(Updates with additional comments from Uber's Urtasun)

By Alessandra Galloni and Joshua Franklin

NEW YORK, April 8 (Reuters) - Uber Technologies Inc (IPO-UBER.N) expects it will be a long time before one of its biggest investments, self-driving cars, is ready for wide-scale deployment, a senior scientist said on Monday, as the ride-sharing firm gears up to go public.

Raquel Urtasun, who is chief scientist at Uber Advanced Technologies Group (ATG) and heads the group's unit in Toronto, spoke about the challenges for self-driving development at a Reuters Newsmaker https://www.reuters.com/newsmakers event in New York.

"Self-driving cars are going to be in our lives. The question of when is not clear yet," Urtasun said. "To have it at scale is going to take a long time."

The more cautious tone marks a change from three years ago, when Uber embraced aggressive tactics to turbocharge its autonomous vehicle development in a bid to get more robot taxis on the street driving more miles. The company had been seen as an industry leader in the technology until one of its autonomous SUVs killed a pedestrian in Tempe, Arizona, in March last year.

Urtasun's comments fall in line with the rest of the self-driving industry, which after much hype and bold promises has tempered expectations and pushed out timelines for deployment. The extreme technical challenges of building cars that can predict human behavior and respond appropriately proved greater than even some of the industry's brightest minds had anticipated.

The progress of Uber's self-driving car unit is in the spotlight as the company prepares to kick off its initial public offering this year. Uber, whose losses before taxes, depreciation and other expenses were $1.8 billion last year, has at times spent close to $200 million in a single quarter on its self-driving unit, sources told Reuters.

Uber, last valued at $76 billion in the private market, is seeking a valuation as high as $120 billion in its IPO and may kick off its investor roadshow before the end of April, Reuters has reported.

"It is true that when you go to an IPO, there is much more of a look into your finances," said Urtasun. "That being said, again because Uber understands that self-driving cars at scale is not something that's going to happen tomorrow, they understand the need for the science."

Urtasun declined to offer any guidance on what mix of human-driven cars and autonomous cars Uber will have in the next 10 years, citing too many uncertainties in the industry.

"What is clear is that in a 10-year timeframe there will be a mix of both (self-driving and human-controlled cars)," she said.