In the latter half of the 19th century, New England was knitted together by networks of railroads extending north, south, and west from Boston, built by private companies operating from eight facilities on the city’s edges. By 1900, these were consolidated into two grand terminals a mile apart. The need for further unification, via a rail tunnel between the two, was recognized almost immediately; but plans faltered during World War I, and the passenger rail industry itself nearly collapsed in the following decades as transportation policy embraced cars and highway expansion. The rail link’s proposed route became a notorious elevated highway. Now the pendulum is swinging back toward rail.

Our cities and regional highway system are collapsing under the weight of ever-increasing congestion. Millennials are embracing transit-oriented living while the economic, environmental, and social justice benefits of good public transportation are being increasingly understood. Good regional transportation not only protects air quality and fosters economic development but also is the single largest factor in a family’s ability to escape poverty and find affordable housing.

The recent challenges of our rail system notwithstanding, we should recognize that in its nearly 400 route miles and 138 stations, we have inherited the core of what could become a world-class regional rail network and at a far lower cost than would be required to create this anew — if that were even possible. System unification is the essential intervention that will unlock this potential. Why?

First, none of our fragmented rail lines provides effective distribution across Boston nor connects fully with existing transit lines, squandering the potential of both. Second, stub-end terminals are highly inefficient, needing vast rail yards on valuable urban land to park the necessary trains, limiting capacity and incurring operating cost penalties of up to $100 million per year. Finally, the disconnection of our northern and southern lines denies everyone north of Boston direct access to the Northeast Corridor, where 30 percent of US jobs are located.

By contrast, a unified system, connected to transit lines, will streamline rail operations while improving service, increasing ridership, unlocking hundreds of acres of urban land for higher uses, improving access to Boston, and creating opportunities for work and housing. You shouldn’t have to uproot the family if your job moves across our de facto Mason-Dixon Line.

Rail unification will benefit Boston, sparing it the waves of traffic it can otherwise expect while spurring investment in our older industrial cities that were built around rail and faltered with its decline. The current real estate bubbles in Boston and Cambridge are a measure of our broken regional transportation system, which rewards the few places that are easily accessible and punishes the rest. This pattern is unjust and unsustainable.

Cities around the world — Zurich, London, Berlin, Hong Kong, and Los Angeles, to name just a few — have built rail tunnels at reasonable cost and minimal disruption using the latest tunnel-boring machine technology, transforming “commuter rail” into the equivalent of urban transit at regional scale and forging a backbone for regional prosperity. This should be a key goal for Boston’s 400th anniversary in 2030.