A Melrose woman who took a trip to the Vineyard for the day with her husband, friends and young family, was killed in a grisly accident on Tuesday afternoon when she fell from her bike on State Road in Vineyard Haven into the path of an oncoming tractor trailer.

Dina Dececca, 40, was pronounced dead at the scene on State Road near Camp street, about a block west of the head of Main street, Vineyard Haven just past the Martha’s Vineyard Savings Bank. The time of the accident was just after 2 p.m. The 18-wheeler that struck her is owned by the E.C. Cottle Company and had just come off a Steamship Authority ferry. The driver and sole occupant of the truck was Bruce O’Donnell, 46, of Oak Bluffs. Massachusetts state police said they expect no charges to be filed in the incident, which is being described as purely an accident, where the cyclist apparently lost her balance and fell as the tractor trailer was climbing the slight hill headed out of Vineyard Haven. Both the cyclist and the truck were traveling in the same direction. Police said Ms. Dececca, who went under the flatbed portion of the tractor trailer, was wearing a helmet.

Traffic conditions were congested at the time on a sweltering summer day with temperatures in the high 90s. State Road was closed for about three hours while police attended to the scene, causing huge traffic backups in all directions until late in the afternoon.

In addition to state police, Tisbury police and volunteer firefighters also responded. The state police accident reconstruction team and a separate truck team traveled to the Island from the mainland to begin an investigation, which remains ongoing, into the accident.

There were a number of bystanders who saw the accident, and all were badly shaken. Police said Ms. Dececca was in a group of nine cyclists that included her husband and two daughters, aged 10 and 7. The group reportedly had traveled to Martha’s Vineyard for the day from Falmouth, where they were renting a house for a summer vacation.

Following the accident reader comments poured onto Web sites that posted the news, most of them heartfelt expressions of shock and sympathy for the family.

“We are all struggling to explain this terrible tragedy to our children,” wrote one Melrose resident to the Melrose Free Press on Wednesday.

“I weep,” Christopher Gray, a longtime seasonal resident of Vineyard Haven, wrote in a letter to the editor of the Gazette that is published in today’s edition.

According to the Melrose Free Press, Ms. Dececca had worked for the last six years as a manager at Turner’s Seafood Grill and Market. “She had a beautiful, warm smile,” a coworker told the newspaper.

Her death marks the sixth bicycle fatality on the Vineyard since 1987.

Funeral arrangements, under the care of the Gately Funeral Home in Melrose, were incomplete at press time.

But other bits and pieces about Dina Dececca’s life collected from the Internet showed her to be a person who was widely civic-minded and cared about others.

She was a volunteer and member of the board of directors for The Bridge, a community school partnership in Melrose.

She ran in the Andrews Run and Family Day Four-Miler in Wakefield in 1996.

She walked in the Avon Walk for Breast Cancer in Boston this year, a member of an all-women team that called themselves Teachers for Ta-Tas. “Our name may be a little funny, but our mission is a serious one. “We are all teachers — whether it’s by profession, the fact that we are parents or simply our desire to educate people about the fight against breast cancer,” the women wrote on the Avon Walk for Breast Cancer Web site.

She posted an expression of sympathy online when one of her customers at the restaurant, Maurice H. Glazier, died in February of this year.

“So sorry to hear about Mr. Glazier. He was a favorite to us at Turners in Melrose. He will be sorely missed,” she wrote.