Since modern electric cars went on sale in volume five years ago, some cities have been more eager to promote them than others.

Officials in those cities find electric cars attractive for their ability to reduce pollution,among other reasons.

And those officials do everything from expanding charging infrastructure to implementing incentives like free parking in order to get more electric cars' on their cities streets.

DON'T MISS: Top 10 Cities For Electric Cars: San Francisco Leads, But It's Not All California (Mar 2015)

But which city does it the best?

Researchers at the Indiana University School of Public and Environmental Affairs recently compiled a list of the most electric-car-friendly U.S. cities (via Charged EVs).

Portland, Oregon, was at the top of that list, which includes 36 cities.

PowerPost Level 1 electric-car charging stations at Portland International Airport

PowerPost Level 1 electric-car charging stations at Portland International Airport

The city has a generous network of charging stations, including a block of parking spaces reserved for plug-in cars that is known as Electric Avenue.

It also streamlined the process for installing home charging stations.

And Portland's policies are backed by a state government that's also enthusiastic about electric cars.

ALSO SEE: Portland's Electric Avenue Relocates, Adds DC Fast Chargers (Jul 2015)

Oregon is the only state to have appointed an Electric Car Czar, and it participates in the West Coast Electric Highway project to create a network of charging stations linking the West Coast states.

The state also offers tax credits for the purchase of charging stations, including a $750 credit for individuals, and a credit for businesses that covers 35 percent of the cost of a station.

Portland was followed by Washington, D.C., Baltimore, New York City, and Denver on the Indiana University list.

Electric Avenue rededication, Portland, July 2015

Electric Avenue rededication, Portland, July 2015

Los Angeles, Atlanta, Chicago, Austin, and San Francisco rounded out the top 10.

Columbus, Ohio, was at the bottom in terms of electric-car friendliness.

MORE: West Coast Mayors Form EV Consortium, Pledge Carbon Reductions (Dec 2015)

Cities were ranked based on factors like the availability of purchase incentives, charging-station density, and perks like free parking or solo carpool-lane access.

Four of the top six cities also offer time-of-use electricity rates, while others provide at least some free parking.

Nashville—the largest city near Nissan's U.S. headquarters—offers free parking in its downtown area, while Honolulu exempts electric-car drivers from all parking fees.

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