The No. 66 bus is packed on a recent weekday afternoon as it starts and stops from Chicago’s West Side to Navy Pier.

The seats and windows creak and rattle just like a regular diesel bus, but no one seems to notice the loud whine of the electric motor that makes it go.

That’s exactly what the Chicago Transit Authority wants. Buses that do not yet pollute the air can run the route with the same reliability as those that do, even when cold weather cuts into battery range.

But to make electric buses work, the CTA has had to go far and spend a lot. It built rapid charging points at both ends of route No. 66 which connect to the bus roofs.

Drivers constantly monitor the batteries to make sure they don’t run out, risking the bus running aground. If they get below 50% charge, they are supposed to top them off with a charger.

“We work through the daily challenges of inclement weather in Chicago,” said Don Hargrove, senior maintenance manager at the garage that is home to most of the authority’s 23 electric buses.

The CTA began experimenting with electric buses in 2014, and has developed a system that Hargrove says will work as the transit authority moves to an all-electric fleet by 2040.

Other transit systems are going through the same process to reduce pollution and combat climate change.

Cold weather is the CTA’s biggest problem. When the temperature drops, the lithium-ion batteries that run the buses are not as efficient and lose range. Most of the energy drained from the batteries goes to keeping the bus interior heated to 70 degrees.

“Every time the bus stops to pick up passengers, drop people off, the doors open,” said Richard Lin, assistant manager of bus equipment engineering. “You have to warm up the new amount of cold air.”

The electric buses have a small diesel engine that heats the interior in extreme temperatures to extend battery range, Lin said. But most of the time the buses use electric coil heaters, like a giant toaster, which can zap batteries. When the CTA bought its buses, more efficient heat pumps weren’t available as an option, he said.

On every 10-mile one-way trip on route no. 66, the electric buses lose approximately 8% of their battery energy. In the winter, they start with about 100 miles of range when fully charged. So after about six one-way trips, the policy says drivers must charge as they fall below 50%.

Normally, the timetable has 10 to 15 minutes built in for charging, and the buses get around 1% of a full charge for every minute they connect.

With enough chargers, the electric buses can run all routes, said Lin. “It’s just a matter of our strategy of putting chargers in the right places, having enough chargers available as we scale up our fleet.”

Currently, the CTA has around 1,900 buses and most run on diesel. The transport system is starting to replace them with electric ones, but the investment is huge. Each electric bus costs about $1.1 million, about $500,000 more than a diesel model.

But after the initial capital outlay for the buses and charging stations, the electric buses are much cheaper to operate. The CTA calculates that it costs $2.01 per mile to run the 40-foot-long electric buses. For a diesel bus, it’s $3.08, and $2.63 per mile for a diesel-electric hybrid.

It will take decades for the authority to recoup its investment in the electric buses, but CTA officials say the cost of electric buses will come down as more are sold.

In Alaska’s capital, Juneau, which has a more temperate climate but winter temperatures can still dip below freezing, officials also have plans for an all-electric bus fleet, though one they got in 2020 has been plagued by mechanical problems.

Capital City Transit has ordered seven electric buses to replace 2010 diesel models, said Rich Ross, operations manager. The new buses are expected to run regular routes due to increased battery capacity, “which was not available when we ordered our first bus,” he said.

Cold winter conditions can still knock 100 miles outside the expected 282-mile range of the new buses, so on the coldest days they can be put on commuter routes that only run during the busiest transit times, Ross said.

Like Chicago, Capital City Transit also plans to build an “in-route” charging station for buses that can be plugged in if they run out.

Back on the No. 66 in Chicago, Dawn Carter, 54, says she’s glad electric buses ply the route because they’re good for the environment.

About the only difference is that the electric buses are quieter than those with clanking diesel engines and noisy heaters, but few people notice that, she says. “When I get to work, everyone’s just rushing to get on and off,” she says. “It’s just quieter. It’s easier to talk to people. When the heat goes on and off, you barely notice it.”