Mayor Vincent Gray looks toward the original streetcar while making remarks as he welcomes the second in a fleet of three electric trolley cars for H street on May 1, 2013 in Washington, D.C. (Bill O'Leary/The Washington Post)

On a rainy morning this spring, D.C. Mayor Vincent C. Gray led a group across Connecticut Avenue NW to demonstrate an unusual traffic signal designed to protect pedestrians when they want to cross but allow traffic to flow at all other times.

Gray (D) said this was an example of what he wants: a city that accommodates drivers while encouraging other forms of travel, whether on bikes, buses, streetcars or feet.

The day after the ceremonial Connecticut Avenue crossing, the mayor greeted the arrival of the District’s first modern streetcars, destined for the tracks embedded along H Street and Benning Road NE. “I’m just anxious to see them start service,” he said.

The pedestrian signals and the streetcars are the hardware of the mayor’s transportation policy. So are the bollards that mark the bike lanes on L Street NW.

But what’s the policy? Gray administration officials are engaged in a variety of initiatives, including a Parking Action Agenda, designed to shape street use, and moveDC, billed as a collaborative effort to figure out how people will get around the city.

Yet no document explains the long-term vision like the mayor’s Sustainable D.C. program to make the District “the healthiest, greenest, and most livable city in the United States” — all in 20 years.

To understand how the hardware fits together, look at the transportation part of the plan.

Sustainable D.C.

“In the Sustainable D.C. plan we released earlier this year,” the mayor said at the crosswalk event, “we set an aggressive-but-realistic goal of increasing the use of public transit, biking and walking to comprise 75 percent of all commuter trips in the District in the next 20 years.”

In other words, Gray told me afterward, the future of city travel is about sharing routes safely. Look for more bus routes, streetcars, bike lanes and devices such as the pedestrian signal, which can make walking safer and more popular without infringing on people’s ability to drive autos.

But for any city, getting three of four commuter trips done without cars is a major shift in people’s behavior. Why set the target so high?

“We’re looking at adding 250,000 people over 20 years,” Gray said. “If everyone drives, that’s unsustainable.”

Goals and targets

This is the heart of the plan.

Goal 1: To improve connections among communities and make them more accessible by developing efficient, integrated and affordable transit systems.

Target: By 2032, increase use of public transit to 50 percent of all commuter trips.

How: Complete a 37-mile streetcar network. Improve transit connections to employment and activity centers from underserved areas. Secure permanent funding for transit planning and improvements.

Goal 2: Expand safe, secure infrastructure for cyclists and pedestrians.

Target: By 2032, increase biking and walking to 25 percent of all commuter trips.

How: Develop a 100-mile, citywide bicycle-lane network. Expand the Capital Bikeshare program by 200 stations. Team with community organizations on bike- and pedestrian-safety education. Collect data to improve the understanding of cyclist and pedestrian travel patterns. Program crosswalks and traffic lights for improved safety and convenience of pedestrians and cyclists.

Goal 3: Reduce traffic congestion to improve mobility.

Target: By 2032, reduce commuter trips made by car or taxi to 25 percent.

How: Expand the performance-based parking program, in which meter rates vary based on demand. Expand car-sharing programs to low-income residents. Encourage private businesses to offer incentives for employees to travel by public transit, walking or biking. Promote telecommuting and alternative work schedules. Study the feasibility of a regional congestion fee for travel during peak hours.

Goal 4: Improve air quality along major transportation routes.

Target: By 2032, eliminate all air-quality index days designated as “unhealthy,” including the lower category of “unhealthy for sensitive groups.”

How: Strictly limit idling engines. Require the D.C. government to purchase clean-fuel, low-emission fleet vehicles, and encourage private businesses to do the same. Expand electric vehicle charging stations throughout the city. Offer incentives to avoid driving and other emission-generating activities on predicted unhealthy air-quality days.

Is it sustainable?

On Connecticut Avenue, Gray not only demonstrated the crossing, but also instructed passersby on its proper use.

“Did you hear that?” he asked those nearby when the signal’s audio alert was activated.

But Gray won’t be around every time a resident has a question about all this transportation hardware, and there already are plenty of questions. Some drivers and pedestrians wonder how safe the unfamiliar signals are. Others see the streetcar tracks along H Street and wonder how the new-style trolleys will get around ­double-parked cars. Many motorists suspect that the bike lanes are part of a broader effort to squeeze them off the roads.

And that’s just the hardware. It’s unlikely Gray and the rest of today’s policymakers will be around to personally sustain the policies in two decades.

So, what sustains Sustainable D.C.?

It sustains itself, Gray said, because it makes sense. In fact, much of the hardware and many of the policies are common in big U.S. cities today.

There’s even a history in the District on some of this, and it predates Gray’s administration. The first of those innovative pedestrian signals was installed on Georgia Avenue in 2009, with D.C. Council member Muriel Bowser (D-Ward 4) on hand to lead some residents of her ward across. (Bowser is a candidate for mayor in the 2014 election.) The streetcar program had symbolic groundbreakings under two mayors, Anthony A. Williams and Adrian M. Fenty.

Nonetheless, Gray is right to call his transportation plan “aggressive.” And some city dwellers — in particular, longtime residents who like getting around by car — are suspicious about his intentions.

I asked the mayor whether he wants to take residents’ cars away.

“We’re not looking to take people’s cars,” he said. “That wouldn’t be democratic — and it wouldn’t work.”

Rather than coercing change, Gray said, he hopes that people will change their travel behavior because the city provides them with the options to change their behavior.

Besides political pushback, there’s reality pushback. If population trends indicate that the city is falling short of its ambitious goal of adding a quarter-million residents in two decades, and if a declining interest in autos fails to become a long-term trend, the goals in Sustainable D.C. won’t seem as urgent or as achievable as they might today.