"No Turn On Red" signs really get Maryann Merigan's haunches up. But none does more so than the one on Walnut Street, where it intersects with Mt. Auburn Street in Watertown, where I met up with her.

"I can’t help but think it’s almost as if I can’t be trusted to know when to turn on red," she said.

Merigan reached out to us at the Curiosity Desk because she wanted to understand more about who decides when to restrict a right turn on red, and how that decision is made.

"I am curiouser and curiouser about who sets the rules for no turn on red at our intersections," Merigan wrote in an email. "Is it done by town? Is it done by the state? I'm pretty sure most of us know how to stop and then turn on red. I would love to know who is in charge of making those decisions."

Merigan is actually pretty lucky she can turn right on red at any intersection here in Massachusetts. As it turns out, it's a recent phenomenon around here. It came to pass because — of all things — unrest in the Middle East in the early 1970s, and the decision by 11 nations there to stop selling oil to the United States in retaliation for our support of Israel.

The oil embargo pushed gas prices sky high here in the U.S. In response, Congress passed the sweeping Energy Policy And Conservation Act of 1975. As part of that legislation, the federal government required each state to come up with its own energy efficiency plan and offered money to help. But that money would only be allocated to states that had "... a traffic law or regulation which, to the maximum extent practicable consistent with safety, permits the operator of a motor vehicle to turn such vehicle right at a red stop light after stopping."

The thinking was that allowing a right turn on red would cut down on idling at traffic lights and therefore reduce gas consumption. Turning right on red was already legal in some states. Congress wanted it legal in all states.

Massachusetts was — in fact — the last state to allow right turns on red, and it appears the state made the allowance grudgingly. When it became legal in Massachusetts in 1980, some 90 percent of the state’s intersections were outfitted with a "No Turn On Red" sign. Then — as now — it's up to officials in each city and town to decide which intersections in that community should get a "No Turn On Red" sign.

In Watertown, where Merigan lives, Steve Magoon is one of a team of officials who make those decisions. He says there are three reasons why they choose to restrict right turns on red.

The first has to do with the flow of traffic and the timing of other nearby traffic lights.

"For example, if people made a right turn on red but then had to stop shortly after, it could back up into the intersection," he explained.

Reason number two is about sight lines. If officials deem that a driver can’t see far enough down the road to spot oncoming traffic, they won’t allow a turn on red.

Reason number three is the most common reason: Protecting pedestrians who might be crossing the street.

"If you allow someone to turn right on red and that person making right turn on red is looking for vehicles to their left, they are not looking for pedestrians on their right," said Magoon. "You can create serious situations there."

For years, environmentalists pushed for fewer "No Turn On Red" signs, since less idling means fewer carbon emissions. But Matt Casale, transportation campaign director at MASSPIRG, says that to really move the needle on emissions reductions, what we really need is fewer cars on the road.

"The environmentally sound thing to do is to be adopting policies that make it easier to walk and bike, make people feel safer," he said. "I actually don’t have a problem with more 'No Turn On Red' signs."

Back at the intersection in question, I shared what I learned with Merigan. She was glad to know who makes the call. And while she says she does understand that the signs are about safety, she still thinks that town officials are a little too "No Turn On Red"-happy.

"I just haven’t seen too many intersections [where] I shouldn’t be trusted to be able to know when I can turn on red," she said. "I’m pretty good at it."

But does she think that the average driver is as conscientious and "good at it" as she is?

"That I don’t know," she said. "I can’t say that that’s the case."