Kenya's commuters have been struggling to get to work, after a safety crackdown forced tens of thousands of minibus taxis off the roads.
No overcrowding will be tolerated
The minibuses, which are by far the most popular way for Kenyans to travel, were ordered to install seat belts and a speed limiting device.
The measure is intended to cut the country's high accident rate, but less than one in 5 registered "matatus" met the end of January compliance deadline.
This leaves some 30,000 registered matatus, effectively off the roads.
Long queues of people waiting for the buses have been reported across the country. Many have had to walk to work.
Some commuters have supported the new government regulations despite the biting transport crisis in most parts of the country.
Multi-coloured matatus are not now allowed
"We would rather suffer for a while and have a safe and comfortable mode of transport. We have suffered at the hands of these operators for too long," said Charles Kibe, who trekked 18 kilometres to the city centre on Monday morning.
Since Sunday, when the new regulations came into force, traffic policemen have been impounding hundreds of vehicles nationwide that are not complying with the regulations.
The BBC's Wanyama Chebusiri in Nairobi says many garages are working round the clock as the matatu operators get safety equipment installed.
Some operators who have complied with the rules have doubled their fares.
A spokesman for the Transport Ministry denied that there was chaos on the roads and blamed the matatu operators.
"It's the way these people left everything to the last minute in the hope that the minister would backtrack," Odongo Manyala told the Daily Nation newspaper.
But the chairman of the Matatu operators Association, Simon Kimutai, says it costs about $800 to install the speed governors and seat belts and many operators cannot afford it.
A BBC reporter in Nairobi says the transport crisis is expected to fizzle out later in the week as more and more matatus comply with the regulations.
The new regulations also require the matatus to sport one colour and have a yellow strip.
This will in effect bring an end to the spectacular colour parade that has long been associated with the public service vehicles.
In addition matatu drivers and conductors will have to wear uniforms and badges.
According to police statistics, 3,000 people are killed on Kenya's roads every year, with half of these deaths being blamed on matatus.