Streetcars? Why not electric trolley buses?

That question popped up Tuesday as Seattle City Council members were briefed on four possible streetcar routes to extend the system now only in South Lake Union.

Prompting the discussion were money concerns.

City transportation department officials told council members the most promising streetcar extensions would be north to the University District, Fremont and Ballard, and south to Pioneer Square and east to the International District and Capitol Hill.

Total estimated construction cost: $599 million, in 2010 dollars, not including the cost of running each line each year.

Councilman Tom Rasmussen, a skeptic about streetcars, said electric trolleys may be a better deal.

He cited other cost estimates from city transportation officials showing that streetcars cost three to six times as much to build as electric trolley buses. Both are powered by electric wires, but fixed rails must be built and maintained for streetcars, while rubber-tired trolley buses run on street pavement without tracks.

According to the city estimate, electric trolley construction and facilities such as power lines would cost $7 million to $8 million per mile for systems lasting 30 years. The city estimate compared that to $30 million to $45 million per mile for streetcar systems that last 40 years (one proposed line would cost more than $50 million per mile). Light rail trains, by comparison, cost between $100 million and $160 million per mile and can last more than 60 years.