Of the 400 million trucks weighed by portable and fixed platforms or weigh-in-motion (WIM) sensors in the U.S. in 2021, 300,000 received an overweight violation. These tickets resulted from a cumbersome, inefficient process: space to put a scale, a police officer to pull vehicles over and a scale operator to weigh them, even in the cases where WIM sensors were used to initially identify violations. 

“For any urban environment … to be able to pull a truck over [and] put [it] on a portable scale, it's very labor intensive and needs a lot of space,” says Tanvi Pandya, executive director of the New York City Dept. of Transportation bridge division. 

Pandya is an advocate for direct enforcement of weight limits, a legal enforcement mechanism that relies only on WIM sensors: no side of the road scales for initial or secondary weighing, no police officer to issue a ticket. Direct enforcement through WIM is recommended by the World Road Association (PIARC) among other organizations and agencies. 

In 2023, armed with weight data from a federal research grant and permission from the state, New York City became the first and only municipality in the country authorized to use direct enforcement for weight limits, applying the technology and process to the city-owned stretch of the BQE, an 11.7 mile partially elevated roadway that connects Brooklyn and Queens.

“We have to be able to enforce,” says Pandya, “and we need to design [infrastructure] to a known load rather than just guessing based on codes.”

NYC Leads the Way

Overweight trucks are accelerating the structural deterioration of the BQE, portions of which are over 85 years old, according to the NYCDOT. This is happening for two reasons: today’s legal load of 80,000 lb per vehicle is higher than the 1940s design load of 72,000 lb per vehicle.

In 2019, under a federal research grant, the NYCDOT began working with Professor Hani Nassif and his team from Rutgers University, and C2SMARTER, to analyze data from WIM sensors installed on the BQE and understand the magnitude of the issue.   

“We had a lot of anecdotal evidence [but] in reality, because it is so difficult to enforce weight limits in New York City or any other urban environment … we knew there's more weight on the structure” than had previously been quantified, says Pandya.

The results did not surprise Pandya. Ten percent of truck traffic weighed was over the legal limit, some by more than 115,000 lb. They found that site specific loading was 22% higher than what they would get if trucks followed the limits for the BQE’s Staten Island bound direction, and 30% higher in the Queens bound direction.

Weight data was collected using quartz sensors made by manufacturer Kistler, according to JT Kirkpatrick, a Kistler sales manager for traffic solutions in North America. He says the quartz sensor is “the ideal product to use to weigh a vehicle that is doing 100 miles an hour…[it] gives you an accurate instant voltage reading.”

When the data revealed just how many vehicles were above weight limits, the NYCDOT raised the alarm with the city. 

“The mayor at the time issued an executive directive, reminding everybody of the legal weight,” says Pandya. “We also let people know that even if you have an [overweight] permit, you're not allowed on this section because you're way overweight for this structural capacity.”

But the warning wasn’t enough. The NYCDOT needed a way to use the WIM technology to enforce the law, and there was no pathway to do so.

“Because there's no national standard set for high-speed WIM systems, New York City was unable to use them through the existing law enforcement legislation,” says Kirkpatrick, who has been involved in the campaign to get WIM sensors standardized.  

In 2021, the New York State legislature authorized the NYCDOT to conduct automated overweight vehicle enforcement on portions of the BQE, providing a temporary legislative basis for enforcing BQE weight limits. 

In August of 2023, the NYCDOT started a 90-day warning period for trucks on the Queens-bound BQE. Using sensors in the roadbed to detect weight and documentation of the vehicle through cameras, the NYCDOT issued warnings to drivers. The number of Queens-bound overweight trucks on the BQE's triple cantilever dropped 55% between the first and final week of the warning period: 344 warnings to 153. 

Pandya says that from that data alone, it’s hard to know if drivers are simply rerouting, as opposed to reducing their weight. “But, they're certainly avoiding this section of BQE, which is what we need.”

After the 90-day warning period, ticketed enforcement on the Queens-bound direction began and overweight trucks were subject to a $650 fine per weight limit violation. Over the course of the enforcement period, from November 2023 to May 2024, there was a 64% reduction in overweight vehicles along the triple cantilever of the Brooklyn Queens Expressway according to a statement by the NYCDOT. The share of overweight trucks fell from about 6.3% of all trucks on the roadway to 1.9% in the most recent months.

“We’re hopeful that the more we can do enforcement that is 24/7 and make it [in] more places, the more it will be beneficial to be compliant [drivers],” says Pandya. “And so then we don't have this uneven playing field where the truckers that are actually being compliant are losing out in the current system [in which] whoever is willing to take the chance, probably gets a benefit.”

There is also a public safety benefit to discouraging overweight trucks, says Pandya, because heavier trucks take longer to stop. And reducing overweight vehicles can reduce the impacts of tire wear on respiratory health in communities near highways.  

NYC DOT plans to launch direct enforcement for Staten Island-bound traffic by the end of the year.

Scaling It Up

The BQE is not the only roadway where WIM sensors are used: 84% of the 2022 reported violations at the national level were measured by WIM scales. But in other municipalities, standard protocol is that an overloaded truck is detected by a sensor and a photo of the truck is uploaded to a website and retrieved by an officer somewhere down the road, says Kirkpatrick. Then the officer pulls over the truck and reweighs it, as required by law, because standards for WIM scales are not yet established. 

In order to be authorized to conduct direct enforcement, New York City had to propose standards from scratch—define the scale calibration technique, the frequency by which it should be calibrated and tested, and more—and have the standards incorporated into state law. This is a heavy lift for most municipalities. 

Starting in 2021, Pandya, Kirkpatrick, and others began advocating at the national level to amend the National Institute of Standards and Technology (NIST) Handbook 44 to include standardization and specifications for WIM sensors.

“By establishing a national standard in the Council of Weights and Measures, which is run by the Department of Agriculture … any other state that wants to legislate direct enforcement simply has to refer to the national standard,” says Kirkpatrick. 

On July 17, at the National Conference on Weights and Measures, representatives voted on a proposal that would allow the use of weigh-in-motion vehicle scales for direct law enforcement, but the proposal did not pass.

According to NIST Weights & Measures Coordinator Loren Minnich, those opposed contended that proposed test procedures for sensors were extensive and cited lack of funding, personnel and time needed to conduct the test procedures.

But the NYCDOT intends to continue the conversation at the national level.

"We will continue to advocate for the national standards related to this technology to be updated for the benefit of other cities and states maintaining infrastructure,” said NYCDOT Commissioner Ydanis Rodriguez in a statement to ENR.