Between the late 1960s and 2011, the nearby Hawke's Bay Expressway was constructed, providing a high-speed bypass of Napier and Hastings.

[1] This resulted in a confusing driving experience for motorists, made even more so when 9.8 kilometres (6.1 mi) of SH 2 between the northern outskirts of Hastings and the southern terminus of the expressway at Pakipaki was revoked in 2005.

[2] In 2019, an opportunity to renumber the Hawke's Bay state highways arose through the exchange of Meeanee Quay and Pandora Road in Napier (part of SH 2) becoming a local road under the authority of the Napier City Council, and nearby Prebensen Drive becoming a state highway under the authority of the New Zealand Transport Agency.

[3] On 1 August 2019, the renumbering took effect: [4] The creation of SH 51 affected approximately 120 people and businesses with an address change along two sections of the route where the name of the road was the state highway number.

It runs through the small town of Clive and passes to the east of Whakatu before turning towards Hastings at a roundabout at Mangateretere.