The new track would run along an already formed trail from Colombo Rd to Colin Pugh Sports Bowl, and then go under the Opaki bridge, behind Mawley Park and up to the proposed bridge near the railway line.
"The main point to the bridge is to make a loop trail so people can get off the train and go straight on the trail, and people down at Henley Lake can access the loop at the Colombo Rd end," Mr Irwin said.
"At the moment some people are walking over the rail bridge from Lincoln Rd or Oxford St to get to the other side. If there's a bridge, they'll be able to use that.
"It will be convenient for them to catch the Wellington train, and make it easier for some to access town."
There are two options as to where the bridge could go.
Mr Irwin said placing it west of the railway bridge was more desirable, regarding cost and position.
"The banks are high either side and it's not too wide -- so cheaper construction."
However, there is some uncertainty regarding the Greater Wellington Regional Council's 1-in-100-year Floodplain Management Plan, so another site on the east side of the railway bridge is being investigated.
The bridge could cost up to $200,000.
At 71, Mr Irwin, a former surgeon, is a keen cyclist.
"I love the freedom the bike gives you, it's really good for exercise and for health and I would encourage everybody to think about getting on a bike."
He said the loop trail would benefit cyclists who were not confident riding on the road.
"We want people feeling safe and empowered to use their bikes."
Mr Irwin said the trust was strongly in support of Bikes in Schools, a national programme introduced to schools that enables students to ride bikes at school on a regular basis.
"They have found that Bikes in Schools has raised the children's fitness, confidence and it has decreased the obesity rate."
In December Mr Irwin presented the Waipoua River bridge proposal to a GWRC environment subcommittee, which indicated its support for the project and noted that it was unlikely to conflict with the Floodplain Management Plan.
Mr Irwin plans to approach the Masterton District Council with the proposal.