Ask any electric car enthusiast about the driving range of their favorite ride, and you'll get two different answers depending on where they live. There's the Environmental Protection Agency (EPA) rating in the United States, and the Worldwide Harmonised Light Vehicle Test Procedure
(WLTP) rating in Europe or other parts of the world. (Except for China, which has yet another, different rating.)
Confusing, right? The problem is that the range ratings are almost certainly different, even if the car itself is the same across these different global markets. Usually, the WLTP figure is higher than the EPA rating. Take the second-generation Nissan Leaf with the 40-kilowatt-hour battery, for instance. According to the EPA, it can go up to 151 miles on a full charge, while the WLTP rating is 170 miles. That's a pretty big difference.
But why? And more importantly, which range rating is closer to reality? It all comes down to how these cars get tested for their range, and the different procedures used to do this.
I’ll start by saying that both testing procedures are done in a controlled environment on a dynamometer, or dyno for short, which is like a rolling road. The room temperature, travel speed, and stopping times are meticulously adjusted and monitored so that all cars benefit from the same conditions. However, there are some differences that eventually lead to the final range figures being different. Let's dive deeper.
How the Environmental Protection Agency (EPA) tests electric vehicles (EVs)
Typically, automakers will come out with range estimates for their EVs (as well as fuel economy estimates for gasoline cars and hybrids) until they can do their official EPA-certified testing. The car companies themselves do this test and then submit their results to the EPA, though the agency also does a small amount of auditing itself.
Since 2008, internal combustion engine vehicles have had to go through five driving routines for EPA testing, which are also called cycles or schedules, that try to replicate real-world city, highway, and high-speed driving conditions, as well as tests where the air conditioning system is engaged and a procedure where the ambient temperature is lower than the normal procedure temperature of 68 to 86 degrees Fahrenheit (20 to 30 degrees Celsius.)
The EPA has also established slightly different testing criteria for EVs and PHEVs. According to these, battery-powered vehicles have to go through three testing procedures. In the case of EVs, these are the Single-Cycle City Test, the Single-Cycle Highway Test, and the Multi-Cycle City/Highway Test. Before this happens, the high-voltage battery is fully charged with the manufacturer’s charger, and the car is parked overnight.
For the Single-Cycle City Test, an EV is put on the dyno and driven over successive city cycles until the battery is completely discharged and the vehicle can no longer follow the schedule. Then, the battery is recharged from an AC source and the energy consumption of the EV (in kilowatt-hours/mile or kilowatt-hours per 100 miles) is determined by dividing the kWh of energy to recharge the battery by the miles traveled by the car.
The recharge includes any losses due to inefficiencies of the carmaker’s charge. To determine the energy consumption in MPGe, which is the miles per gallon equivalent, the EPA uses a conversion factor of 33.705 kWh per gallon of gasoline, while the city driving range results from the number of miles driven on the dyno on the city cycle until the car can no longer move. However, this isn’t the whole story, but more on this a bit further down.
The city test cycle is the same that ICE cars are submitted to but in the case of EVs, the schedule is repeated until the battery can no longer power the wheels. The test is meant to simulate a low-speed trip in stop-and-go urban traffic where the top speed is capped at 56 miles per hour (90.1 kilometers per hour), the average speed is 21.2 mph (34.1 kph), the maximum acceleration rate is 3.3 mph/second (5.3 kph/s), and the distance is 11 miles (17.7 km)—although remember that EVs go through this test multiple times.
A complete cycle lasts for 31.2 minutes and involves 23 stops that result in an idling time of 18%. The car’s air conditioning and heater are turned off.
It’s a story similar to the Single-Cycle Highway Test, only this time the car is subjected to the typical Highway test, where real-world free-flow traffic conditions are simulated. The top speed is capped at 60 mph (96.5 kph), there are no stops, and the simulated distance is 10.3 miles (16.5 km.) But again, EVs go through the cycle until the battery runs out. At the end of a cycle, the average speed is 48.3 mph (77.7 kph).
When the EV’s battery can no longer power the car, the schedule ends and the total distance covered is recorded, becoming the base for what will become the official EPA-rated highway range. Again, more on this further down; it’s one of the two important distinctions that set the EPA rating apart from the WLTP.
Lastly, the EPA conducts the so-called Multi-Cycle City/Highway Test. As with the previous procedures, the battery is fully charged and the car is left overnight before it goes onto the rolling road.
For this test, the vehicle is driven over successive city, highway, and steady-state cycles until the battery is discharged and the car can no longer follow the driving cycle. During the entire test, the EPA monitors and records DC discharge energy and DC discharge amp-hours.
After the test is completed, the battery is recharged to a 100% charge using the manufacturer’s recommended AC charger. Then, the energy consumption of the city and highway cycles is mathematically calculated from the recharging energy, the DC discharge data, and the distance for each cycle.
The big difference between the EPA and WLPT range ratings
With this being said, there’s one more step that the EPA goes through before settling on the energy consumption and range figures that appear on the window sticker. The federal agency says that regulations require that these figures be adjusted to more accurately reflect the values that drivers can expect to achieve in the real world.
So what happens is the range figure, in the case of fully electric vehicles, is usually multiplied by 0.7, leading to a lower value, while the energy consumption number is divided by 0.7, leading to a higher result. These are the ratings that end up on the window sticker.
As you’ll find out further down in this article, the WLTP rules don’t require this final adjustment, and there are also other factors that lead to higher range figures.
What about plug-in hybrids (PHEVs)?
In the case of PHEVs, the testing procedures are similar but they have to account for the presence of the internal combustion engine.
First, a so-called Charge-Depletion Operation is done, which submits the vehicle to the same single-cycle test as the one used for EVs. The procedure starts with a fully charged battery and ends when the battery is discharged, but because some PHEVs might automatically start their engine, both the electric energy consumption and the gasoline consumption are used to calculate the MPGe values for the charge-depleting operation (using the conversion factor described in the EV section for MPGe).
Then, the PHEV goes through a Charge-Sustaining Operation, which is meant to record the gasoline consumption of the vehicle. It starts with a discharged battery and subjects the vehicle to the usual five-cycle method that any other combustion vehicle has to go through to get certified. The results on the electric side are adjusted in the same way as for EVs.
WLTP explained
Now, let's chat WLTP. It was introduced in 2017 by European Union regulators as a more "realistic" approach compared to the old NEDC (New European Driving Cycle) procedure and is mostly used in Europe, although other countries also use it.
Similar to the EPA procedure, the WLPT subjects cars to a driving cycle that is known as the WLTC-C cycle.
In the case of the WLTP, cars are separated into different classes based on their power-to-mass ratio and maximum speed. The higher these parameters, the higher the speeds the vehicles are subjected to during the driving cycle.
For the fastest and most powerful internal combustion cars, the cycle is divided into four sub-cycles: Low, Medium, High, and Extra High. A complete cycle lasts for 30 minutes during which the vehicle travels 14.4 miles (23.26 km) and reaches a maximum speed of 81.5 mph (131.3 kph). However, the vehicle is also stopped for a cumulative time of 227 seconds (3.7 minutes), and the average speed at the end of the cycle is roughly 31 mph (50 kph).
The sub-cycles are also used for pure electric vehicles, but just like in the case of the EPA testing procedure, EVs go through successive cycles until the battery runs out. Additionally, there are so-called constant segments that are designed to deplete the battery faster and shorten the duration of the test.
The lab temperature is set at 73.4 degrees Fahrenheit (23 degrees Celsius), whereas the EPA has a dynamic temperature.
How the WLTP EV range ratings are created
To determine the driving range and energy consumption of a battery electric vehicle, the procedure is divided into two dynamic and two constant segments, which are interleaved as follows: one (dynamic), two (constant), three (dynamic), and four (constant).
In the dynamic segments, the complete cycle is driven first, followed by an additional run of the City cycle, which is made up of the Low and Medium sub-cycles (see the above graph). Between the dynamic segments, the EV is driven at 62.1 mph (100 kph) to make the battery deplete faster. During the whole procedure, the current and voltage of the traction battery are monitored and recorded. After the EV’s battery is empty, it gets recharged to 100%.
As opposed to combustion vehicles, the addition of a City cycle after a complete driving cycle for EVs increases the driving distance to 19.3 miles (31.1 km) for a single dynamic cycle.
To calculate the combined driving range of an EV, the two full WLT Cycles of Low, Medium, High, and Extra High sub-cycles in dynamic segments one and three are taken into account. Then, the total measured energy content (battery capacity) without charging losses is divided by the electricity consumption from the weighted average of the two full WLT Cycles.
To make things easier, here’s the formula:
Range (km) = usable battery energy (watt-hours) / energy consumption (Wh/km)
The City range is obtained by dividing the same measured energy content by the electricity consumption of the City cycle (that is made of the Low and Medium sub-cycles).
WLTP for PHEVs
When it comes to the electric driving capabilities of PHEVs, the WLTP is rather lenient, as the range specification is calculated just in the City cycle (at Low and Medium speed sub-cycles). This results in rather optimistic driving range numbers, as the vehicle is not subjected to high speeds in all-electric mode, as is the case with the EPA testing procedure.
And that’s it!
The main differences between the EPA and WLTP EV range ratings boil down to the lab temperature and the EPA recording the actual number of miles driven, which is then adjusted by multiplying it by 0.7. By contrast, the WLTP produces its ratings by a more complicated mathematical formula which is not adjusted.
A number of factors including battery health, temperatures, driving styles and more determine your real-world range experience and that isn't always in line with what the test cycles promise. Sometimes it's better, too. As always, your mileage may vary; literally, in this case.
