This comes after the rail link between Hatfield and Pretoria stations was closed around 8h30 on Thursday morning allegedly due to a derailment of the Gautrain.
Hundreds of passengers were forced to use alternative transport after they were evacuated from the Gautrain following the suspension of operations as a "minor derailment" occurred when the train approached Hatfield station.
Democratic Alliance (DA) Gauteng spokesperson on roads and transport, Neil Campbell, accused the GMA of keeping the investigation away from the public.
"A derailment of a Gautrain cannot be shrouded in the secrecy which the Gautrain Management Agency seems to employ when problems arise on the network," Campbell said.
"If the closure was due to a derailment, an internal investigation will not be sufficient to reassure the public that the train is safe to ride."
Campbell said this would be an ideal opportunity for the Rail Safety Regulator to investigate the matter, but it was unlikely that they would have the capacity to do so given the financial constraints on the regulator.
In response, GMA senior executive manager of communication and marketing, Barbara Jensen, said the Rail Safety Regulator was in any such incident, in any case, involved in the investigation.
"The Gautrain Management Agency is waiting for the findings to come in and then will release information to the public. Nothing is shrouded in mystery," Jensen said.
But the DA seemed unsatisfied.
Campbell said that the MEC for Roads and Transport, Ismail Vadi, must establish independent inquiry into Gautrain derailment.
"The DA is of the opinion that independent experts must be appointed and report back to Gauteng Roads and Transport MEC, Ismail Vadi and the Provincial Portfolio Committee who must be convinced of the train's safety," Campbell said.
"The public has a right to know why the train derailed as a matter of urgency."