Aurich Lawson | Getty Images
How does the US Environmental Protection Agency decide how far an electric vehicle can go on a single charge? The simple explanation is that an EV is driven until the battery runs flat, providing the number that goes on the window sticker. In practice, it’s a lot more complicated than that, with varying test cycles, real-world simulations, and more variables than a book of Mad Libs, all in an effort to give you a number that you can count on to be consistent and comparable with other vehicles on the road.
The start of EPA mileage testing
The EPA started testing vehicle fuel economy in 1971, and that initial testing still plays a major role in how modern cars are measured.
The year before, President Richard Nixon signed the National Environmental Policy Act of 1969 (followed by the Clean Air Act of 1970) and established the EPA with a mandate that included lowering motor vehicle emissions. Part of the EPA’s plan to reduce emissions was to let buyers know just how much fuel a car would use so they could cross-shop cars effectively.
Testing started with a route called the Federal Test Procedure. The EPA adopted an 11-mile (18-km) route that was originally done on real roads in Los Angeles. The route had an average speed of 21 miles per hour (34 km/h) and a top speed of 56 mph (90 km/h). Tailpipe emissions were measured, fuel economy was calculated, and the “city” fuel economy rating was born.
By the time the 10-mile (16-km) Highway Fuel Economy Test was added in 1974, the tests were performed in a lab on a dynamometer. Running tests on the dyno made them more consistent and easier to repeat, though it wasn’t perfect.
Small changes and tweaks were made over the years, with the biggest change announced in 2005. That year, the EPA announced changes to the test to meet new highway speeds, account for heating and air conditioning use, and make the test more relevant to real-world driving. Drivers weren’t able to hit the published numbers, and the EPA wanted to fix that. The system was introduced for the 2008 model year and is largely the one we use today.
Modern range testing
Today, automakers have two different test options for EVs. The automaker can decide that it wants to perform a “single cycle” test. On that test, the car drives the EPA city cycle over and over again until the charge runs out, then does the same on the highway cycle, starting with a full charge. The process is repeated for reliability. The alternative is that the automaker can perform a multi-cycle test that has completed four city cycles, two highway cycles, and two constant speed cycles.
The test cycles
The city cycle
The EPA’s Urban Dynamometer Driving Schedule is the official “city cycle” test loop. It is a complicated graph of time, vehicle speed, and allowable acceleration. The total test time is 1,369 seconds, the distance simulated is 7.45 miles (12 km), and the average speed is 19.59 mph (32.11 km/h). As with all of the tests, the exact speed required at each second of the test is laid out in a spreadsheet.
The highest speed reached on the test is 56.7 mph (91.25 km/h), and there are several periods where the vehicle sits stationary. Stationary seconds of the test made more sense when it was designed to measure a gas vehicle’s idle emissions and consumption, but it does still have some relevance today when it comes to climate control use and energy required to accelerate the vehicle.
The highway cycle
For higher speeds, vehicles complete the Highway Fuel Economy Driving Schedule (HFEDS). This test has a top speed of 59.9 mph (96.4 km/h) and an average of 48.3 mph (77.73 km/h), and it takes 765 seconds to complete.
Only the UDDS and HFEDS tests are required to certify an EV. But a top speed of 59.9 mph is a much lower highway speed than most drivers will experience.
Driving more quickly or using climate control can greatly impact range. More tests were introduced to help give a more realistic range, and they’re part of the 5-cycle test covered below.
Source link
