You might want to consider a generous tip the next time you get out of a taxi - your driver is going to be facing a tough few decades.

Revenues collected by ride-hailing services like Uber and Lyft, are likely to grow eight-fold by 2030 to $285 billion, leading to a 50% decline in the about $108 billion global taxi market, according to a note published by Goldman Sachs.

Actually, you may want to tip your Uber driver a little extra too, they aren't likely to fare much better according to the investment bank, which is also predicted that as many as 6.2 million chauffeurs and drivers will be replaced by the arrival of autonomous fleets by 2030.

In fact, about the only group involved in ferrying you around that you shouldn't feel sorry for are the car makers. The total sum of cars sold annually in the 100 wealthiest cities is likely to rise from about 20.7 million in 2016 to 23 million by 2030.

"We expect car sales to hold up well relative to the number of cars on the road owing to the significantly faster (by 3.5X) replacement rate of shared vs private cars," noted Goldman Sachs. "This difference in velocity is due to the higher utilization of shared (23k annual miles) vs. private cars (5.9k)."

Better still for car makers, their own mooted shift into running autonomous fleets could boost their earnings per car by about 7X from an average EBIT of $2,000 per new car sold to about $14,000 per new autonomous fleet car put into service. The lure of those profits helps explain why Ford (F) - Get Report this week replaced its CEO Mark Fields with the head of its autonomous vehicles unit Jim Hackett.

"Based on today's average fare of (we estimate) $8.9, the ride hailer makes $2 per ride (23%) and the owner-driver gets $6.8," according Goldman Sach's calculations. "If the fleet manager would be willing to undercut the owner-driver by 20%, the fleet manager would receive $5.5 per ride. Such a car might reasonably be utilized for 15 rides per day. Over its three year life, this gives a revenue potential per car of $90k."

Those sorts of figures also explain why Morgan Stanley analyst Brian Nowak this week told clients that Alphabet's (GOOGL) - Get Report Waymo, autonomous car unit, could be worth $70 billion as a potential spin-out candidate.

But before you get too generous with your tips you might want to consider one last point: the cost of hailing an autonomous car is unlikely to be significantly cheaper than today's chauffeured trips.

"Savings (from paying drivers) may not be passed onto customers: instead, these would likely be absorbed by the cost of operating fleets," Goldman Sachs noted. "The technical content of the car (especially while the technology is young) will make it substantially more expensive than a conventional vehicle. Technology companies, suppliers, and OEMs (original equipment manufacturers) all hope to recoup many millions of development miles financially. "