more available.

Beginning this spring, the District Department of Transportation will test ways to convince businesses to receive deliveries between 7 p.m. and 6 a.m. The city will provide financial incentives that businesses can use to pay higher wages to workers who would receive shipments overnight or reconfigure off-street loading docks to allow unmanned deliveries to areas locked off from the rest of the building. Delivery companies also could apply for the financial incentives.

The test program will target Georgetown, Adams Morgan, downtown, the NoMa area, Capitol Hill and the Golden Triangle business improvement district. Laura Richards, a transportation planner for the District Department of Transportation (DDOT), said more overnight deliveries should reduce traffic congestion, improve the flow of freight into and out of the city, and reduce truck emissions.

“People can look forward to fewer trucks on the road during peak hours,” Richards said.

She said the biggest challenge will be convincing businesses to try something new. Many owners resist the idea because they don’t want deliveries made when they’re not there, Richards said. The city’s pitch: Overnight deliveries would make their shipments more reliable and could allow some to reduce the extra inventory they keep on hand to cover for late or missed deliveries.

The 3 1/2-year pilot program will be funded through a $150,000 grant from the Federal Highway Administration and $150,000 from DDOT, Richards said.

DDOT estimates the annual cost of truck-related traffic congestion at $650 million, and it’s projected to get worse. Between 2011 and 2040, truck volumes in the city are expected to grow by 70 percent for inbound traffic and 137 percent for outbound traffic.

A similar 2010 pil0t project in New York City led to a longer-term off-hours delivery program, Richards said.

This is the District’s latest attempt to reduce traffic congestion from delivery trucks. Starting in January, the city required trucks parked in commercial loading zones to have a $323 annual decal. The loading zones were previously free. Commercial trucks with the decal also were allowed to use metered spaces for free during the mid-day. Trucks parked in loading zones without a decal risk a $100 ticket, and fines for regular vehicles parked in commercial loading zones doubled to $100.