The city of Seattle announced plans Wednesday to crack down on speeding and motorists driving illegally through crosswalks after one pedestrian was killed and two others injured within 24 hours.

Tatsuo Nakata, the chief of staff to City Councilman David Della, was struck Tuesday morning and later died. Wednesday morning, an 11-year-old boy and a 57-year-old woman were struck in separate incidents.

The city will install a mobile radar station near the West Seattle intersection where Nakata, 29, was struck, Mayor Greg Nickels' office said Wednesday. The city also will install signs in the area to remind drivers to watch for pedestrians.

"Drivers especially must take responsibility for keeping our streets safe," Nickels said in a news release. "When you are behind the wheel, a thoughtless moment can take a life. I'm calling on all drivers to slow down, follow the rules and stay aware."

Seattle police said the radar station will be installed today.

Nakata was walking in a marked crosswalk at 47th Avenue Southwest and Southwest Admiral Way at 7:41 a.m., when he was struck by a station wagon, according to Seattle police. He was taken to Harborview Medical Center, where he died later Tuesday.

The 35-year-old driver, whose name was not released, was questioned and released, Seattle police said.

Wednesday morning, a 57-year-old woman was struck by a car while she crossed at First Avenue South and South Lander Street, near Safeco Field, at 6:43 a.m. She was hospitalized with serious injuries, police said.

Not even an hour later, an 11-year-old boy suffered minor injuries after he was struck near California Avenue Southwest and Southwest Hinds Street, in West Seattle. The collision happened shortly after 7:30 a.m. outside Madison Middle School, a district spokeswoman said.

Police are investigating all three crashes.

So far this year, Seattle police have given out 596 citations to motorists who did not yield to pedestrians. There were 461 given in 2005 and 183 in 2003, according to the mayor's office.

This year, police have given 1,964 citations to pedestrians for jaywalking. There were 1,811 given out in 2005 and 1,107 given out in 2004.

Jennifer Sullivan: 206-464-8294 or jensullivan@seattletimes.com