Several Google employees tasked with designing the company’s automated cars have left after being paid so much they became independently wealthy, according to a report from Bloomberg.

In an attempt to retain their best talent, Google reportedly used an “unusual compensation system” based on the perceived worth of the project. This system led to employees receiving enormous multi-million dollar bonuses, as well as equity in the business.

It is not clear how much Google spent, but according to CFO Ruth Porat, the 14 per cent rise last year in operation expenses to $6.6 billion for the division was “primarily driven by R&D expense, particularly affected by expenses resulting from project milestones in Other Bets established several years ago.”

However, the compensation system has had the contrary effect, as labor turnover from the company’s car division increased in 2016. According to Bloomberg’s sources, many felt no financial incentive to stay with the Google, while others became frustrated with the pace of the project.

Over the last year, the project lost key figures such as its head of division, Chris Urmson, as well as former executive Bryan Salesky, whose own self-driving start up Argo AI last week received a $1 billion investment from Ford.

Companies developing self-automated vehicles will face the challenge of overcoming tight regulations that could threaten the viability of autonomous vehicles on U.S. highways. Last May, Google urged the U.S Senate Committee to fast-track self-driving cars by waiving states’ rights with a federal takeover of all roads and highways.

The recently confirmed Secretary of Labor, Elaine Chao, told the Senate that excessive regulation “dampens the basic creativity and innovation of our country,” and promised to avoid a “patchwork” of regulation in the rollout of self-driving cars.

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