“Feasting on Asphalt” (8 p.m. today, Food Network) takes viewers on a cross-country tour of America’s small roads and quirky eateries. Host Alton Brown and his crew saddle up their motorcycles in South Carolina and plan to ride to Los Angeles. Their only hard and fast plans are to avoid interstates whenever possible and never eat in chain restaurants.

Brown begins “Asphalt” on a gracious note by introducing his cameramen and crew and praising them as equal partners in his gastronomic adventure. They proceed to zigzag from Charleston, S.C., to the Great Smoky Mountains in North Carolina in the course of the first hour. Along the way, they find a hot-dog stand serving a rare orange soda and a 1938 diner that has preserved its architectural integrity at the expense of its culinary soul. Brown interviews a second-generation biscuit chef, discusses soul food and endures tropical thunderstorms with good nature. “Asphalt” will continue over four Saturday nights.

¢ Sharks have been around for hundreds of millions of years, snacking on everything in their path. Discovery Channel’s Shark Week has been around since 1988, taking a big bite out of TV ratings with its weeklong showcase of documentary programming about the killers of the deep. Shark Week begins with an episode of “Dirty Jobs” (8 p.m. Sunday, Discovery) in which host Mike Rowe submits to the indignities and danger of swimming with sharks, tagging them for migratory observation and taking a few shark nips for the sake of science. A shark-themed “Dirty Jobs” returns Friday night, when Mike dons a suit of modern chain mail that he is told renders him completely shark proof. Shark documentaries air nightly through Friday.

¢ But sharks don’t have the dog days of summer to themselves. National Geographic rises to the occasion with six straight nights of new and repeat episodes of “The Dog Whisperer” (8 p.m. Sunday, National Geographic). The beauty of this show, hosted by Cesar Millan, is that they are all exactly alike yet each different in its own addictive fashion. In each half-hour helping, Millan contends with three dog problems, and he manages to calm the canines and train their human owners in short order.

So, which cable marathon will triumph? Will viewers stay cool for school and swim with the sharks, or follow the pack leader and hail Cesar? And can either critter show top Animal Planet’s new soap opera? Will next August bring competition from a “Meerkat Manor” marathon? Cable competition has become a virtual zoo.

Today’s highlights

¢ Scheduled on “Dateline” (7 p.m., NBC): Did the sordid relationship between a woman and her therapist lead to murder?

¢ Sandra Bullock and Nicole Kidman star in the 1998 comedy “Practical Magic” (7 p.m., ABC).

¢ Mark Wahlberg, Charlize Theron, Mos Def and Edward Norton star in the 2003 heist thriller “The Italian Job” (8 p.m., NBC).

Sunday’s highlights

¢ Scheduled on “Dateline” (6 p.m., NBC): A doctor’s dark side is revealed after he is arrested for his wife’s murder.

¢ The Boston Red Sox team up to help a boy in need on “Extreme Makeover: Home Edition” (7 p.m., ABC).