Metro has experienced a sharp increase in arcing events since last summer. They were a large part of the agency’s long SafeTrack rehabilitation project. (Michael S. Williamson/The Washington Post)

Electrical arcing incidents — which can lead to track fires — have more than doubled on Metro since last summer — a spike that undermines the agency's contention that safety and reliability are improving.

Arcing happens when stray electrical current from the track's third rail finds an alternate path to the ground, usually because of dirt, mud or puddled water.

Between July and September, there were 19 arcing events. During the same period in 2016, there were nine such incidents, according to a safety report released Monday by Metro, covering the first three months of the fiscal year that began July 1.

The sharp increase in arcing events — with their sometimes dramatic displays of smoke, sparks and fire — is particularly concerning because they were a big part of the reason for the agency's year-long SafeTrack rehabilitation program.

The uptick in incidents is happening at a time when agency officials are trying to make the case that the system has gotten safer in the two years since General Manager Paul J. Wiedefeld was brought on and safety oversight was handed to the federal government. Metro board member Robert Lauby, vice chairman of the panel's safety committee, said he was concerned about the sharp rise.

"We're hoping that there's a way to get this problem under control," Lauby said.

Since the end of SafeTrack in June, some types of track fires have decreased, including those caused when trash, tree branches, abandoned pieces of equipment or other debris come into contact with the electrified third rail. There were 11 of those fires in the three-month period this past summer, down 39 percent from summer 2016.

Metro safety officials say the sharp increase in events is probably a product of water leaking into underground tunnels. Several of the arcing incidents this past summer happened at or near the Woodley Park and Medical Center stations, at either end of a stretch of the Red Line tunnel that has been prone to water infiltration since it was constructed.

Metro has struggled for years to contain leakage in this part of the system, with limited success. Maintenance workers cleared out drains and made tunnel repairs during SafeTrack, but those improvements were modest, and Wiedefeld said that part of the system needs more aggressive treatment.

Last summer, Wiedefeld commissioned a short-term exploratory project to test the effectiveness of an experimental strategy that involves drilling hundreds of holes into tunnel walls and injecting them with a sealant that drips down and covers the porous concrete in a waterproof membrane.

Wiedefeld says the agency has had preliminary success with the project and is launching a second run of test trials to better determine whether it would be worthwhile to embark on a larger project that would extend the same strategy over the entire leak-prone stretch of the tunnel.

But expanding the pilot would be expensive and take money that Metro, at least now, doesn't have.

"It seems to have worked pretty well," Lauby said. "And if it's going to work and keep the tunnels drier, then that's probably an investment that needs to be made."

Nine of this past summer's arcing incidents occurred in July, a month, Metro points out in the report, when the Washington area had nine inches of rain. (Average precipitation for July is 3.5 inches, Metro said.)

"If you look at the records, a lot of the incidents seem to follow days when we got a lot of rain," said Lauby, who is chief safety officer at the Federal Railroad Administration. "All that water has got to go somewhere, and it ends up down in the tunnel, and it seems like it really aggravates the arcing incidents."

Lauby said he has asked Metro for details on what the agency is doing to address the increase, and how quickly it expects to bring the problem under control.

According to the report, there also were a larger-than-normal number of arcing incidents at the Rosslyn station during the time covered in the report. Those incidents were also because of water intrusion, Metro said. And there were two, more serious, electrical cable fires on the system between July and September, one more than in the same period last year.

The increase in arcing incidents and cable fires resulted in a rise in the overall number of fires, which went up 14 percent from summer 2016.

The increase in track fires came amid improvements in safety and reliability, according to the report.

Offloads — when passengers are forced to deboard a train experiencing mechanical problems — were down 45 percent, which Metro attributed to increased reliability and the retirement of the problematic 1000- and 4000-series trains.

And from July to September, there was just one red signal overrun, when a train operator shoots past a red signal instead of stopping.

There were seven such incidents between July and September 2016, including near misses that endangered the lives of passengers or workers.

Metro officials say they've gotten the signal overrun problem under control, in part by retraining train operators, installing bright LED lighting and modifying train cab consoles to add steps that operators must take to bypass red lights.

Still, other significant safety issues remain.

The rate of passenger injuries increased — up 5 percent for rail passengers and 22 percent for bus riders. Most of the injuries on trains or in stations were trips, slips and falls. The largest number of bus injuries resulted from collisions — in particular, an August event in which a bus hit a defective steel plate intended to cover a hole during road construction in Chinatown, resulting in eight passenger injuries.