New York City Department of Transportation

New York City, it should be noted, has a speed limit: 30 miles per hour unless otherwise noted. The Transportation Department is hoping a pixelated image of a skeleton won’t let you forget it.

A custom-designed speed board — those radar-equipped digital signs that tell drivers how fast they are moving — will be unveiled this summer that sends a spooky message to lead-footed New Yorkers: a gaunt LED skeleton appears whenever it detects a car exceeding the 30 m.p.h. limit on city streets.

To underscore the deadly consequences of speeding, the skeleton is a bony version of the familiar pedestrian stick-figure who appears on crosswalk lights.

Skeletons are already a trope of the Transportation Department’s “That’s Why It’s 30” advertising campaign, which reminds drivers through bus shelter ads and television spots that cars traveling at 40 m.p.h. are far more dangerous to pedestrians than vehicles that follow the speed limit. The Transportation Department has not yet determined where the boards will be placed.

Mayor Michael R. Bloomberg, at a news conference on Thursday, compared the signs to cigarette packs sold in other countries that include a skull-and-crossbones label to warn about lung cancer. “Unless you make it graphic, people don’t get the message,” the mayor said.

The city is also planning to introduce a slower, 20 m.p.h. speed limit in certain residential areas as part of a pilot program that starts this summer in the Claremont section of the Bronx.

Of course, in the most congested parts of Manhattan below Central Park, automobiles rarely reach anywhere near the speed limit: on an average weekday, cars crawl along at an anemic 9.3 miles per hour.

But Janette Sadik-Khan, whose tenure as transportation commissioner has coincided with a drop in traffic deaths to their lowest point in a century, said that the city needed a way to grab drivers’ attention. The mayor concurred.

“If you save one life, it’s one of the more brilliant ideas I’ve ever heard,” Mr. Bloomberg said. “Who knows whether it’s going to save a life? But at least we’re trying to save lives rather than just sitting around and complaining and saying people should.”

Another of Ms. Sadik-Khan’s signature initiatives, bicycle lanes, appear to be enjoying an increasingly positive response from New Yorkers, even if many wonder whether they get much use, according to a citywide poll released on Thursday.

More than half of the survey respondents said they considered bicycle lanes a way to make the city “greener and healthier,” compared with 39 percent who leaned toward the view that the lanes impede automobile traffic.

But only a quarter of those polled said they believed the lanes were widely used by cyclists. About 44 percent said they believed that the lanes were rarely used and 29 percent said they were not sure.

The poll was quickly seized upon by bicycle advocates as evidence that the lanes enjoyed “landslide approval,” in the words of a press release from Transportation Alternatives. The survey takers themselves, however, offered a more nuanced assessment.

“We sort of like bike lanes, but few of us see any sign that they’re heavily used,” said Maurice Carroll, director of the Quinnipiac University Polling Institute, in summarizing New Yorkers’ views.

Mr. Bloomberg, asked on Thursday about the survey, said he believed the frigid winter weather had skewed New Yorkers’ perspective of the lanes’ popularity.

“I keep hearing people tell me that ‘oh, no people are using them,’ ” the mayor said. “Well, keep in mind, the weather is better. In the middle of the winter, fewer people bicycle, so when the weather gets better, you would expect that. But there is a lot of evidence that people want bicycles.”

The lanes received support from a majority of respondents in nearly every borough and demographic group, although registered Republicans remained opposed. Older New Yorkers are also less likely to support the lanes than voters under the age of 50.

The polling institute surveyed 962 registered voters; the poll had a margin of sampling error of plus or minus 3 percentage points.