The Thailand Consumer Council (TCC) on Thursday called for a complete inspection of the Yellow and Pink Lines, the country's first two monorail systems.
Questions have been raised over whether errors occurred during the system installation on the two lines following two recent mishaps, it said.
The TCC was responding to this week's incident on the Yellow Line and one last week on the Pink Line.
On Dec 24, a section of conductor rail on the Pink Line broke free from its beam and fell onto a street damaging several parked cars parked along Tiwanon Road in Nonthaburi. The incident prompted the suspension of services on the line.
Meanwhile, on Tuesday evening, a guide wheel fell off a Yellow Line train and landed on Thepharak Road below before bouncing and hitting a taxi.
Both incidents have raised safety concerns, said the TCC in a statement published on its website on Thursday.
Assoc Prof Chalie Charoenlarpnopparut, a member of a TCC sub-committee on transport and vehicles, said the incidents appear to have been the first of their kind on a monorail system anywhere in the world.
To support his observation, he cited findings from his own research into other monorail systems which revealed no other similar incidents occurring in other countries.
That's why it is now crucial for the two companies contracted to install the Yellow and Pink monorail systems to prove they are safe by conducting an intensive inspection of both systems, he said.
"I don't think the problem is with maintenance on these two lines as they are both newly installed and began operating not long ago," he said.
He also urged both companies to consider adding metal netting in certain spots to prevent a train from falling to the ground in case one is accidentally dislodged from the single concrete girder along which it runs.
This type of protection system exists in other countries which began using monorails before Thailand, he said, adding that from his own experience, monorail trains in other countries do not rock and shake as much as they do in Thailand.
Eastern Bangkok Monorail Co, the concessionaire of the Yellow Line project, and the Northern Bangkok Monorail Co, the concessionaire of the Pink Line project, both said they were still investigating their respective incidents.