A major design fault has been detected in the Padma rail link project midway through its implementation for keeping height gap between approach roads and rail tracks lower than standard.
Sources said this fault would block heavy vehicles crossing the country's longest bridge.
The Padma Multipurpose Bridge project being implemented by the Bangladesh Bridges Authority (BBA) recently identified the fault.
It has directed the Padma rail link project (PRLP) to change the height as per the standard of the roads and highways department.
Sources said height clearance between approach roads on Mawa and Janjira sides of the bridge and the rail track is lower than the standard 5.7-metre vertical and 15.5-metre horizontal clearances.
"A black spot has already developed as the Padma rail link project didn't follow the standard design," said bridges secretary Belayet Hossain.
Talking to the FE, he said the matter was brought into the notice of the railways secretary and the director general (DG) of Bangladesh Railway to fix the problem.
The BBA has been implementing the two-tier 6.15-kilometre bridge keeping the road on the top layer and the rail on the lower.
But the BR is responsible for building rail tracks on either side of the bridge.
The rail track is supposed to cross over the approach roads which the BBA built three years ago.
Mr Hossain said the design of the already built approach roads cannot be changed, but there is a need to change the overall design.
However, sources said the Chinese firm responsible for doing the BR's part on the project did not follow the standard set in 2005.
It has already done the work of a pier cap based on the present faulty design.
Padma bridge project director Shafiqul Islam said they have shared their observations with the BR and requested it to change the design.
However, Padma rail link project director said the design fault in the project is not major and it will be done within 15 days.
"Only one pier design would need to change and we're trying to change it," he told the FE over phone.
BR DG Mohammad Shamsuzzman also denied the allegation of a design fault but said the BBA would have raised the issue when the design was shared.
Against the 15.5-metre horizontal gap, sources said, the rail link project has kept 9.0-metre gap on Janjira side and 10-metre on Mawa side.
The vertical clearance has been 5.2 metres against the standard 5.7 metres.
The FE tried to reach contact person John Zhong of the Chinese builder for comment but his cellphone was switched off.
The Padma bridge project has faced multiple problems, including faulty design, since its inception, leaving it to face more than a year's delay in building the main bridge in 2016.
The rail link project also faced similar problems at the initial stage at the time of confirming the design.