TriMet, doubling down on its expensive Washington County commuter-rail service, wants to buy two new railcars from a Texas transit agency.

The agency's board will be asked Wednesday to authorize paying Dallas Area Rapid Transit up to $1.5 million for the diesel-powered cars. They would serve TriMet's Westside Express Service, a heavy-rail line that runs between Wilsonville and Beaverton during the rush hour.

The agency would also have to pay $500,000 to refit the cars.

The agency cites "expected demands for the growing WES service," even though ridership on WES has been slipping for the last 2 1/2 years -- and it wasn't all that high to begin with.

Weekly trips peaked at 10,700 in October 2013, and the count has held steady just above 9,000 in the last year. The Orange Line, the least busy MAX light-rail line, gives more rides in an average weekday than WES does in a week.

TriMet spokeswoman Mary Fetsch said in an email that the slump in ridership reflects low gas prices.

"Conversely, when we see high gas prices, we see ridership increase," Fetsch wrote. "We need to plan for ridership growth."

While a fare for WES costs the same as a bus or MAX train, the commuter rail service costs TriMet much more -- about $15 in fuel, labor and maintenance costs per rider.

A bus ride, on the other hand, costs TriMet about $3 per rider, while the operational cost of MAX is around $2.50 per rider.

TriMet said the purchase would allow for extra trains to swap into service when another is in the shop, in addition to facilitating ridership growth. It said planned repairs in 2017 would take cars out of service for up to three weeks at a time.

TriMet would be getting a deal on the used cars compared to some of its previous attempts to bolster its fleet.

In 2014, it sought to buy two new cars from a original manufacturer for $7 million, using an option held by Sonoma-Marin Area Rapid Transit in California. The manufacturer, however, wouldn't honor the price for TriMet. Later, manufacturer U.S. Railcar quoted a price of $10 million for two new cars. TriMet also offered $750,000 for two cars for sale when a Canadian train refurbishing firm went out of business, but was outbid.

In 2009, TriMet paid $150,000 for a pair of 56-year-old Alaska Railroad cars to use as spares.

Its fleet currently includes a total of six cars.

-- Elliot Njus

enjus@oregonian.com

503-294-5034

@enjus