Route 4 is a state highway in Bergen County and Passaic County, New Jersey, United States. The highway stretches 10.83 mi (17.43 km) from Route 20 (McLean Boulevard) in Paterson east to an interchange with Interstate 95, U.S. Route 1/9, U.S. Route 46, and U.S. Route 9W at the George Washington Bridge approach in Fort Lee. The route is a four- to six-lane 40 to 50 mph (64 to 80 km/h) divided highway its entire length, with the portion east of the Route 208 interchange in Fair Lawn a partial freeway consisting of interchanges and right-in/right-out intersections with a few businesses along the road, particularly in Paramus, where the route passes through a major shopping area consisting of numerous malls, Hackensack, Englewood, and Fort Lee. West of Route 208, the route is a surface arterial lined that runs through commercial areas. Route 4 intersects many important roads, including Route 208 in Fair Lawn and the Garden State Parkway and Route 17 in Paramus. The highway is officially named the Mackay Highway,[2] but is rarely referred to as such.

Route 4 was legislated in 1927 to run from Cape May to the George Washington Bridge. This route replaced pre-1927 Route 14 between Cape May and Seaville, what was planned as pre-1927 Route 19 between Seaville and Absecon, pre-1927 Route 4 between Absecon and Lakewood and South Amboy and Rahway, and a spur of pre-1927 Route 7 between Lakewood and Freehold, with the rest of the route to be built on a new alignment. The present-day routing of U.S. Route 9 between Cape May and South Amboy and Route 35 between South Amboy and Rahway bore the Route 4 designation prior to 1953, when the route was defined onto its current alignment. Several spurs of Route 4 existed before 1953 and the Garden State Parkway was originally planned as a bypass of Route 4 that was to be designated Route 4 Parkway. Today's stretch of the route was completed by 1934, not long after the opening of the George Washington Bridge in 1931. It was planned to be upgraded to a full freeway, but plans never materialized. Despite this, the route has seen improvements, such as to the interchanges with Route 17 in 1999 and with Route 208 in 2002.