For this year's AJC Peachtree Road Race, there's something old, something new, and, well, something old that's new again. Here's a look at some milestones for this year's July 4 run.

• Old: AJC Peachtree Road Race hits the big 4-0.

AJC Peachtree Road Race organizers now call it the world's largest 10K, but it began in 1970 with 110 people who thought light holiday traffic might make for a nice run down the city's premier street. Back then, they started at the corner of Peachtree and Ros-well roads, then headed down to Central City Park, which is now Woodruff Park.

These days, the route is different, the size has gradually ballooned to 55,000 runners and nearly half of them are women. For its 40th run, the race and its commemorative T-shirts are firmly rooted in Atlanta's July 4 traditions.

But how?

"There's always been a capacity issue, always been a greater demand than the ability to accommodate," says Tracey Russell, the Atlanta Track Club's executive director.

"When you create an event that dates back that far, there just continues to be that buzz. If you get in, you're one of the lucky ones."

What has stayed the same since the beginning? Ten kilometers, and, of course, AJC Peachtree Road Race T-shirts for runners.

• New: Electronic timing for all

Nobody was timed electronically during that first run — "there was no such thing," Russell says. And through last year, only seeded runners and those in "Time Group One" received an electronic timing device.

This year, for the first time, though, all 55,000 runners will receive a disposable tag that tracks when they cross the start and finish lines. The tags, made by Indiana-based company ChronoTrack, will be sent to runners with their race numbers and directions on how to attach them on race day. Volunteers will be on hand July 4 to help racers with them, too. More information about the tags is available at www.atlantatrackclub.org.

• Old and New: Peachtree returns to Piedmont Park

Since 1978, the Peachtree had ended along the edges of Piedmont Park. That changed last year when drought forced the race to end at the intersection of Juniper Street and Ponce de Leon Avenue.

Runners heaved a collective sigh of relief when it was announced earlier this year that the race will end back at 10th Street at Charles Allen Drive, where runners and their supporters can trickle on to the Meadow in Piedmont Park.

"The course evolved over the years, but the connection has always been to Piedmont Park," Russell said. "It was a relief to be able to finish where this event has such a strong identity."