Since The Seattle Times Traffic Lab launched a year ago, we've heard from scores of readers about getting around. You've responded when we've asked for stories of your commutes, and you've asked us thoughtful and compelling questions about the city's thorny transportation issues.

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Navigating the streets and sidewalks of Seattle can be a challenge.

There are signs, signals and sounds to understand, new laws to obey and people — driving cars, riding bicycles, walking, e-riding — to watch out for.

Since The Seattle Times Traffic Lab launched a year ago, we’ve heard from scores of readers about getting around. You’ve responded when we’ve asked for stories of your commutes, and you’ve asked us thoughtful and compelling questions about the city’s thorny transportation issues.

Traffic Lab is a Seattle Times project that digs into the region’s thorny transportation issues, spotlights promising approaches to easing gridlock, and helps readers find the best ways to get around. It is funded with the help of community sponsors Alaska Airlines, CenturyLink, Kemper Development Co., NHL Seattle, PEMCO Mutual Insurance Company, Sabey Corp., Seattle Children’s hospital and Ste. Michelle Wine Estates. Seattle Times editors and reporters operate independently of our funders and maintain editorial control over Traffic Lab content.

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If you have a question or idea for Traffic Lab, send it to trafficlab@seattletimes.com. We may feature it in an upcoming column.

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If you need to brush up first, here’s a roundup of some of the most interesting questions from the past year as part of our Traffic Lab series of Q & As.

Q: With thousands of pedestrians roaming Seattle’s Pike Place at the historic market, why are vehicles allowed on the street?

A: The market’s hundreds of vendors and businesses need easy access to their stalls, shops and restaurants for transporting goods, said Emily Crawford, a spokeswoman for the Pike Place Market Preservation & Development Authority. Some vendors also park their cars or trucks on the road and use them for storage. Read more.

Q: Who would be responsible if a self-driving car crashes?

A: In Washington state, as of now, there’s no clear answer. And there really isn’t much of an answer anywhere else, either.

Scholars and experts in the field tend to have two  general assumptions: Widespread use of self-driving cars will mean fewer collisions, and there will be some shifting of liability from drivers to manufacturers.

States are generally responsible for establishing liability and insurance rules, and the federal government’s guidance on self-driving cars, released last year, put the onus on the states. Read more.

Q: Do pedestrian push-to-walk buttons do anything?

A: Most walk signs in downtown and other dense areas activate on a timed schedule, regardless of whether someone hits a button. Others require a tap to change the pedestrian signal. The thing is, there’s no foolproof way to tell which is which. Read more.

Q: When and how do Seattle’s dangerous sidewalks get fixed?

A: Landowners are responsible for taking care of sidewalks and planting strips next to their properties. They should mend cracks and other damage, as well as remove safety hazards, such as ice and snow, per the Seattle Municipal Code.

Same goes for keeping paths clear of overgrown trees and bushes, unless they are city-owned, as well as picking up garbage. Read more.

Q: How does Metro Transit determine whether a bus is running on time?

A: Metro gives buses a seven-minute window to show up to still be considered “on time.” That window runs from 1.5 minutes early to 5.5 minutes late. Show up anytime in there with room for passengers, and the bus counts as on time.

Over the last 12 months, regular Metro buses have been “on time” 77 percent of the time. That figure has stayed fairly consistent over the past five years, as Metro has met the growing demands of booming ridership and stifling traffic congestion by adding more service hours, giving buses priority in their own lanes and at traffic lights, and investing in a newer bus fleet. Read more.

Q: If tech giants like Amazon add to Seattle traffic congestion, do they pay to help relieve it?

A: When developers submit permit applications for construction, officials review how their projects will impact transit, drivers, pedestrians and bicyclists in the surrounding area.

Then, officials require those applicants to directly pay for infrastructure projects or make payments through the Seattle Department of Transportation for future improvements. Such mitigation payments are aimed at reducing the development’s effect on transportation. Read more.

Q: Do Uber and Lyft worsen Seattle’s traffic congestion?

A: A study in New York City said the growth of the app-based ride services could work against cities’ goals of unclogging streets and reducing vehicle emissions, as well as potentially undermining other transportation options, such as public transit and taxi services.

Uber and Lyft dispute the New York report’s findings, pointing to the companies’ service of taking people to and from transit stations, for instance, and their support for proposals to grow public transportation.

According to University of Washington professor and traffic expert Mark Hallenbeck, Seattle’s dense neighborhoods have more at stake in terms of how the app-based services clog roads. People in those areas rely more on the companies compared with those in the suburbs — to evade parking hassles, for example. Read more.

Q: As park-and-rides overflow, would building more parking boost transit ridership?

A: According to King County Metro officials and experts, the correlation is not so simple. And considering the price of building new parking, they say there are more desirable ways to maximize space and improve transit access. New parking stalls can cost $30,000 to $75,000 each to build,  and a proposed Sound Transit park-and-ride in Kent could top $100,000 per stall.

Doubling the system’s current park-and-ride capacity, which includes about 25,000 spots at 137 sites, for instance, would cost $615 million. Ridership, in turn, would increase by less than 5 percent, Metro says. Read more.

Q: Who’s responsible for cleaning Metro bus stops, and how often do they do it?

A: Crews with the Metro Transit Power and Facilities Section rotate around the region’s some 1,700 bus shelters with power washers and other equipment for scrubbing graffiti, cleaning benches and picking up garbage, Metro spokesman Scott Gutierrez said. Volunteers, on the other hand, take care of trash around the bus stops.

Metro’s crews prioritize shelters based on ridership. The more popular the route, the more regular the cleaning. Shelters in downtown Seattle get washed seven days a week, while others across the county get cleaned at least once a week, Gutierrez said.

Riders can report dirty or problematic bus shelters to Metro’s hotline, 206-477-3850. The agency will then send someone out to take care of it, Gutierrez said. Read more.

Q: How do Metro and Sound Transit decide whether to add extra buses before and after major Seattle sporting events?

A: Officials weigh factors such as expected crowd size and if attendees have access to other transit options. They also weigh logistic issues in arranging bus drivers’ schedules and shuffling vehicles around.

“Anytime there is an event that draws large crowds or is expected to have significant impacts on transit service, Metro will more often than not add extra service or some type of mitigation,” Gutierrez said in an email.

At Husky Stadium, the University of Washington has hired extra Metro buses to work as park-and-ride shuttles. The Seahawks have done the same at CenturyLink, Gutierrez said. Read more.

Got a question?

If you have a question or idea for Traffic Lab, send it to trafficlab@seattletimes.com. We may feature it in an upcoming column.

Staff reporters Jessica Lee, Mike Lindblom and David Gutman contributed to this story.