When funding for the Purple Line appeared in President Obama’s budget in March, the light-rail project connecting Montgomery and Prince George’s counties began to take on an air of inevitability. To be sure, critical steps and uncertainty remain, but Maryland transit officials are planning to break ground on the 16-mile line next year. “When,” not “if,” has become the appropriate question.

The Purple Line can deliver many social and economic benefits. But the checkered history of light-rail projects around the nation tells us that these will not fully materialize unless we actively plan for them. Concerns about employment, housing, construction disruptions and the like will fall through the cracks. The promise of this project could disintegrate into myriad problems.

We need to start this planning now. It would be irresponsible to delay this work until we have a certified, gold-plated guarantee that the Purple Line will be built. Intensive community involvement at this stage can only help.

To begin this process, the University of Maryland’s National Center for Smart Growth Research and Education, which I lead, has launched the Purple Line Corridor Coalition. Drawing on models used successfully in Minneapolis-St. Paul and Denver, this initiative is designed to make sure the rail line delivers meaningful economic and social benefits to individuals, businesses and communities all along the route. The effort brings key stakeholders to the table to develop specific goals, measures of progress and coordinated action among dozens of government agencies, businesses and social and community groups.

Moving dirt and pouring concrete cannot be allowed to take precedence over preparing for the broad social impact of such a prominent addition to the region’s infrastructure. The Purple Line represents a bold new direction in transportation for the D.C. region. We have multiple heavy-rail lines that have served the area well. But the Purple Line will be the first light-rail line. It will travel primarily at grade and connect more gracefully with the homes and businesses along the route, as well as with bikes, Zipcars, buses and other sustainable forms of transportation. It will be the first line to connect spokes of the Metro system and to be tailored to the significant number of people seeking to travel from suburb to suburb. Their destinations are not in the District.

We stand on the cusp of a once-in-a-lifetime opportunity to transform south suburban Maryland into a more prosperous and equitable area of the region. To prepare, the state has launched workforce training initiatives to help local residents fill the anticipated construction jobs. But that is just a start; more must be done quickly.

For example, economic incentives should be offered immediately so that employers choose locations accessible to the line. Heavy public investment in projects such as the Purple Line attracts housing development as well. It also tends to increase housing sales and property values in the corridor long before the first train pulls into the first station.

These economic effects are precisely what will create the opportunities to build walkable, mixed-use and vibrant communities between the New Carrollton, College Park, Silver Spring, Takoma and Bethesda Metro stations. But, at the same time, they can displace and disrupt — especially the immigrant and minority communities that dot the Purple Line’s corridor. To protect these communities, efforts must begin to construct affordable housing and preserve cultural resources.

Finally, though construction activity creates jobs, it also causes disruption for existing businesses along the corridor. It affects small, locally owned businesses disproportionately. Efforts must start to help these businesses prepare for success in a higher-rent, higher-traffic environment. Also, it’s not too soon to help launch new small businesses in the corridor.

We began this undertaking recently with the Purple Line Corridor Coalition’s first workshop. Participants from more than 100 public and private organizations came together, along with light-rail veterans from around the country, to forge an organization that will help communities withstand the disruptions of a new service and ultimately thrive alongside it.

Opportunities for transformative development such as the Purple Line are too rare to miss and to important to leave to chance. We must plan to get it right.

The writer, an urban economist and planner, directs the University of Maryland National Center for Smart Growth Research and Education.