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Over the past year, Traffic Lab received hundreds of thoughtful and compelling questions about transportation from our readers.

Here’s a roundup of some of our favorites submitted as part of our series of Q & As.

If you have a question or idea for Traffic Lab as we head into our third year, send it to trafficlab@seattletimes.com. We may feature it in an upcoming column.

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 and Seattle Children’s hospital. Seattle Times editors and reporters operate independently of our funders and maintain editorial control over Traffic Lab content.

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Q: Why do King County Metro buses sometimes run one right behind the other?

A: It’s never intentional. The agency doesn’t schedule buses heading toward the same destination to arrive together, and purposefully builds routes to prevent bunching, said Metro spokesman Jeff Switzer.

When it does happen, it’s usually because of traffic congestion, construction, overcrowding, boarding delays or variations in driver style. Read more.

Q: Why doesn’t Sound Transit use turnstiles at light-rail stations?

A: Sound Transit uses a proof-of-payment system, where instead of turnstiles, enforcement officers check passengers once they are on board, because that is less costly, more effective at preventing fare evaders and inherently safer than gateway entrances, said agency spokesman Geoff Patrick. Read more.

Q: How does the city decide when and where to grant developers street-use permits for construction projects, particularly when the building is along a main thoroughfare?

A: The Seattle Department of Transportation (SDOT) considers several factors in granting permits. They include public safety, the impact of any proposed street closures, whether sidewalks can remain open on the same block, and the ability to build while minimizing disruption. SDOT also considers the effect of construction during peak commute times, said spokesman Norm Mah. The agency does not allow sidewalks on both sides of a street to be closed. Read more.

Q: When and where are bicyclists allowed on sidewalks in Seattle?

A: Bicyclists can ride on any sidewalk in Seattle as long as they do so in a “careful and prudent manner.” However, they must yield the right of way to pedestrians, just as drivers are supposed to yield to pedestrians and bicyclistsRead more.

Q: What does Washington state do about newcomers who keep out-of-state license plates?

A: New residents are supposed to pay a whole set of fees and get new license plates when they bring a car to Washington. But that doesn’t always happen. Law enforcement can cite newcomers who fail to register their cars on time. But officers aren’t on the lookout for violators, so the scofflaws usually get caught when pulled over for another infraction. Read more.

Q: How does the state deal with abandoned cars along Washington freeways?

A: What happens to an abandoned car depends on where it’s been left.

If a car is in a designated tow-away zone, the State Patrol will impound it. Troopers will also have the vehicle towed if it’s too close to the fog line or on the left side — usually the faster side — of the freeway and causing a distraction or danger for motorists.

Cars left elsewhere are tagged with a ribbon tied to the antenna as a cue to other troopers that the vehicle has been marked. The car is entered into a state tracking system and the owner has 24 hours from that time to retrieve it before it’s towed. Read more.

Q: Can drivers cut through alleys to sidestep traffic?

A: Yes, unless the alley is signed otherwise. It is also legal to walk through alleys unless signed otherwise. Read more.

Q: What’s the rule on angled parking in Seattle?

A: Vehicles parked in angled spots must be positioned in a direction “consistent with such markings or signs,” according to the Seattle Municipal Code. It is only illegal to park with the front of a car facing the curb when a nearby sign says “Back-In Angle Parking Only.” Vice versa for a “head-in parking” sign. The ordinance is for safety reasons. Read more.

Q: Why are empty buses that are “out of service” or “returning to terminal” allowed to use the carpool lane?

A: Allowing buses, even when empty, to use carpool lanes keeps them “moving to where they need to be” in order to “carry the most people possible, which also takes cars off the road that might otherwise be there,” Switzer said.

Sometimes bus drivers are heading from the base to a starting point for a trip and use the freeway to get there quickly and efficiently, he said.

Other times, such as when the bus is out of service, a driver may have just completed all of his or her trips or finished a shift and is returning to base on the fastest route possible. Read more.

Q: What are drivers who park on the street supposed to do when they go on vacation for a week?

A: Seattle’s municipal code does not permit vehicles to be parked on a city street for more than 72 hours — three days — without being moved. According to SDOT’s website, “If you are going on vacation, find off street parking or leave your keys with a trusted neighbor to check your vehicle and move it as needed.” Read more.