The 47-year-old actor reprises his role as CTU (Counter Terrorist Unit) agent Jack Bauer in the next installment of the action series, where he finds himself on the run in England's capital, and he admits he struggled to cope with the amount of road users in the city, insisting Los Angeles is "empty" by comparison.
He told the Daily Star newspaper: "Jack Bauer has been through some pretty dangerous and tricky situations in his time.
"But I don't think he has ever had to deal with anything as bad as London traffic.
"I mean seriously, I forgot how intense it is, it makes the roads in LA look empty."
Kiefer shares a "real connection" with London since he was born in the city before his family moved to California where he lived until him and his mother settled in Toronto where he was schooled.
He added: "I love London and England, though. I was born there and have a real connection with the country. So it is special for the new season to be set there."