The Napthine government's most senior transport planners detailed the superior economic return a rail tunnel under the city would bring to Melbourne compared with the East West Link, emails obtained by The Age reveal.

The emails show the planners calculated the rail tunnel would return $1.90 for every $1 invested compared with $1.40 for the road tunnel.

But the government dumped that rail plan early this year and has pressed ahead with the $6.8-billion road tunnel. If the Coalition wins next Saturday's election, construction is due to start this year.

The emails detailing the higher "benefit-cost ratio" of the Melbourne Metro project compared with the East West Link were released under freedom of information to Labor.