Public transit is a key to drive development in cities, which is becoming more important with Millennials spurring urban migration—78% of respondents to a recent poll of Boston Millennials said workplace proximity to public transit is "very important." Which cities are trying to meet that demand? Here's a rundown of five new urban transportation projects in major markets.

Gateway Project

Location: NJ/NYC

Expected Completion: 2025

Cost: $20B

Commuters to NYC have seen their dreams of a new Hudson River rail-tunnel revived with the Gateway project, whose cost will be split between Amtrak, the Feds and the states of NY and NJ. It's crucial that the project gets a move-on as the current tunnels may have to be shut down to repair damage caused by Superstorm Sandy.

H Street and Benning Road Streetcar

Location: DC

Completed: Early 2016

Cost: $48M

DC's H Street and Benning Road Streetcar line has been in the works since the early 2000s and finally opened at the beginning of 2016. That comes only after several almost-launches, and a couple of streetcar-on-streetcar collisions, of course.

Brooklyn-Queens Connector

Location: Brooklyn

Expected Completion: 2024

Cost: $2.5B

This 16-mile streetcar connecting the two NYC boroughs would be Mayor de Blasio's most ambitious engineering project so far. Just proposed this year, the project wouldn't break ground until 2019. The connector would cut travel time between Queens and BK nearly in half, linking two of the East Coast's hottest markets.

Chicago’s Loop Link BRT

Location: Chicago

Completed: 2015

Cost: $32M

Chicago's Loop Link BRT (Bus Rapid Transit) gives separate lanes and boarding islands to buses in an effort to give buses the same streamlined speed as rail service—without the cost of building tunnels. The success of the project, which started service in late 2015, will determine whether the Windy City moves forward with an expanded version of the project—which could end up being a model for cities across the country.

Second Avenue Subway

Location: NYC

Expected Completion: First phase in late 2016

Cost: $4.45B

Phase 1 of NYC's 2nd Avenue subway line is scheduled to open in December 2016—although that could always get pushed back. The railway was first proposed nearly a century ago, and this first phase will create three new stations between 96th and 63rd streets. No doubt New Yorkers hope the next three phases will finish before the 22nd Century—although they are still unfunded.