Fans of the sport say to truly appreciate NASCAR racing, you have to attend an event in person to see the cars whizzing by, hear and feel dozens of vehicles revving to over 9,000 rpm as they throttle up to the green flag at the start of the race, and smell the burnt rubber from a spinout or a tire-smoking victory celebration. The 91,000-plus fans sitting in the stands at last month's Nextel Cup race at New Hampshire International Speedway attest to the sensory experience of big-time auto racing.

But the on-site crowd probably didn't know that on lap 21 Kasey Kahne got his red No. 9 car up to 157 mph on the front stretch before slowing down to a more leisurely 96 mph to take the curve. Or that Ricky Rudd's 21 car was traveling at precisely 67 mph when it hit the wall rear-end first on lap 211. Viewers at home had all this information and more courtesy of the on-screen graphics that were part of the TNT live coverage of the Siemens 300 race.

Calculating and displaying real-time information such as speed takes more than a well-aimed radar gun and some quick hands on a keyboard. "It's the most complicated graphic to produce in television," says Bob Hess, track engineer for Sportvision, the Chicago technology company NASCAR contracts with to produce the real-time data and associated graphics for the television broadcasts.

In the TV compound that sat just outside the grandstand behind Turn 3 at the New Hampshire course, Hess and his team of a half-dozen engineers sat in one of the 13 TV trucks on site to produce the race. Sportvision's truck is dedicated to receiving, compiling and distributing telemetry and position data from each car in the race and pushing it out to regular TV, pay-per-view, the Web and Nextel cellular phones.

Each car is equipped with a GPS receiver embedded in the roof and a Data Acquisition and Positioning System (DAPS) black box mounted near the rear window that collects braking, throttle position and rpm information. Using a 900-MHz transmitter, the DAPS and GPS information is radioed to one of the three or four base stations positioned around the track. Multiple base stations are used for redundancy purposes, as objects in and around the track could block the signal. The telemetry data and GPS data is collected five times per second. To get from the base station to the truck, Sportvision taps into fiber cable connecting the camera positions around the track or a DSL modem connected to Category 3 cabling.

Cat 3? "It's cheaper [than Cat 5] and it works," says Ken Milnes, senior vice president of engineering at Sportvision.

Inside the truck, the communications controller (known as CC) aggregates all the data, including the official timing information from NASCAR, which is provided via an RS-232 serial interface. "CC organizes the data in a way that's useful for the other applications we run," Milnes says, adding that a proprietary format is used to store the data.

A Cisco Catalyst switch connects Windows XP and Linux machines used to produce graphics. Coaxial cable feeds the graphics data to the other production trucks for the TV broadcast. A machine called T-Sync helps synchronize the time codes from the video feed with the GPS time data.