The way Lauren Isaac sees it, the world is looking at two possible transportation futures.

In the "driverless nightmare" scenario, personal self-driving cars governed by a central Big Brother-like information system will not only cram roadways with owners lounging in the backseat, but also add to congestion with owners using the cars as oversized robotic assistants to run errands unattended.

Alternatively, a "driverless utopia" might entail a world of mostly shared self-driving car fleets, leading to fewer overall cars and better meshing with transportation options like high-speed rail while also offering wider access.

The catch: as appealing as the latter might sound — and with electrification likely to lower carbon emissions in either scenario — both options are actually likely to increase the gross number of vehicle miles traveled, said Isaac, manager of transportation sustainability at Parsons Brinckerhoff Engineering Services, at a Silicon Valley auto tech summit held Wednesday.

Along with the question of how to deal with ongoing automotive dependence are several other make-or-break dilemmas likely to keep carmakers, mobility startups and city planners busy in the years to come:

1. How will mobility technologies merge?

With parallel innovations happening in shared cars, electric cars and self-driving cars, an increasing number of analysts expect the technologies to ultimately converge.

But where does that leave us with adjacent developments, like electric bikesharing (Swiftmile, Mahindra) or on-demand commuter carpools (Ride, Lyft, Daimler)?

"The future will be multi-modal," according to Johnny Simkin, co-founder and CEO of transportation analytics and aggregation company Swiftly.

Stay tuned for what that means for personal car ownership rates, first-mile and last-mile transit connections and many other facets of the mobility world.

2. Is it possible to incentivize sustainability?

As projections like Isaac's show, a world with more shared cars and even self-driving cars doesn't necessarily guarantee a world with less driving.

While vehicle miles traveled have long been a go-to transportation metric in environmental circles, the proliferation of electric vehicles could change the calculus behind existing issues like automotive emissions. Still, more driving would also likely mean more roads and road maintenance, plus the potential for an increasing gap between those able to afford or not afford more fragmented mobility solutions.

Emily Castor, director of transportation policy at Lyft, urged cities to consider charging more for parking to discourage personal car trips and said the company is working with investor General Motors on ways to offer drivers without personal cars the usage of company EVs.

On the issue of access, Castor added that Lyft and others would be wise to explore options for "bank-less" consumers who rely on cash to buy transportation, as opposed to credit card-linked apps. A related question is whether ridesharing might opened up for government subsidies in areas where it is currently expensive to subsidize low-density mass transit.

3. Just how big might Big Brother be?

Some of the headier obstacles in the pursuit of sustainable transportation systems tie back to privacy and security. Specifically, what it means for consumers if and when connected self-driving — potentially all-encompassing surveillance bots — go mainstream.

Whether it's possible to segment data collection between multiple providers, guarantee data privacy or add in layers of security are all issues in play. If more centralized models win out, with automakers or large tech firms like Google and Apple providing both hardware and software for future cars, those issues could get dicier.

Cars collect a lot of data. They know where you’re going.

Still, it looks more likely at the moment that private sector players, rather than public agencies, would even have the capacity to develop and utilize these data-intensive networks.

“I don’t think the government will be in a position to be playing God," Isaac said. "It will be the different operators that will be in the position to parse that."

Stephen Wu, an attorney with Silicon Valle Law Group, added that there is potential to divvy up self-driving car monitoring and analysis geographically, as the aviation industry already does.

“It could be like air traffic control, where you’re handed off city to city or region to region," Wu said.

4. Who’s liable for what?

In the category of major logistical hurdles are several big questions about how a growing array of transportation technology providers — not only automakers, but software providers, data analytics companies and cloud service businesses active on the back end — might be impacted by looming legal battles.

Similar to the drone industry, Wu said determining baseline legality in terms of issues like where it's even legal to drive a self-driving car will be the first hurdle.

Then there's the likelihood of a new generation of liability lawsuits over who is held accountable when things go wrong. That could be either from a safety perspective, like GM's deadly $4 billion ignition malfunction, or issues of fraud, such as Volkswagen's diesel emissions cheating scandal projected to cost the company up to $7 billion.

"These are very expensive liabilities," Wu said. “Who could be responsible?"

5. Public transit agencies: The next big mobility providers?

With the constellation of private players eyeing the auto tech space growing ever bigger, perhaps the biggest question for society at large is what that all means for taxpayer-funded public transit systems by definition meant to service all segments of society.

In many cases, that means turning to technology to help modernize offerings.

"Transportation agencies are seeing themselves now more as mobility providers than infrastructure providers," Isaac said. "There’s so much lower risk because it’s less investment."

In Silicon Valley, a suburban and congested patchwork of dozens of disparate cities in a relatively compact area, the Santa Clara Valley Transportation Authority has for years plagued by low ridership of public buses and light rail services. The agency has also had to adjust quickly to new variables, like the region's famous Google buses.

Now, Chief Information & Technology Officer Gary Miskell said the agency is aiming to better incorporate popular services like Uber and Lyft, which could spur residents to reconsider transit.

“We are talking with them about how to solve first-mile, last-mile," he said.