You don’t need to be a transportation engineer to know that there is a problem when the cars back up on the Portland waterfront.

Especially during the summer, traffic gets stuck in both directions most of the day and into the evening. It not only frays tempers and wastes time and money, but also fouls the air as vehicles move forward an inch at a time.

But if you were a traffic engineer, what problem would you be trying to solve when you looked at the line of cars?

Is it too many tourists looking for parking? Too many pedestrians crossing Commercial Street? Or is it an issue of drivers who became used to crossing Portland quickly on Commercial Street being slow to change their habits?

Or is it some combination of all of those, and in what proportions?

For decades, transportation planners have relied on models based on sophisticated guesswork to determine how to best move people from one point to another. But now, thanks to GPS technology and ubiquitous smartphone use, they have a new tool that tells them not only where traffic gets stuck, but also where each car, truck, bicycle and pedestrian contributing in the traffic came from. It’s information that could lead to more efficient infrastructure investment and safer, more fluid transportation.

But like so much of what we gain by advances in data analysis, it comes with a cost. Who else has this information, and what might they do with it?

Four state and local transportation agencies led by the Maine Turnpike Authority have recently subscribed to San Francisco-based Streetlight Data for detailed data on traffic flows, gleaned from trillions of records collected by voluntary location-based service apps on GPS-equipped smartphones.

The company says its data include no personal or identifying information, but knowing where a trip began can often tell you a lot about who is taking it. It’s important to know who has access to the date and where and for how long it will be held to know whether this is a threat to people’s privacy. Peter Mills, executive director of the Maine Turnpike Authority, is asking the right questions as the service is implemented. In the wrong hands, the same database that can give you the origins of a traffic jam could also be used as an after-the-fact tracker to document someone’s movements.

Without adequate privacy protections, we won’t be able to make full use of this kind of technology. Just as electronic medical records can save lives in an emergency only if people have full confidence that the information can be used only as intended, explicit steps should be taken to make sure that information is really is anonymous and secure.

We look forward to the Maine Turnpike Authority, the state Department of Transportation, the city of Portland and PACTS, the regional transportation planning agency, can make good use of these data in their planning efforts. We also expect the agencies to continuously assure the public that they are protecting this information from misuse.