It was the "ultra-fast broadband of its day" in terms of providing an economic and social boost to Whanganui and Ruapehu districts.
When the Parapara Rd opened in 1917 it slashed the travel time between Whanganui and Raetihi in half - from nine hours to about four.
Today the journey takes about 75 minutes. The centenary of the Parapara will be celebrated tomorrow when a convoy of 23 vintage cars and 20 motorcycles led by mayor Hamish McDouall in a Morris Minor 1000 make the trip.
The delegation will leave from St Hill St in Whanganui at 8.30am and head past the River Traders' Market before making its way up the Parapara.
There will be a morning tea break at Raukawa, where the group will be joined by the Norton Owners' Club before arriving in Raetihi at 11am.
Official celebrations will start there at 10am with the museum and food stalls open, followed by an address from both Mr McDouall and Ruapehu mayor Don Cameron, and the cutting of the centennial cake.
Whanganui and Partners' Louise Follett said the celebration was about the economic and social benefits created by the Parapara Rd.
"It was massive for the farmers who operated in the area, and it was the route that got us north and saved us a huge amount of time," she said.
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"Roads and rail were the ultrafast broadband of the day. From a Whanganui and Partners perspective, it's about relationships with our neighbours and about getting people to connect with each other and create opportunities."
Gallery: The end of the road: After the June 2015 floods the Parapara was closed due to slipping about 200m north of Te Rimu Road turn off.
A Chronicle report on that first trip over the Parapara from March, 1917 reveals a much more arduous journey than today. "In view of the fact that some streams have not yet been bridged and that a good long section of the road remains unmetalled, the undertaking was a rather severe test for the car," the paper wrote.
The first trip, in a Studebaker, took 41/2 hours, which, in those days, was half the the nine hours it took on the "very tiresome travelling" and "very roundabout route up the Main Trunk".
"This is really splendid, and farmers and residents of the Raetihi and Wanganui districts respectively can look forward to the near future when the Parapara Rd will be the means of affording regular daily communication between the two towns," the paper reported.