It’s a rule of thumb many motorists have long lived by: Drive less than 10 miles per hour above the speed limit and you probably won’t get a ticket.
As it turns out, that widespread belief generally holds true in Massachusetts.
The odds of being issued a fine for speeding spike dramatically when drivers go 10 miles per hour or more over the limit, according to a Globe review of Registry of Motor Vehicle records of more than 1 million speeding violations issued across the state in recent years.
Of the 1.3 million speeding violation notices police issued statewide from 2010 through the spring of 2016, 98.9 percent were for driving at least 10 miles per hour over the speed limit. The remainder were for driving 9 miles per hour or less above the limit.
“Anyone can drive a few miles per hour over (or under) the speed limit, based on traffic flow,” Mark Leahy, executive director of the Massachusetts Chiefs of Police Association and former North-borough police chief, said in an e-mail. “Most cops give the benefit of the doubt.”
Not everyone gets a break, though. There were nearly 900 violations for driving 4 miles per hour or less above the limit and about 300 for driving just 1 mile per hour above it.
“There is no guiding policy, formal or otherwise, that mandates whether or when to ‘give a break,’ ” State Police spokesman David Procopio said. “We expect troopers to be active and alert, and empower them to use their discretion.”
Officials said other factors probably were at play when drivers were fined for going just a hair above the limit.
There may have been bad weather conditions or they may have been driving through a particularly busy area, near a school or playground, or they may have committed multiple violations.
Brian Kyes, president of the Massachusetts Major City Chiefs of Police Association and police chief in Chelsea, said such a scenario might be: “Traveling at a speed of greater than 30 m.p.h. on a street in Chelsea when school has been dismissed at 2:30 pm when it is raining, snowing or icy is incredibly dangerous.”
John Carr, an activist with the Massachusetts chapter of the National Motorists Association, said he thinks that at least some of the drivers cited for going only slightly above the speed limit may have been rude in some way, prompting the officer to issue a fine instead of a warning.
“Having a bad attitude is definitely part of the story,” Carr said. “You can talk yourself into a ticket.”
But, Procopio said, “Our expectation is that troopers will not base citation decisions on a motorist’s attitude.”
The data also show clear spikes in violations at numbers that end in either a zero or a five, suggesting that police frequently round off the speed they write on tickets.
In some cases, the precise speed matters. In Massachusetts, the fine amount doesn’t change for violations issued to drivers for going 10 miles per hour or less over the limit. But for each mile per hour above that threshold — say, going 76 in a 65 miles-per-hour zone — the fine amount increases by $10.
But police said that whenever they round a driver’s speed, they round down.
If police use radar- or laser-equipped tools that can measure a vehicle’s velocity, “the speeds are exact,” Kyes said. “If not, and officers clock the speed [or estimate it, often based on the speed of the officer’s own vehicle], then the numbers are usually rounded down not up and the motorist gets the benefit of the doubt. This is pretty much the general rule.”
Carr agreed, as did Cambridge attorney Ryan Caselden, whose firm represents drivers who fight traffic violations.
“Oftentimes troopers and officers will give a break on the speed for drivers,” Caselden said. “If they were going to do any rounding, they’d go down.”
The data do not list the roads where the violations were issued. But many were issued in cities and towns with major highways, such as the Massachusetts Turnpike.
Drivers interviewed Thursday outside the Haymarket RMV branch in Boston said that speeding is just a normal part of driving, and that the 10-mile-per-hour threshold makes sense.
“I think that leeway is fair,” said Adam Bryant, 32, of Malden. “I feel [speed limits] are about 10 miles per hour too slow anyway, but people would go over whatever the speed limit is, so I understand.”
Elyana Alajmi, 21, of Cambridge, said she was unfamiliar with 10 miles per hour over the limit being a rule of thumb.
“But I’ve definitely done it,” Alajmi said. “I think it’s a good thing because it takes the anxiety and stress off of going a little over the speed limit when you want to get somewhere faster, especially around Boston.”
Alas, many local drivers are familiar with times when being pulled over for speeding is the least of their issues.
“There’s always traffic, so it doesn’t matter,” said Michael Rameaczek, 21, of Dorchester.