In 1927, New Jersey's state highways were renumbered. The old system, which had been defined in sequence by the legislature since 1916, was growing badly, as several routes shared the same number, and many unnumbered state highways had been defined. A partial renumbering was proposed in 1926, but instead a total renumbering was done in 1927.

Routes of the original system as laid out in 1927; realignments and additions (whether realized or not) in pink

Some amendments were made in 1929, including the elimination of Route 18N (by merging it into Route 1), and the addition of more spurs, as well as Route 29A, but the system stayed mostly intact until the 1953 renumbering.

A partial renumbering was proposed in 1926 to get rid of the duplicates and assigning numbers to many of the unnumbered routes. The proposed 1926 renumbering would have:

• extended Route 4 over Route 19
• renumbered Route 17N to Route 17
• renumbered Route 18N to Route 18
• renumbered Route 18S to Route 19
• designated Route 21 from Trenton to Buttzville
• renumbered Route 17S to Route 22
• renumbered Route 18 (unsuffixed) to Route 23
• designated Route 24 from Mount Holly to Freehold
• renumbered the Route 20 "from a point on Route No. 3, extending by way of West Berlin, Gibbsboro and Haddonfield, connecting with Haddon Avenue in the Borough of Haddonfield, and continuing to approach the Delaware River Bridge" to Route 25, and extended it from West Berlin to Blue Anchor^{[1] [n 1]}
• designated Route 26 from Five Points to Hammonton
• designated Route 27 from Camden to Atlantic City
• designated Route 28 from South Amboy to Atlantic Highlands
• designated Route 29 from Morristown to Hackettstown
• designated Route 30 from Far Hills to Tri-State

It was eventually determined that an entire overhaul of the numbering system was necessary.

Chapter 319 of the 1927 public laws defined the new system of routes. Major roads received numbers from 1 to 12 and 21 to 50, as follows:

• 1-12: northern New Jersey
• 21-28: radiating from Newark
• 29-37: radiating from Trenton
• 38-47: radiating from Camden
• 48-50: southern New Jersey

Spurs were also defined, being assigned a prefix of S. For example, Route S26 was a short spur of Route 26 connecting to Route 25 south of New Brunswick. A second spur of Route 4 was assigned Route S4A, but two separate spurs of Route 24 both received the Route S24 designation.

While the majority of already-acquired routes were included in the new system, four sections of pre-1927 routes were not. The law authorizing the renumbering indicated that these were to remain, and so the State Highway Commission added a suffix of N to distinguish them from the new routes of the same number:

• Route 4N from pre-1927 Route 4, Eatontown to Belmar
• Route 5N from pre-1927 Route 5, Morris Plains to Denville
• Route 8N from pre-1927 Route 8, Sussex to Unionville, New York
• Route 18N from pre-1927 Route 18N, Fort Lee to Alpine

• U.S. Roads portal
• New Jersey portal
• List of state highways in New Jersey before 1927
• 1953 New Jersey state highway renumbering