Philadelphia won't move faster on a number of upgrades to make biking safer in the city, according to a letter from the mayor's office to the city's lead cycling advocacy group.

Mayor Kenney's letter was a response to a request from the Bicycle Coalition of Greater Philadelphia to speed up infrastructure improvements and devote more money to street safety initiatives.

The mayor's letter showed a commitment to street safety initiatives, said Sarah Clark Stuart, the coalition's chief executive, but she was frustrated that action would not come more quickly.

"I'm disappointed that at this point in time they're not going to be able to increase resources, but we can continue to ask," she said.

Urgency needs to be tempered with coordination, Kenney wrote in the letter, and advocates need to recognize the city's financial limitations. Data gathering and consensus building, the mayor wrote, "will lead to broad, citywide consideration of the factors contributing to traffic-related fatalities, and the measures the city can take to have the greatest effect in terms of protecting lives."

The mayor declined to commit additional money to the city's street safety program, Vision Zero, saying the city's finances "remain particularly vulnerable over the next few years." The Streets Department has $1 million dedicated to Vision Zero and the Office of Transportation and Infrastructure Systems an additional $500,000. The Bicycle Coalition asked for an additional $1 million.

City officials have discussed the caution needed when changing a street's infrastructure. Along with some street upgrades needing City Council approval, city officials also must navigate controversy that can accompany bicycle infrastructure improvements, which in some cases reduce automobile travel lanes and parking options. Because of this, the city won't release a comprehensive, citywide plan for the 30 additional miles of protected bicycle lanes the mayor has pledged. Instead, the city will announce projects one at a time, the letter stated.

"Going into this, we understood that we are part of the equation, and the public and City Council are the other part," said Michael Carroll, the city's deputy managing director for the Office of Transportation and Infrastructure Systems. "We always get into trouble when we make decisions we don't have full authority for."

Cycling advocates have sought a clear vision from the city of where on the city's 200-mile network of bike lanes protections would be added. Philadelphia has stated street safety goes beyond bikers, with pedestrians and drivers also likely to benefit from street redesigns and upgrades. About 100 people a year die in the city in auto-related crashes.

"If you're not planning for what you're going to do in the future, how are you ever going to get it done when you get there?" asked Victoria Maciunas, a trained urban planner and frequent cyclist.

The lack of a plan shows a lack of leadership, she said, and sends the message that "the city doesn't have more power than its grumpiest neighbors."

The city, again citing the need for community cooperation, also resisted a call for a new infrastructure plan on Spruce and Pine Streets, two of the busiest bike routes in the city, within the next three months.

"Too often, residents are pitted against bike lane supporters," the mayor wrote. "If we want to see meaningful expansion of bike lanes across the city, that intense tension must end."

He also noted those streets are not among the most dangerous in the city, something that is a consideration due to limited resources.

The city, though, will review proposals to improve visibility at intersections along those two busy streets, the mayor wrote, and look at ways to create a schedule for lane and crosswalk painting that wasn't linked to repaving. Kenney's letter highlighted the improvements that have come in 2017, including a protected bicycle lane on Chestnut Street in University City, five miles of new bike lanes, and another 11 miles of bike lane upgrades.

Concerns over bicycle safety have prompted a series of protests in the city, the most recent on Tuesday. Dozens of people lined 13th Street in Center City and formed a human barrier between the cycling and driving lanes.

The dangers big trucks pose on city streets is one issue getting attention. In the past month one cyclist was killed and another badly injured in crashes with trucks on city streets. The most recent, Becca Refford, survived after colliding with a truck on the 1200 block of Pine Street Friday. A truck had been making a right turn from 13th Street onto Pine, which does have a bike lane, when it hit her. The driver is cooperating with the investigation, authorities said.

Refford recalled falling and getting trapped beneath the truck's rear wheels on the 1200 block of Pine, crushing her legs, she said in an interview. She suffered a fractured pelvis and shattered hips.

Refford's accident occurred less than three weeks after Emily Fredricks, a 24-year-old pastry chef, was killed in a bike lane on 11th Street on her way to work.

Half of all cyclists and a quarter of pedestrians who die in a crash involving a large truck hit the side of the vehicle, the federal Department of Transportation reported. Some American cities, including New York City and Boston, have passed ordinances to require some truck companies to add side guards between the front and rear wheels to keep people from falling into the space.

The Boston ordinance, passed in 2014, requires the city to contract only with vendors that have side guards installed on all trucks more than 10,000 pounds and semitrailers with a total weight exceeding 26,000 pounds. The side guards cost about $850 per vehicle, the ordinance states. There are also requirements that trucks have mirrors that reduce blind spots.

The city is experimenting with adding side guards on big truck purchases, Carroll said, starting with the Streets Department. It wasn't clear Tuesday how many vehicles would be affected, but the city has 330 trash trucks that would be candidates to have side guards installed, said city spokesman Mike Dunn. The side guards need to be tested, city officials said, and the project will likely take several years. There are 12 new garbage trucks slated to be purchased, officials said.

The city's three-year Vision Zero plan includes prioritizing contracting with companies with side guards on a percentage of their trucks.

Online shopping has played a role in boosting the number of trucks in Philadelphia, with 18,000 deliveries and pickups taking place each day in Center City's four main zip codes. An additional 2,500 trucks are in the city each day providing services. With many of these trucks traveling on private business, it's unlikely an ordinance like Boston's would require shipping companies to upgrade their vehicles.