begins at I-495 and US 13 at the southern border of Wilmington and heads north toward the downtown area, where it splits into a one-way pair.

Past downtown, the business route heads through the northeastern part of the city on North Market Street before continuing through suburban Brandywine Hundred on Philadelphia Pike.

The Walnut Street extension south of downtown, which included a new bridge over the Christina River, opened in 1957.

The business route was moved to its current one-way pairing on Walnut and King street in the 1970s.

From here, the business route heads north on four-lane divided South Walnut Street.

heads through commercial areas, becoming undivided as it comes to a bridge over Norfolk Southern Railway's Shellpot Secondary railroad line.

The route splits into a one-way pair, with the northbound direction following South Walnut Street and the southbound direction following South Market Street, with three northbound lanes and four southbound lanes.

The route heads west of Chase Fieldhouse, which is home to the Delaware Blue Coats of the NBA G League.

Immediately after, the business route intersects the eastern terminus of Delaware Route 48 (DE 48), which follows Martin Luther King Jr. Boulevard/Front Street eastbound and 2nd Street westbound, while the northbound direction passes west of the Wilmington Transit Center serving DART First State busses.

Continuing through the downtown, the business route carries three lanes in each direction and runs near high-rise buildings, with southbound US 13 Bus.

widens to four lanes again as it heads out of Wilmington and into suburban Brandywine Hundred, with the name of the road changing to Philadelphia Pike.

The two routes pass suburban homes and businesses, crossing Marsh Road before DE 3 splits from US 13 Bus.

runs along the northwestern edge of the town of Bellefonte before it passes to the southeast of Bellevue State Park.

The business route crosses Stoney Creek as it continues northeast through residential neighborhoods with scattered businesses, heading through Holly Oak and intersecting Silverside Road before it crosses Perkins Run and reaches Claymont.

between DE 9 in Wilmington and US 13 in Claymont is part of the Washington–Rochambeau Revolutionary Route, a National Historic Trail.

[10] The Philadelphia Pike was designated part of a branch of the Lincoln Highway[11] and part of the Capitol Trail in the 1910s, which continued west of Wilmington to Newark and the Maryland border along the present-day DE 2 corridor,[12] then south to Washington, D.C., and Atlanta.

[26] Construction of the Walnut Street Extension, which included the drawbridge, approach roads, and a new bridge under the Pennsylvania Railroad (now Amtrak's Northeast Corridor), was completed in 1957.