Mr Simpson was stabbed in the head and shoulder in the attack
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Father-of-five Younis Khan is the third taxi driver to be killed in Yorkshire in the past year.
Mahmood Ahmed, 36, was stabbed to death in Keighley in April 2006, while Mohammed Parvaiz was murdered by a gang in Huddersfield in July.
Editor of trade magazine Taxi-Today, Tony Mite, said he believed the profession had become the "most dangerous" in the country.
He said attacks happened at any time during the day and night.
One driver who survived a vicious attack was Bill Simpson who was attacked in Leeds while at work three months ago.
'So scared'
Mr Simpson was stabbed in the back of the head by the hooded man who tried to rob him of his takings.
He said: "I was so scared. I wouldn't wish it on my worst enemy."
Police in Sheffield have said they will increase patrols following the murder of Mr Khan, who was shot in his cab as he drove along Scott Road, Pitsmoor, early on Wednesday.
Mr Mite said more needed to be done to protect taxi drivers.
"Drivers are being abused on the school run right up until kicking out times of the pubs.
"They are asking for cameras and also asking for anything else that can be done to bring down the numbers of incidents."
Installing CCTV cameras into taxis was crucial to reducing attacks on drivers, he said.
"The biggest problem is the funding of the CCTV, but it is going to give them a lot of security.
"If there is an issue within the vehicle it picks up the speech, it picks up the pictures and can be used later in any court case.
"It is a big issue, I believe it is the most dangerous job now going - that includes the police and firemen - where more people are injured and verbally abused and even killed."