Is Start/Stop technology really that bad?

“Everybody hates start/stop technology.”

EPA Administrator Lee Zeldin asserted that on social media last spring, going on to say the technology causes “your car [to die] at every red light, so companies get a climate participation trophy.” He vowed at the time that the EPA “is fixing it.” 

Drivers of passenger cars and commercial vehicles alike have expressed annoyance at the intermittent engine shutoffs—typically at red lights and heavy traffic—meant to save fuel and cut emissions. Social media is full of complaints, with one auto technician on X calling start/stop “the most useless modern car feature,” because “it has 10 more additional parts on your car that tend to go out [and] they are all crazy expensive.”

But the question is if fleets should stop or continue using the feature? To answer that, it is necessary to examine how these systems work, potential wear and tear and safety issues, and what benefits they can deliver.

How Start/Stop Works 

While its driver-facing features are straightforward, start/stop technology is not a single system, but rather a family of approaches. Its implementation varies significantly depending on vehicle class and powertrain.

A Cummins white paper, Fuel economy and CO2 improvement potential of Conventional ICE powertrains, outlines a progression of idle-reduction technologies that form the foundation for modern start/stop systems.

Neutral idle, a feature available on the market today works by automatically shifting an automatic transmission into neutral when the vehicle stops, explained Derek Kiesler, director, product strategy at Cummins and co-author of the paper.

“When a truck is stationary but still in drive, the torque converter creates additional load on the engine, forcing it to burn more fuel,” Kiesler explained. “By shifting to neutral, that load is removed while the engine continues to run and power accessories such as alternators, HVAC, and air compressors.”

The results are measurable, added Daniel West, director of emissions strategy at Cummins. For example, neutral idle functionality can provide a 4.6% CO₂ reduction for a Class 6 pickup-and-delivery box truck and 6.3% for a Class 8 refuse collection vehicle.

Automatic engine shutdown (AES), the Cummins paper also related, goes a step further by turning the engine off when it is parked for more than 60 seconds, provided that the engine is not required for PTO operation or climate control and that battery charge is sufficient for restart. When combined with neutral idle, noted Naqash Palathamveed, Cummins product strategy leader, AES can produce 9.6% fuel savings for a Class 6 truck and 11% for a Class 8 refuse truck.

Stop/start technology merges the concepts of neutral idle and AES by shutting the engine down even when the vehicle is stationary but still in drive, such as at traffic lights, explained Ben Stuart, platform strategy leader at Cummins. When stop/start and AES are combined, he reported, total savings can reach 14.2% in fuel and CO₂ for Class 6 vehicles and 15.7% for Class 8 refuse vehicles.

Light-Duty Systems

Evan Xiao, Stellantis head of propulsion systems calibration, explained how start/stop technology works in light-duty trucks and pickups. On the Ram 1500, he related, the eTorque mild-hybrid system uses a 48-volt battery and Belt Starter Generator (BSG), which creates a smoother and more responsive start/stop experience than you’d have with a conventional starter motor.

“When the vehicle comes to a stop, the engine shuts off while electrical systems remain powered,” Xiao said. “As the driver releases the brake, the BSG restarts the engine quickly and smoothly, delivering a transition that feels more like electric assist than a mechanical crank. The system also provides a brief torque boost during initial acceleration.”

Stellantis also offers a 12-volt Engine Stop/Start (ESS) system on select vehicles such as the Ram 1500 with a Hurricane twin-turbo I-6 engine. The system automatically shuts the engine off at a full stop and restarts it when the driver releases the brake using a specially designed heavy-duty starter and deep-cycle batteries designed to handle higher restart cycles.

Mark Haener, sales & service operations director at GM Envolve, reported that General Motors auto start/stop systems across the manufacturer’s vehicle lineup are designed to automatically shut off the engine when the vehicle is stopped. “The vehicles restart instantly when the brake is released or the accelerator is pressed,” he said.

Heavy-Duty Innovations

For medium- and heavy-duty vehicles, manufacturers are refining start/stop concepts to match vocational duty cycles.

Allison Transmission’s Neutral at Stop technology, now standard on Kenworth and Peterbilt models equipped with Allison 4700 Rugged Duty Series transmissions, automatically shifts the transmission into neutral when the vehicle stops in traffic or at lights. When the driver accelerates, the transmission re-engages seamlessly.

According to Allison, the technology minimizes the load on the engine, resulting in reduced fuel consumption. As part of Allison’s FuelSense 2.0 package, Neutral at Stop can contribute to fuel savings of up to 6%, the company added.

Volvo Trucks has taken a different approach with a new generation of their I-Roll technology on the European FH cabover that includes an engine stop/start function at highway speeds. Using road topography and curvature data, the system temporarily turns off the engine when a downhill slope is detected.

“While the engine is off, zero fuel is consumed and there are no tailpipe CO₂ emissions, explained Stefan Elfström, global PR and media relations director. “This innovation can reduce fuel consumption by up to 1% on top of other savings from things like aerodynamics.”

Start/Stop benefits 

Even marginal gains in fuel reduction can scale into significant cost and emissions reductions, manufacturers noted.

Volvo’s Elfström estimates that I-Roll engine stop/start feature cuts emissions by about 1%.

Stellantis, Xiao noted, reports that fleets operating in city-intensive or stop-and-go conditions may see up to a 2-mpg improvement with the Ram 1500 eTorque system compared with non-hybrid configurations.

Cummins’ data for vocational trucks is even more striking. Depending on how technologies are combined, idle reduction and stop/start systems can produce fuel and CO₂ savings ranging from 4.6% to 15.7%, West noted. Applications with more frequent stops, such as refuse collection and urban delivery, achieve the most benefits.

“As idle time is a major contributor to fleet fuel expense, start/stop systems can help mitigate this cost without additional driver coaching,” GM’s Haener said. “Exact savings are dependent on the vehicle use case but generally customers that operate in dense urban environments such as repair services or utility companies would realize greater benefits than those that primarily use vehicles for highway or long-haul driving.”

Wear and Tear

A frequent criticism of start/stop technology is that repeated engine restarts could increase wear on starters, batteries, and engine components. Manufacturers argue the opposite, asserting that the systems should not shorten component life in normal operation.

Xiao said the Ram 1500’s eTorque system reduces mechanical load on the starter by using the Belt Starter Generator instead of a traditional 12-volt starter. “The reduction in idle time also decreases low-load engine wear over the life of the vehicle,” he added. “For vehicles equipped with heavy-duty starters designed for higher restart cycle counts, deep-cycle batteries, and supporting sensors, software calibration ensures long-term durability.”

Cummins frames start/stop as part of a broader strategy of using mature, familiar systems to cut fuel use without compromising uptime or drivability.

At Volvo, Elfström said that its start/stop feature “does not have a significant impact on the wear and lifetime of other components,” suggesting that maintenance benefits are minimal but that no major penalties exist either.

Annoyance or Non-Issue?

While drivers may dislike start/stop systems based on perceived inconvenience or simply the sensation that the vehicle has stalled, manufacturers counter that commercial-grade systems are calibrated to avoid those problems.

“Volvo I-Roll,” Elfström said, “is only activated when it does not compromise driver comfort, particularly in relation to climate control. It is mainly a feature to save fuel and does not impact the driver.”

At Stellantis, Xiao reported that drivers often appreciate the smoothness and added low-speed torque of the eTorque system. “Many describe its transitions as seamless and say it enhances everyday drivability,” he added.

GM is not aware of specific driver concerns tied to its automatic stop/start systems, Haener offered.

Safety Issues

Across the responses from manufacturers, safety concerns are also notably absent.

Volvo’s Elfström said there are no safety issues that would cause a fleet to disengage the feature.

GM, Haener reported, has not seen any safety problems associated with its automatic stop/start systems.

Cummins explained that algorithms are designed to ensure engines only shut down when restart reliability and accessory needs can be met.

The emphasis in all cases is on intelligent controls that check battery charge, diagnostic status, PTO use, and climate requirements before allowing shutdown.

The fleet question: Start or stop

For most fleets, the value of start/stop systems comes down to economics and operational fit.

Volvo’s Elfström argued that any driver concerns—mainly related to air conditioning—have been addressed by activating the feature only when outside temperatures allow. “From our perspective, the business case is clear,” he said. “Fuel savings combined with lower emissions support both profitability and sustainability goals.”

Stellantis takes a pragmatic view. “Each business must evaluate the advantages of technology for their specific use,” Xiao said.

In the Cummins white paper, the company noted that regulatory and market pressures are pushing fleets toward immediate efficiency gains while longer-term zero-emission solutions mature. Idle reduction and stop/start systems are practical tools that can be deployed now, the manufacturer added.

The evidence from manufacturers and suppliers suggests that start/stop systems—whether in the form of neutral idle, engine shutdown, mild hybrids, or predictive downhill engine-off strategies—deliver real, if sometimes modest, fuel savings. 

In short, for fleets operating in dense urban or stop-and-go environments, the business benefits often outweigh driver concerns. For long-haul or highway-dominant operations, the payoff may be smaller but there is still value.

In vocational and urban duty cycles, those savings can exceed 10%. In long-haul trucking, they may be closer to 1%.

For critics, start/stop systems represent an intrusive feature forced on drivers in the name of emissions compliance. For engineers and manufacturers, they are just one element in a layered strategy of efficiency improvements that includes aerodynamics, powertrain optimization, and idle reduction.

In the end, the question may not be whether to stop with start/stop technology, but how to make it smarter, smoother, and better aligned with the needs of drivers and fleets alike.