The authorities in the northern Nigerian state of Kano have imposed a ban on Muslim men and women travelling together on public transport.
Kano has a history of inter-religious riots
They say the ban is in accordance with Sharia law.
Men and women-only buses and motorcycle taxis were paraded in a mass rally at a stadium in the city of Kano.
Kano is one of several Muslim majority states that adopted Sharia law in 2000, a move which led to inter-religious riots that left thousands dead.
Under the ban, commercial motorcylists seen carrying women could be fined.
Correspondents say the scheme has been quite well-received by all communities as Christians will still be able to use existing non-segregated vehicles.
'Obey your leaders'
The governor of Kano state said a new force of 9,000 uniformed police would enforce the law.
"Our aim is to be at the forefront of conducting our activities decently and to protect Allah's Sharia," Ibrahim Shekerau told the rally.
Muslim cleric Ibrahim Kaliel had a warning for taxi drivers.
"You have no excuse to carry a woman who is neither your wife nor your mother on a motorcycle," he said. "The Holy Prophet Mohammed says you should obey your leaders in all circumstances."
But some drivers said they got most of their revenue from women.
"The government intends to put us out of business by this new law because we can't feed our family by relying on male customers who do not pay as much as women," moped operator Sahabi Malam told AFP news agency.
For and against
Kano is one of 12 northern states which have implemented Sharia law since 2000.
The move initially heightened tensions between Muslims and Christians and led to clashes which left thousands dead.
Human rights groups have condemned abuses sanctioned under the law including amputations and flogging, and say it discriminates against women.
Sharia law appears to have retained popular support in the north.
But there is significant opposition to the law, especially among the Christian minority.
While officially it does not apply to them, many say that in practice they are forced to comply.