This year's heat-shortened, chaotic Chicago marathon prompted organizers of Wellstone's Dallas White Rock Marathon to make a number of safety-related changes to prepare for Sunday's race.

"(Dallas) police called me the next day to talk about what happened in Chicago and to ask how we were going to be prepared," said Marcus Grunewald, race director for the White Rock marathon.

Record temperatures and high humidity at the 30th annual Chicago marathon on Oct. 7 caused runners to wilt along the 26.2-mile course. Officials closed the race after 49 people were taken to the hospital and another 250 were treated at the scene.

Some 3 ½ hours into the race, officials decided to cancel it. About 10,000 of the 45,000 registered runners never showed up; nearly 11,000 started the race but didn't finish.

"This forced us to think of something we never thought of before, namely, a mass evacuation," Mr. Grunewald said. "I don't know what would cause us to have a mass evacuation, but neither did Chicago, so we need to be prepared."

In his six-year tenure as race director, Mr. Grunewald said, he has not encountered any major emergencies – just the usual handful of runners who get tired and need a ride to the finish line or the threat of bad weather.

Dallas runners will begin at 8 a.m. at American Airlines Center, wrap around White Rock Lake and return to Victory Park. A 13-mile course opens at 9 a.m. for half-marathon competitors. Some 15,000 people are expected to participate in the full and half marathon and the marathon relay.

Mr. Grunewald noted that if officials had to close the course, runners could be 13 miles from the starting line.

"We will have buses on standby," Mr. Grunewald said. "We have an emergency plan on how to get the runners back to the finish line in case of an emergency. In Chicago, the runners had to walk back, and we don't want that to happen."

Many runners in the Chicago race complained that the heat was made worse by a lack of water. Wendy Hazelwood, 32, of Dallas said the water stations were about two to 2 ½ miles apart.

"That's inadequate," she said. "The humidity was so high you could not keep enough water in. You were thirsty about a half-mile after you left the water stop."

Marcus Grunewald

In Dallas, race organizers use water faucets and fire hydrants along the course to ensure that water will be plentiful, Mr. Grunewald said. The White Rock course has water stations every mile for the last two-thirds of the race.

This year, as a precaution, Mr. Grunewald had ordered small blowtorches to put at the aid stations to warm the faucets if they freeze. But the forecast of warmer-than-normal temperatures for race day has prompted him to take steps to ensure there will be extra ice and cups along the route.

Ms. Hazelwood, who also coaches marathon training for Luke's Locker, said she had two-tenths of a mile to go when the Chicago race was called, so she ignored the bullhorns telling her to stop running and finished the race in just under four hours. She already had abandoned her goal of crossing the finish line in 3:40.

"It wasn't a normal race," she said. "I knew it was going to be a bad day for everybody at mile 13 when you would see people in fast pace groups – guys trying to qualify for Boston – walking on the side of the road cramping and hurling. That's not common."

Heat usually isn't as much of a concern for White Rock marathon organizers. Instead they worry that extreme cold could keep away the hundreds of volunteers who work the water stations, Mr. Grunewald said.

To improve communications, Dallas police have tweaked their plans by adding a mobile command post with a ham radio operator and a phone list for ambulances stationed on the course, Sr. Cpl. Jimmy Bailey said.

In previous years, police communicated through radios, but the new system will provide a contact person in a central location.

"This race has always been smooth and well-organized," Cpl. Bailey said. "We just brushed the dust off."

Mr. Grunewald said other changes include the banning of audio devices, such as iPods, although that rule was put into place by USA Track and Field, the governing body for running. Spreading the word that the race was closed in Chicago was difficult because runners were listening to music and couldn't hear the bullhorns, he said.

The Dallas race will include at least 10 message boards along the course that could help instruct runners in case of an emergency, Mr. Grunewald said.

"Like Chicago, it's easy to get complacent with the emergency plan," Mr. Grunewald said. "It was a good wakeup call to remind us that every year you have to think fresh about what could happen."

What: The 38th running for Wellstone's Dallas White Rock Marathon

When: Sunday, 8 a.m.

Start and finish: American Airlines Center

Registration: Sold out

Estimated number of runners: 15,000

TV: Ch. 8

Wellstone's Dallas White Rock Marathon, 8 a.m. Sunday, Victory Park, Dallas (Ch. 8)