Whether you're a driver or a cyclist, the section of West River Parkway lying below the old St. Mary's Hospital is arguably the worst parkway segment in the city.

Southbound drivers have been known to shift into the oncoming lane to avoid the plethora of potholes. The surface has been patched so many times that the jolting can leave a cyclist feeling scatter-brained.

But help is on the way. Starting April 29, the parkway will close for five weeks between S. 4th Street and Franklin Avenue for renovation.

Crews will mill the badly deteriorated parkway a full seven inches deep, and then replace the road surface. Preliminary wore to replace some curbing and concrete crosswalks and adjust manhole heights is already causing some lane closures for parkway users.

'They'll love it when it's done," said Mike Kennedy, the city's street maintenance supervisor.

The work is part of a long-term program of parkway paving done for the Park Board by the city's Department of Public Works. The budget is $500,000 annually, and it's intended to provide a 20-year fix.. In some cases, maintenance workers need mill down only the top two inches of asphalt. But in this case, they're going down a full seven inches, which may take them into virgin soil.

That's based on what Kennedy said that crews have found in other parkway locations. The parkways, built in the 1970s, were supposed to have seven inches of paving over a gravel base. But often that's not what crews are finding, according to Kennedy. Good road building practice lays paving atop a thick base of gravel so that roadway subsurfaces can drain. That keeps the freeze-thaw cycle from heaving pavement. It's particulrly surprising that that such a base is absent given that some sections of parkways run on unstable peaty soils near lakes or swamps.

Curious, we contacted Jeff Spartz, a park commissioner for part of the '70s, and an advocate for preventive maintenance. "That is a surprise to me," Spartz said, when informed of Kennedy's findings. "That explains why that thing is so bad."

Spartz recently drove the section slated for repairs. "It was a frightmare," he said. "No one was going over the speed limit, I can assure you of that." He noted that the payoff from preventive maintenance is often 20-30 years down the road, too long a horizon to be a priority for many politicians.

In case you're among those who wondered why the sections north and south of the one scheduled for this year's work were done last year while this far worse section was left untouched, there's a logic explained by Park Commissioner Scott Vreeland. Metro storm tunnel work where S. 4th meets the parkway meant heavy equipment was using the adjacent parkway into the fall, so it didn't make sense to risk that new paving would get damaged, he said.