A project to improve cycle paths in south Wales as part of a UK-wide scheme is one of four bidding to receive £50m from the Big Lottery Fund.
The Treforest bridge would link university campuses with residential areas
Voting lines have opened to decide which scheme will get the money.
If successful, the bid by sustainable charity Sustrans for its UK-wide cycle paths project could see cycle bridges being built in Cardiff and Treforest.
It will need to beat rival bids from the Eden Project, Sherwood forest and the Black Country Urban Park.
The winning bid will be announced on ITV1 on Wednesday.
Sustrans' bid is for its Connect2 project which aims to create new walking and cycling routes in 79 cities across the UK.
It aims to build new bridges and crossings over busy roads, railways and rivers which currently stop people getting about by foot or on a bicycle.
In Cardiff the proposed cycle and footbridge over the River Ely would improve access for commuters, residents and tourists travelling between Cardiff and Penarth, said Sustrans.
TELEPHONE VOTING NUMBERS
Eden Project: The Edge - 0870 24 24 601
Sustrans - Connect2 - 0870 24 24 602
Sherwood: The Living Legend - 0870 24 24 603
Black Country Urban Park - 0870 24 24 604
The link will also provide a sustainable transport route to and from the International Sports Village in Cardiff Bay.
The 140m (459ft) bridge will also link cycle routes throughout the Vale of Glamorgan and Cardiff and would open for river traffic.
The Harbour Authority has carried out a feasibility study and Cardiff councillors say the bridge is a high priority.
The proposals for the Treforest scheme include the provision of a footbridge across the railway line at the University of Glamorgan's Treforest campus to provide a link to residential areas and the university's Glyntaf campus.
Eudine Hanagan, Rhondda Cynon Taf cabinet member for transport, said: "It's extremely exciting for such an innovative project within Rhondda Cynon Taf to have this opportunity to be part of the UK-wide Connect2 bid and we must do all we can to support it.
"The scheme would be a huge boost to what is already a beautiful environment and for Pontypridd generally."
The lines for telephone voting on who should win the Big Lottery Fund are open until midday on Monday.
Online voting started on 26 November and will also stay open until Monday.