Mr I'Anson said four options were carried over from a 2012 report, while the others had since been added according to public feedback.
He said some of the roads would be the same length as the Manawatu Gorge corridor, which is 14km long.
In this instance, there would be no difference to things like road user charges for heavy vehicles, he said.
Each of the alternative routes range from 6km to 19km.
"The one thing we found out while we were surveying was the Tararua Ranges, on the southern side, are about 50 to 80 metres higher than the other - obviously that's a significant factor we have to consider."
He said the options had been based on "very high engineering principles", with most requiring a new bridge to be built.
He wasn't able to give the crowd "too much detail" and encouraged them to visit the project web page to view the alternative options.
"We're now keen to hear from people about the options; what they like about particular alignments, what their concerns might be and any other feedback or suggestions they can provide. Receiving feedback from local people and from stakeholders is a vital part of the ongoing process to find a solution for this route."
He said there would be further opportunity for feedback at two open days to be held in October once the list was shortened.
He said this process usually took up to 18 months and NZTA was working ahead of that, hoping to have a final decision by December.
Ashhurst was also part of the discussion he said, and a long-term option would be to avoid going through the town.
After Mr I'Anson finished, the meeting became heated as attendees demanded to ask public questions.
He initially said questions could be put to individual staff on the floor however, residents were not happy with this.
"How much per annum are we spending on gorge maintenance? Asked one man. "You haven't given us a timeline, you're asking us for solutions.
"I think it's ludicrous."
The Manawatu Gorge options:
• Viaduct: A viaduct through the Manawatu Gorge, along a similar alignment.
• Box Cut Route: A new 6.5km route south of the existing alignment, earth-worked to create a straight alignment from Napier Road (SH3) to SH2/SH3.
• Southern Bank: The opening and upgrading of the existing south bank of the Manawatu Gorge state highway.
• Northern Route 1: A new 15.5km route north of the existing alignment, from Napier Road (SH3) to SH2/SH3.
• Northern Route 2: A new 14km route north of the existing alignment, from Napier Road (SH3) to SH2/SH3.
• Northern Route 3: A new 16.5km route north of the existing alignment, from Napier Road (SH3) south of Ashhurst to SH2/SH3.
• Saddle Road: Upgrade of Saddle Road to improve safety and efficiency.
• Southern Route 1: A new 14km route south of the existing alignment, from Napier Road (SH3) near Fitzherbert E Road (SH57) to SH2/SH3.
• Southern Route 2: A new 14.6km route south of the existing alignment, from Napier Road (SH3) to SH2/SH3.
• Southern Route 3: A new 17km route south of the existing alignment, from Napier Road (SH3) south of Ashhurst to SH2/SH3.
• Southern Route 4: A new 19km route south of the existing alignment, from Napier Road (SH3) south of Te Mata Road to SH2/SH3.
• Long Tunnel: A new 12.7km route, incorporating a 10.5km tunnel from Napier Road (SH3) to SH2/SH3.
• Short Tunnel: A new 14km route from Napier Road (SH3) to SH2/SH3, incorporating a 6km tunnel and re-use of the eastern end of the gorge.
To view these and place feedback, visit www.nzta.govt.nz/projects/sh3-manawatu-gorge
