Asked by members in the Rajya Sabha why police did not spot the bus even after it passed three patrolling vans, Home Minister Sushilkumar Shinde blamed it on tinted glasses.
"Usually PCR (police control room) vans take rounds after an hour. The bus had tinted glasses and curtains," the minister said.
Shinde said that with immediate effect, Delhi Police will crack down on all commercial buses having tinted windows and curtains.
Police would also verify the antecedents of all drivers, staff of all public vehicles and autorickshaws in Delhi. Vehicles run by "unverified staff" would be impounded, Shinde said.
He said the number of PCR vans would be raised.
"We will augment the PCR fleet by adding more vehicles, which will have GPS (global positioning system) so that they can be tracked from the control room," the minister said.
The 23-year-old woman gang-raped by half-a-dozen men in a moving bus here Sunday night is now battling for life at a hospital.
The men tortured and raped her and then dumped her on the road. Her male friend was also thrashed and thrown out of the bus along with her.
Shinde said Delhi Police had ordered that all buses which ply at night would keep their inside lights on.
"All off-duty buses must be parked with the owner, not with the driver or staff. Driver's licences with photos and helpline numbers will be displayed on buses," he said.
Shinde apprised the house about the progress of the police probe, saying four of the six accused had been arrested.
"Police teams are conducting raids to arrest the remaining two. A special investigation team has been constituted," he said.
"A lady IPS (Indian Police Service) officer has been directed to visit the hospital and take stock of the victim's condition daily and help the family members," he added.
Earlier, Shinde met top officials of Delhi Police.