Part 1; the evolution of Hawaii Route 34 and Maui County Route 341 into Hawaii Route 3400
The Island of Maui seemingly was not part of the original World War II era Hawaii Route System. Circa 1955 the United States Bureau of Public Roads renumbered the Hawaii Route System. The 1955 Hawaii Route Renumbering saw most of the conventions utilized by the current Hawaii State Route System established. Primary Hawaii Routes were given two-digit numbers whereas Secondary Hawaii Routes were given three-digit numbers. The Hawaii Routes were assigned in sequence for what Island/County they were located on coupled with what Federal Aid Program number they were tied to. In the case of the Island of Maui it was assigned numbers in the range of 30-40.
Hawaii Route 34 was aligned from Hawaii Route 32 at Kaahumanu Avenue in Kahului west through Wailuku on a partially completed downtown bypass via lower Main Street and approximately half a mile of Waiale Road. Hawaii Route 34 was connected to Hawaii Route 30 south of downtown Wailuku via non-state-maintained Koa Drive. Maui County Route 341 was aligned north from Hawaii Route 34 at lower Main Street via what is now Waiehu Beach Road and Lower Waiehu Beach Road to Waiehu Beach Park. The original configurations of Hawaii Route 34 and Maui County Route 341 can be seen on the 1955 United States Geological Survey map of Wailuku.
According hawaiihighways.com a 1967 Hawaii Department of Transportation document recommended the removal of Hawaii Route 34 from the Federal-Aid Highway System and by proxy State Highway System. This measure seems to have been taken due to Koa Drive never been taken on as a State maintained facility which meant Hawaii Route 34 never fully functioned as the bypass of downtown Wailuku it was intended to be.
Despite being a mainline State Highway, it appears Hawaii Route 34 may have been always signed with "bypass" placards. A 2001 era image of a Hawaii Route 34 shield along with a bypass placard can be seen on hawaiihighways.com here.
1.5 miles of Maui County Route 341 (Waiehu Beach Road) from lower Main Street to Waiehu Stream and 4.3 miles of Kahekili Highway north of Waiehu Stream were to Camp Maluhia were recommended to be added to the State Highway System. This led to construction of a new connecting branch of Waiehu Beach Road directly to Kahekili Highway. This new construction led to the designation of Hawaii Route 340 which followed Kahului Beach Road (formerly lower Main Street) 1.1 miles, Waiehu Beach Road for 1.5 miles and replacing Hawaii Route 33 over Kahekili Highway for 4.3 miles. Hawaii Route 340 can be seen on the 1983 United States Geological Survey Map of the Wailuku area.
It is unclear when Hawaii Route 3400 replaced Hawaii Route 340 between Kaahumanu Avenue and Kahekili Highway. Hawaii Route 3400 is shown to be interchange with Hawaii Route 340 on the 2017 United State Geological Survey map of the Wailuku area. Hawaii Route 340 shields strangely are occasionally in place along modern Hawaii Route 3400.
Part 2; a drive on Hawaii Route 3400
Hawaii Route 3400 begins via a right-hand turn from the terminus of Maui County Route 330 on Kahekili Highway onto Waiehu Beach Road.
Hawaii Route 3400/Waiehu Beach Road eastbound intersects former Maui County Route 341 at Lower Waiehu Beach Road.
Hawaii Route 3400/Waiehu Beach Road continue east to Kahului Beach Road and lower Main Street. Hawaii Route 3400 makes a left hand turn onto Kahului Beach Road whereas Hawaii Route 34 would have once gone in both directions. For unknown reasons the approach to Kahului Beach Road and lower Main Street is signed "junction Hawaii Route 340."