CAMBRIDGE — Cyclists stopped and stared in disbelief Wednesday as police investigated the death of a 60-year-old man who was killed in a gruesome rush-hour crash with a tractor-trailer while riding his bike through Porter Square.

The death of Bernard Lavins marked the second cyclist fatality since June in a city that prides itself on being bike-friendly, and it served as a grim reminder of riders’ vulnerability as they traverse congested streets filled with large vehicles.

A woman who answered the phone at the Lexington home of Lavins identified herself as his wife and said she had no information about the crash. She confirmed that her husband was a doctor but declined further comment.

Earlier Wednesday, cyclists at the crash scene expressed shock and sadness over Lavins’s death.

“That could be me,’’ said Tom Volkert, who regularly bikes through Porter Square on his way to Kendall Square. “Very easily.’’

The collision happened around 8 a.m. at the intersection of Massachusetts and Somerville avenues, Cambridge police spokesman ­Jeremy Warnick said. In the immediate aftermath, two separate sheets were placed on the street, and a bike could be seen under the cab of a large Ryder tractor-trailer. Two cars and a box truck were in a cordoned-off area behind the tractor-trailer, and debris was scattered on the ground near the sheets.

The area was closed to traffic for hours.

The driver, who was not identified, remained at the scene and cooperated with police.

Middlesex District Attorney Marian T. Ryan’s office, which is investigating, confirmed the identity of Lavins and said the driver of the truck remained at the scene.

Ryan’s office released no information about what may have caused the crash, and authorities did not identify the driver. No criminal charges were announced.

The Ryder truck had decals on its side bearing the name of Mitlitsky Eggs, a company based in Lebanon, Conn. A man who answered the phone at the company’s office declined to comment.

Mitlitsky Eggs reported one prior nonfatal crash in the United States over the last two years and had a satisfactory safety rating as of Tuesday, according to an online Federal Motor Carrier Safety Administration database.

Richard Fries, executive director of the Massachusetts Bicycle Coalition, was biking from Arlington through Cambridge when he arrived at the scene.

“This goes right to your gut,’’ he said.

Joseph Barr, the city’s director of traffic, parking, and transportation, and a regular bike commuter, said the Porter Square intersection has been “a location of concern for some time.’’

“It’s a tragic event,’’ he said. “Everyone here is upset.’’

Barr said the city has proposed a number of safety improvements in the area, including easing southbound traffic on Massachusetts Avenue by creating a single left-turn lane and two through lanes, eliminating the left turn from the Porter Square Shopping Center onto Mass. Ave., and simplifying the traffic signal.

“We know Inman Square and Porter Square as problem locations, and we are working on them,’’ Barr said.

In June, Inman Square was the site of a fatal crash that claimed the life of Amanda Phillips, 27.

City Councilor Craig A. ­Kelley, a cyclist who rides through Porter Square, said the city must find ways to improve the intersection. He noted that officials in Boston installed plastic stanchions at the approach to a busy intersection in the Back Bay after a cyclist was killed there last year. He said the markers force everyone coming into the intersection to heed their surroundings.

“We haven’t figured out how to deal with intersections very well in Cambridge,’’ Kelley said.

Before this year, three cyclists had been killed in Cambridge in the past 15 years. From 2010 through 2014, cyclists in Cambridge were involved in an average of 184 crashes per year, police said. A 2014 report found that the crash rate — the number of crashes per bicycle mile traveled — had declined in recent years.

The city’s 2014 analysis also showed that in most cases, cyclists had just minor injuries or no injuries at all.

The Rev. Laura Everett, a cycling advocate who heads the Massachusetts Council of Churches, said the crash Wednesday demands action.

“There will be more funerals if we do not change our roads,’’ she said.

Matt Rocheleau and Sacha Pfeiffer of the Globe staff contributed to this report. Steve Annear can be reached at steve.annear@globe.com. Follow him on Twitter @steveannear. Travis Andersen can be reached at tandersen@globe.com. Follow him on Twitter @TAGlobe.