With some basic math, this week’s column tackles that question, as well as highlights some rules for park-and-ride lots.

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Are buses in Seattle too heavy? Is that why some streets are so beat up?

Some basic math can help answer.

We break down the bus-weight issue in this week’s Traffic Lab Q&A, as well as highlight some rules for King County Metro Transit’s park-and-ride lots.

You know the drill:

 

Q: It seems to me that Seattle arterials with bus routes have more pot holes and ruts than other roads. Do buses that regularly use Seattle streets exceed allowed weight limits? If so, is the city reimbursed by King County Metro Transit for the damage caused?

— Tim Dobler, Seattle

A: Nationwide regulations set weight limits for transit buses to, in part, protect roads and bridges from deteriorating. That weight, as well as pavement design and the number of buses on a particular route, can impact wear and tear on roads.

Get your scratch paper ready.

For buses, the standard legal weight limit is 10 tons per axle, according to a spokesman for the Seattle Department of Transportation (SDOT). Metro’s 40-foot-long coaches have two axles, while the 60-foot-long buses have three.

That adds up to maximum allowable weights of 20 tons and 30 tons, respectively.

According to a Metro spokesman, buses around here fall within that range. A 2004 study by Spokane engineers found that when full, 40-foot buses like Metro’s weigh about 18 tons. And most longer ones, also while full, weigh roughly 26 tons, the study showed.

For perspective, that maximum weight is about 15 times that of a midsize car.

As for the payment issue, Seattle doesn’t charge Metro for using its streets.

But SDOT and Metro do partner while mapping out road improvements under big funding packages, such as the $930 million Move Seattle Levy. Voters in 2015 approved that proposal, which includes numerous street and bridge-maintenance projects.

As part of a big construction project started in 2015, crews rebuilt a crumbling stretch of 23rd Avenue in Seattle’s Central District, a high-priority corridor. The section from East Union Street to East John Street just reopened in February with new concrete pavement.

City leaders more recently announced 50 blocks of new sidewalks and safety updates on Rainier Avenue South as part of the Move Seattle package.

Additionally, Metro has paid the city an average of $235,000 annually in recent years for “spot improvements,” or updates on certain roads or routes, according to the SDOT spokesman. Those projects can include replacing torn asphalt with concrete panels at bus stops and along popular routes.

And here’s something: A 2014 study for the American Public Transportation Association says that, due to a lack of bus-weight data, it’s actually unclear to what extent the loads are tied to road damage.

But there’s no question busy Seattle streets are more prone to damage than others.

According to SDOT’s online map of pothole projects, downtown and Capitol Hill seem to get the most work. In February alone, crews repaired more than 3,700 potholes across the city, the agency says.

 

Q: Is it OK to use park-and-ride lots for non-transit carpooling, specifically during weekends when they are not crowded? And if we are heading out on a weekend backpack, what is the maximum time we can stay parked in one of the lots?

— Louise Suhr, Seattle

A: Metro Transit’s 130 park-and-ride lots, totaling more than 25,000 parking spaces, are intended to reduce congestion by getting people into buses, van pools or carpools. Nowadays the question is whether or not you’ll find a spot.

For a weekend trip, though, check to make sure your King County park-and-ride destination is open. Some lots are open only on weekdays.

According to Metro’s policies, vehicles can remain parked in a spot for a maximum of 72 consecutive hours — no matter if it’s the weekend or not.

Patrols by Metro staff enforce that rule, among others. The guidelines are posted at lots’ entrances.

When staff identify vehicles violating lot rules, they may issue a warning or request a tow at the owner’s expense and treat the offenses as civil infractions of up to $500.

According to Metro spokesman Jeff Switzer, King County’s park-and-ride rules are generally consistent with lots owned by other county agencies. The guidelines vary, though, for lots with different owners.

 

Got a question?

Missed last week’s Q&A? We asked our own questions, spotlighting the massive transportation crisis in Atlanta after a fire caused an overpass on Interstate 85 to collapse on March 30.

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