Traffic jams made the 42-year-old Foxborough native anxious. Sullivan couldn’t go into a crowded mall. And he was haunted by the memory of a man who approached him while he was working to disable an improvised explosive device during one of two deployments to Afghanistan, he said. Sullivan faced a choice: Shoot, or risk that the man was a suicide bomber. He didn’t fire, but the stress stuck with him.

Last year, Sullivan, who now lives in Virginia, began using a smartphone application developed by the Department of Defense to guide him through breathing exercises when his anxiety began to build. The same agency launched another app earlier this year for veterans to use while in a particular kind of therapy, revisiting difficult memories with a professional. Sullivan became curious, and this summer returned to treatment.

Ten years ago, the resources available to veterans with PTSD who were unwilling or unable, because of geography or other factors, to be treated by a therapist were limited. Researchers are developing technologies to reach people like Sullivan wherever they are, putting tools directly into their hands through programs online and on their smartphones.

Studies suggest that helping veterans and others early on in their experience with trauma-related stress may prevent some of the more catastrophic effects of PTSD. That requires giving people who aren’t sure whether their symptoms are severe enough to warrant attention from a doctor — or don’t want to admit it — a safe route to learn more. And it means finding effective ways to treat the large numbers of service members who have experienced war-related trauma in the past decade.

As many as one in five people who have served in Iraq and Afghanistan may have symptoms of PTSD or major depression, according to a 2008 RAND Corporation study. Only about half of the people with symptoms sought mental health care in the year before they were surveyed.

Treatment for PTSD historically has taken a one-on-one approach, with some small group therapy, said Terence M. Keane, who directs a division of the Department of Veterans Affairs National Center for PTSD that is based in Boston and focused on behavioral science.

Keane and others began thinking a decade ago about how to use the Internet to provide behavioral health care to the masses. In 2009, the National Institute of Alcohol Abuse and Alcoholism awarded researchers at the VA and the medical and public health schools at Boston University $909,000 in stimulus money to study an online treatment to see if it would ease the effects of trauma and reduce risky drinking in veterans.

The researchers recruited 600 people using targeted Facebook advertisements on pages for veterans of the wars in Iraq and Afghanistan. The ads attracted people in major cities, in rural parts of Idaho, Montana, and North Dakota, and elsewhere. The program was as anonymous as researchers could make it. Participants provided an e-mail address but no name.

About two-thirds immediately started an eight-part program to evaluate their drinking, identify triggers of PTSD symptoms, and find ways to cope that did not involve alcohol. The others started the same program two months later.

The first group reported a greater reduction in PTSD symptoms and drinking than the group waiting for access to the program. The drop in alcohol intake continued three months after the program ended.

The online format can reach many people at once, Keane said, while anonymity could attract those who may not otherwise seek help. Often, people who come to the VA for therapy have lost jobs or spouses as a result of their PTSD, alcohol use, or other behavioral health issues. “That’s the end of the continuum,” Keane said. “We’re trying to get to people way before then to prevent a lot of things from going wrong.”

Keane has presented the results, which are not yet published, at several conferences this year. Now, he is searching for grants from foundations and others to reopen the program, at VetChange.org . He is hoping to develop similar programs for people who have PTSD and physical injuries, chronic pain, or other addictions.