Rob Blackie, who was last month selected by the party to fight next year’s City Hall election, said the pollution charging system is currently too “blunt” and that people needed more time to fully adapt to the zone’s London-wide expansion.
“What we will be bringing forward will be things to make it better targeted right now,” said Mr Blackie, in an interview with the Standard.
“Right now, if you’re a nurse who drives to a night shift, from somewhere just outside London, or within the outer zone, and then you come back from that night shift, you end up paying twice.
“That’s clearly quite blunt, and you’re probably driving at the least harmful time of day.
“So it’s not terribly well targeted right now. What we will be talking about is making it fairer.”
The 50-year-old digital marketer, who lives in Herne Hill, said this could potentially be achieved by providing more exemptions from the charge in certain circumstances.
But he stressed too that he wanted to see fewer polluting vehicles on the capital’s streets, partly by making improvements to transport in outer London.
“We [the Lib Dems] called for a delay [to the Ulez expansion] because we want it to be successful. In inner London, it has been successful,” he said.
“It’s been a success because people had three years to adapt, and they had better public transport.”
The Ulez, which charges non-compliant vehicle drivers £12.50 per day, previously only covered the area within the North and South Circular Roads, but was expanded last month to take in the whole of Greater London.
Mr Blackie added: “The perfect Ulez is one where you have 100 per cent compliance. The perfect Ulez raises no money at all.
“So obviously what we want to do is make it fair, to encourage environmentally good behaviours and to help people to adapt.”
The candidate is focusing his campaign however around crime, arguing that it has been “Sadiq Khan’s huge failing”. He said that under the current mayor, the Met Police has spent too much time stop-and-searching people for cannabis, and not enough time dealing with rape cases and sexual offences.
He added that the Government’s decision this week to outlaw nitrous oxide - also known as laughing gas - was an “utterly misplaced priority” which will occupy tens of thousands of hours of valuable police time.
The candidate also pledged to support undocumented Londoners who have lived in the capital for a certain amount of time and are facing threats of removal.
This would take the form of a ‘London passport’ - which he said would entitle holders to legal assistance from City Hall, when making their case to the Home Office for citizenship.
Like Conservative candidate Susan Hall, Mr Blackie said he would keep Mr Khan’s programme of free school meals in place for longer than one year, calling it “a fantastic policy”.
He added that it was “the second half of a job started by the Lib Dems”, after the party introduced free school meals for Key Stage 1 children during the coalition government.
On housing, he said he would “examine every way” in which more homes can be built, while “engaging with communities” as part of that.
“It’s increasingly possible to build over things like railway lines - the technology around sound insulation has become better in recent years,” he said.
The Lib Dems face an uphill battle in winning the mayoralty. The party has come fourth - behind the Greens - in the last three mayoral elections, and has failed to gain more than 5 per cent of the vote in each, causing them to lose their £10,000 deposit.
But Mr Blackie insisted it was still possible to win, arguing that the party has “a very large liberal voter base” and that “the Conservatives have given us a huge opportunity” by selecting Ms Hall, who having previously expressed support for Brexit and Donald Trump, is “really out of tune with modern London”.
The election will be held on May 2, 2024, with Labour’s Mr Khan standing for an historic third term. Alongside the Tories’ Ms Hall, the Greens have chosen Hackney councillor Zoë Garbett, and Reform UK - formerly the Brexit Party - has selected Howard Cox, founder of the Fair Fuel UK campaign.