Merseyside police released an update on Wednesday in which they revised the number of casualties from 65 to 79, after identifying "more people who were injured."
Seven people remain in hospital after they were struck by the Ford Galaxy on Water Street after 6 pm on Monday.
The force said the suspect, a white man from West Derby, can be questioned until Thursday after he was arrested on suspicion of attempted murder, dangerous driving and driving while unfit through drugs.
The street where the collision took place has since reopened to traffic and pedestrians after a police cordon was lifted.
Under laws around detention, police forces can keep a person in custody for 24 hours without charge, while a superintendent can extend this by 12 hours.
After this time, an application can be made to a magistrates' court for a further 12-hour extension up to 96 hours.
A suspect can be held for up to 14 days without charge for a terrorism-related offence, but police said this incident was not being treated as terrorism.
'Significant progress'
Merseyside police said on Wednesday that significant progress was being made "to establish the full circumstances that led to what happened" and appealed for people not to speculate.
They also asked people to refrain from sharing distressing content online.
Detective Superintendent Rachel Wilson said: "I'm pleased to say that the number of people in hospital is reducing as they continue to recover from the awful incident.
"We continue to support those still receiving treatment, and as part of our ongoing enquirie,s we are identifying more people who were injured.
"We have already had an incredible response from many of those who were there on the day, and I thank them for their cooperation with our investigation.
"I would encourage anyone who has not yet contacted police who may have information on this incident to do so," she added.