How Aggressive Driving Impacts an Electric Fleet

 In Fleet Management

We’re all familiar with the phrase “time is money,” particularly as it relates to business. When it comes to operating vehicle fleets though, you’re almost always better off driving with a lighter touch. This is particularly true for plug-in cars.

Thanks to their heavy battery packs, plug-in electrics suffer efficiency and range costs from high speeds and hard accelerations even more severely than conventional cars (ICEs).

All-electric vehicles have large battery packs and are much heavier than ICEs, which exacerbates these impacts. Plug-in hybrids have lighter battery packs and may not lose quite as much electric efficiency, but on trips that outstrip their ranges, every electric mile lost translates to added gas use—and gas is typically several times more costly than electricity on a per-mile basis.

Vehicle mass and eco-score sensitivity

The correlation between vehicle mass, aggressive driving, and fuel consumption.

In the moment, whether we’re running late or simply enjoying the freedom of the open road, many aggressive driving practices seem to come naturally. With the exception of emergency responders though, speeding to our destination as quickly as possible rarely shaves enough time off of a trip to make it worthwhile.

According to a 2008 study by the Monash University Accident Research Center, aggressive driving practices on urban roadways save an average of just one minute for every half hour behind the wheel—about 3.5 percent of total driving time.

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Once you consider the added danger, fuel cost, vehicle wear, and minimal time savings resulting from flooring that accelerator, chances are you’ll prefer that your drivers take their time.

Aggressive Driving Factors

Targets for safe driving programs can best be focused in three areas:

Speed

Plug-ins like the Chevy Volt, Nissan LEAF and Toyota Prius Prime are built for maximum efficiency and have far lower drag coefficients than most conventional vehicles. Nevertheless, their heavier weights exacerbate energy losses due to air resistance.

In a blog post, Tesla’s lead engineer shared his company’s calculations for the Model S’s energy use at different speeds.

At 60 mph, the Model S uses about 250 watt-hours of battery capacity per mile. At 75 mph, that number jumps to about 325 watt-hours per mile. That’s a 30-percent decrease in efficiency netting just a 25-percent increase in speed. Driving at higher speeds also significantly increases the frequency and severity of brake use after acceleration.

Tesla Motors vehicle speed data for the Model S.

Tesla vehicle speed and energy consumption data for the Model S.

Hard Braking

In 2013, we released a study based on aggressive driving data collected from conventional internal combustion (ICE) vehicles. The data showed fuel economy losses of 30 percent or more resulting from frequent hard braking.

Thanks to powerful, energy-capturing regenerative braking systems, electric vehicles aren’t quite as bad in this area.

If we extrapolate the loss in efficiency to the average EV (subtracting the roughly 10-15 percent overall fuel economy improvement offered by regenerative braking,) plug-ins appear to lose about half as much efficiency from hard braking compared to ICEs.

Hard braking and fuel economy

The effect hard braking has on fuel economy.

Hard Acceleration

Hard acceleration is the most powerful culprit in efficiency and range loss due to aggressive driving.

According to one Carnegie Melon study, frequent flooring can lead to as much as a 45-percent efficiency loss in the most extreme cases. These losses are at their greatest when accelerating from a stop, but even in highway situations, they can still represent major battery drains.

Hard Accelerations and fuel economy

The effect hard acceleration has on fuel economy.

Using Telematics to Curb Aggressive Driving Behaviors

A study by the Institute of Transportation Studies at the University of California, Davis, found that using telematics cuts energy usage for the average driver by about 3 percent. Paired with training and continued monitoring of data, that number can grow to as high as 10 percent.

Telematics systems can provide fleet managers and drivers with a number of data points relevant to aggressive driving, including average speed, percentage of hard braking events, percentage of hard acceleration events, and a composite measure called Eco Driving Score. Eco Driving Scores are based on a scale of 1-100, and provide an easily comparable reference that can be tracked over time.

Electric vehicle telematics

FleetCarma telematics for electric and gas vehicles.

As part of the 2013 aggressive driving study, we provided a number of recommendations for ways fleets can use telematics to educate drivers and reinforce safer, more efficient practices. Among them:

1) Consistent Feedback

In order to improve, drivers need to know how they’re doing. This means providing them with access to data before, during, and after any training program.

2) Goal Setting and Management

Once training is complete, provide goals for reducing the frequency of events like hard braking and acceleration—or for increasing a driver’s overall Eco Driving Score.

3) Driver Incentives

Incentives can be tricky to structure but they can also help to deliver fast results by keeping the importance of driving practices fresh in the minds of employees.

4) Prioritize the Process, Not the Result

It’s important not to overdo it with incentives—particularly those linked to negative ramifications or cash rewards. Don’t give drivers a reason to resent your efforts or to attempt to fudge results.

A Powerful Tool for Saving Money, Lives, and the Environment

Before plug-in electric vehicles were reintroduced to the market in 2010, a report from the State of Washington’s Department of Ecology identified curbing aggressive driving behaviors as one of the cheapest, easiest, and most immediate steps that can be taken to reducing greenhouse gas emissions from automobiles.

The case for slowing down is even stronger from a safety perspective. Though there have been surprisingly few studies done on the subject, the American Automobile Association estimated that aggressive driving was a factor in an astounding 56 percent of fatal crashes between 2003 and 2007.

Over the long term, improving awareness around safe driving practices can save you money on insurance premiums and energy costs—all while keeping your employees and the environment healthier. No matter how you look at it, reducing aggressive driving is well worth the effort.

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