The emergency shutdown of Light Street for the past three weeks to replace a broken water main should be a teachable transportation moment for Baltimore.

There is now significantly less traffic on Light Street in the heart of downtown and its northward St. Paul Street extension, giving greatly desired relief to the Mount Vernon neighborhood.

After some inevitable initial confusion, the traffic has found other routes and adapted well, demonstrating that motorists are adaptable and traditional travel routes can be changed.

So even as they reopen Light Street next week, transportation officials and center city booster groups should pause and learn from the Light Street closure to achieve their avowed goal of creating a more “livable downtown.”

Despite years of tinkering, the street environment of downtown traffic is pretty much as bad as ever. The traffic on St. Paul through Mount Vernon and Preston Gardens moves too fast due to the city’s traffic signal timing.

The ten-lane section of Light Street downstream in the Inner Harbor remains as vast and formidable a traffic obstacle as ever.

Dispersion and the “Embarcadero Effect”

The key to the closure impact was the “catchment area” of the Light Street traffic. The extent to which Light Street attracts longer trips from larger distances determines the ability of the traffic to disperse to other routes.

Since Light is a southerly extension of St. Paul and Charles Street all the way north to the Beltway, the traffic has many route options covering a very wide area.

The city knows this capability very well from the occasional construction disruptions on the nearby parallel Jones Falls Expressway (JFX), for which traffic has been affected all the way eastward to Belair Road. Light and St. Paul Street carry much of the same traffic.

The JFX off-ramp dumps a huge volume onto St. Paul through Mount Vernon, and in fact, this traffic has not been greatly reduced by the Light Street closure, since these motorists have now become able to whip down St. Paul faster than ever amid the reduced competition for street space.

Less traffic has moved over to the adjacent parallel southbound routes on Maryland and Guilford Avenues than one might expect. More affected has been the traffic feeding into St. Paul and then Light Street from the northeast Harford/Belair corridor via Hillen and Pleasant Streets into Preston Gardens.

The greatest volume of this traffic has diverted to Holliday, then Saratoga to Guilford Avenue behind City Hall. This route has become more congested, but still viable.

Planners and anti-traffic activists like to cite the “Embarcadero Effect” to explain this.

They like to point out that when San Francisco’s elevated Embarcadero Freeway was damaged by an earthquake and then torn down 20 years ago, the dire congestion predicted on surrounding streets did not materialize.

Instead, much of the traffic just seemed to disappear. But the key was that the Embarcadero served traffic from a huge area, including well beyond San Francisco itself, all the way from the Golden Gate Bridge to the Richmond-San Rafael Bridge to Oakland.

Traffic does not disappear. It disperses. The full effects, including secondary “domino” diversions, are too complex to be explained by even the most detailed travel simulation models.

Light Street’s catchment area is not quite as big as the former Embarcadero. But just a glimpse at Baltimore’s geography, especially its relationship to the harbor, shows that its downtown streets are situated to attract far more traffic concentration than they should.

So the big questions are:

Where, if anywhere, should the traffic be dispersed to?

And what city goals should be pursued?

There are numerous present and future city projects that respond to downtown traffic flexibility.

First is the brand new bikeway route along Guilford Avenue and Fallsway, which occupies a lane in the Jones Falls “prison district.” This route could be readily used by north-south traffic from the Mount Vernon corridor, including St. Paul/Light Street corridor, although in the opposite return direction.

And consider the Baltimore Grand Prix, for which traffic barricades have already been erected a month in advance. Virtually the entire Inner Harbor will be closed to normal car traffic over the Labor Days weekend in favor of 175-mph race cars.

Both the bike and race car projects take advantage of the inherent traffic flexibility to push traffic away.

Peering into the future, the most publicized proposal is the $1-billion demolition of the lower JFX to create a greenway between Mount Vernon and the prison district.

The most publicized goal is to transform downtown into an actual neighborhood, converting old, outmoded office buildings to residential use and transforming commercial streets into residential streets.

Downtown Partnership has proposed major projects endorsed by the city to change traffic patterns on each end of the current Light Street closure.

Just north of the closure, they have proposed a major reworking of Preston Gardens. South of the closure, they want to realign and narrow Light Street so that the northbound segment in the Inner Harbor no longer flows into Calvert Street, but instead flows as a two-way street into the Pratt intersection and presumably for several more blocks to include the portion which is currently closed.

Creating a Consistent Vision

The experience of the Light Street closure strongly indicates that the traffic impacts of both projects are eminently manageable, and that there is potential to do far more.

Instead of narrowing Light Street to eight lanes in the Inner Harbor, much of it can probably be narrowed to six or even four lanes.

The city’s proposed roundabout at the southern end of the Inner Harbor at Light and Key Highway appears to be gross traffic overkill compared with what is warranted. For Preston Gardens, far greater traffic mitigation should be possible to create a true continuous greenway from the downtown end at Lexington Street northward to the Mount Vernon end at Centre Street.

If the city got serious about traffic relief for Mount Vernon, it could be transformed to resemble Bolton Hill or Otterbein.

However, narrowing and realigning Light Street in the Inner Harbor to lessen its impact is in direct conflict to accommodating the Grand Prix. Reducing traffic and transforming the Mount Vernon streets into a residential environment is in direct conflict to the idea of tearing down the JFX and dispersing its traffic.

And while one might think that accommodating bikes and creating a neighborhood environment would go hand in hand, locating the new bikeway on the Fallsway indicates otherwise.

Fallsway, Guilford Avenue and the JFX are direct dispersal routes for Mount Vernon traffic. And the streets’ physical design and traffic engineering need to be consistent with their role and function.

In sum, there are serious conflicts between short- and long-range city goals and projects, which range from the Grand Prix frenzy to overall livability. The emergency closure of Light Street demonstrates the potential to turn Baltimore into the city we want.

But that will happen only if we are attuned to the way people and traffic patterns are able to respond.

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Gerald Neily was transportation planner for the Baltimore City Department of Planning from 1977 to 1996.