The solution to the rush-hour bottleneck along the three lanes in each direction of the H-1 freeway in Makiki seems temptingly simple: Grab the paint brush and turn the freeway into four lanes each way. That may seem to be the logical solution, but it also may come with increased danger of vehicles coming too close to each other.

The recommended national standard for the width of traffic lanes is 12 feet, but numerous freeways across the country have gone through an "exception process" to achieve a more slender dimension. The lanes of the H-1 between Punahou and Middle streets are 11.5 feet wide. The state Department of Transportation is considering a proposal to reduce that width to 10 feet and all but eliminate the shoulders, now measured from 3 to 4 feet wide near the center divider and 4 to 6 feet wide on the outside lanes, according to department spokesman Dan Meisenzahl.

The consequences may be severe. The Federal Highway Administration put it bluntly: "On high-speed roadways with narrow lanes that also have narrow shoulders, the risk of severe lane-departure crashes increases." Meisenzahl said the change may require reducing the present 50 mph speed limit by 5 mph.

That may not be enough.

Today’s compact sedans measure about 5.5 feet wide, but they may be dwarfed by tour buses and semitrailer trucks, which federal law allows to measure up to 8 feet, 6 inches wide, not including mirrors or footholds that may extend the width close to the edges of 10-foot lanes.

What will happen when a next-generation tiny electric or hybrid car becomes overwhelmed by a bus and big-rig truck? There’s also the question of how today’s jumbo-sized SUVs will fare, jammed into narrow lanes next to big trucks or buses. The result may be an unreasonable trade-off between freeway capacity and safety.

Although no specific study on narrowing freeway lanes has been conducted in recent decades, the Washington-based Advocates for Highway and Auto Safety has long frowned on such a change, noting there is a tendency for the driver of a car to shy away from the truck by squeezing closer to the other lane.

"The narrowing of the lanes is a problem for safety, because for people who weave in and out of lanes or who move to avoid a can in the road or a piece of tire, there’s no leeway within the lanes to get around it," said Henry Jasny, the organization’s vice president.

The virtual elimination of shoulders also is not good, he said, "because you have no breakdown lane. When people have an (engine) overheat or have an emergency and they have to pull out of the highway, that’s what shoulders are used for."

The addition of an extra lane each way on H-1 is appealing for commuters who struggle daily to drive to and from work, and state transportation officials get points for broaching for discussion creative options to combat bottlenecks. But officials need to examine the consequences of similar changes in other urban areas. The proposal may seem too good to be safe.