The magic of three does not extend to the “fast” lane of interstate highways — at least not without some dollar signs attached.

John Dewhirst, of Edmonds, wonders if the Washington State Department of Transportation will change I-5 high-occupancy vehicle lane rules to three or more occupants — rather than the current two-plus rule — given persistent congestion in the lanes.

Congestion in the HOV lanes “from Everett to Seattle is seriously hampering the buses maintaining their schedules,” Dewhirst said.

Community Transit commuter buses on I-5 were late one quarter of the time in 2014, and HOV lane drivers had to budget more than 1 hour 10 minutes if they wanted to get to Seattle on time.

With no room to expand the interstate along its length, folks such as Dewhirst say an occupancy hike makes sense.

“I think the time for such a study and determination is long overdue,” Dewhirst said.

A 2011 University of Washington study of the ongoing problem noted another possible solution that takes things a step further: Kick out carpools entirely and make the I-5 HOV lanes transit-only.

But in both cases — going three-plus or transit-only — the writers noted it may not be “politically feasible.”

Nor would it necessarily be wise on its own, say planners with the Washington State Department of Transportation.

Either of those fixes would certainly solve HOV congestion, but at the expense of the general purpose lanes, making bad congestion there even worse.

Keeping the regular lanes moving — even if it’s at a snail’s pace — is still a priority, too, with lots of economy-driving business in the corridor. Not everyone can accommodate a second occupant, much less a third. Think also of the semi-truck driver moving freight, who is banned from the HOV lane regardless.

“We need to be looking at the system as a whole. … They’re all great customers. They move a ton of people,” said Travis Phelps, a WSDOT spokesman. “It’s a balance that we have to keep going.”

For now, encouraging more people to join a van pool or get on a bus might be the best bet for reducing congestion in the HOV lane.

“Transit and van pool vehicles on I-5 at the Snohomish-King County line comprise less than 350 vehicles during peak commute times,” said Justin Fujioka, another WSDOT spokesman. “These wonderful forms of transit offer tons of benefits, but it is difficult to justify an HOV three-plus switch at the present time.”

Light rail could make at least a tiny dent on the problem. If the Sound Transit 3 proposal passes the November ballot, Community Transit buses one day could bow out of the I-5 commute.

Then there’s that magic word: tolling.

If HOV lanes on I-5 do go to a three-plus carpool requirement, it likely would be in conjunction with tolling — the same approach the state took on I-405.

When is 45 mph required?

So at what point do things get bad enough that change is forced?

There is no legal mandate that the state increase the occupancy requirement — or do much of anything, actually — in its HOV lanes.

State policy says to “consider” going three-plus when an HOV facility is no longer reliably moving drivers along at speeds of at least 45 mph.

The federal government only enforces that 45 mph standard (specifically, a minimum 45 mph over 90 percent of the peak commute hours in a 180-day period) if a state allows single occupant drivers to use the lanes — such as by paying a toll.

In the past year, California has had to explain why it’s failed that standard after allowing tens of thousands of hybrid vehicles to use its HOV lanes regardless of occupancy, as well as toll-paying single drivers. More than half of the Bay Area’s HOV lanes are considered degraded.

The feds told the state to increase the occupancy requirement, increase tolls on toll lanes, kick out clean-air vehicles with solo drivers, or build more lanes.

In response, California planners slammed the standard as too stringent — claiming it can be missed with just two crash-plagued weekdays — and claim the real measure of success is whether the reserved lanes move folks faster than the regular lanes.

Maybe it’s not 45 mph, but 35 mph is still better than 20 mph.

The Federal Highway Administration could still hand WSDOT some advice on I-5 if a public outcry reached its offices, said Nancy Singer, a spokeswoman in Washington D.C.

But there’s limits to what transportation planners can do, she noted.

“If it’s congestion — what do you do?” Singer said. “It’s an overall congestion management question or solution, and it’s not easy.”

Meanwhile, the state will start reporting to the feds its reliability rates on the I-405 express toll lanes after hitting the one-year mark in late September.

So far, the state says it’s meeting the 45 mph standard — barely.

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