Houston ? Witheringly hot temperatures and an electricity shortage forced power utilities around Texas to conduct rolling blackouts for several hours Monday.

As temperatures climbed into the upper 90s – and even to triple digits – thousands of Texans found themselves without power as energy companies heeded an emergency call from the Electric Reliability Council of Texas, which runs the state’s electricity grid. Police rushed to intersections to direct traffic during the afternoon rush hour.

As much as 15 percent of the state’s power supply was already off-line for seasonal maintenance to brace for the summer’s energy usage peaks. Then four power-generating plants shut down unexpectedly amid the stifling heat, said ERCOT spokesman Paul Wattles.

By Monday evening, with the help of the rolling blackouts, ERCOT said operations were back to normal.

Typical usage for Texas in April is about 40,000 megawatts a day, but the state peaked at 52,000 megawatts on Monday, Wattles said.

A recorded high of 101 degrees at Dallas-Fort Worth International Airport broke the previous high of 94, set in 1913 and matched in 1925, according to the weather service. Temperatures reached 107 degrees in Laredo.

ERCOT said the rolling blackouts were needed because the power grid had to decrease its load by 1,000 megawatts on Monday.

A megawatt is enough electricity to power about 210 homes for a year.

“The good news is, (the blackouts) worked,” Wattles said. “This prevents region-wide outages. It isolates the outages so a few people share the pain to avoid a region blackout like we had in the Northeast in 2003.”

The rollouts were limited to the ERCOT grid, which provides electricity to about 80 percent of Texas.

Traffic backed up at intersections in Grand Prairie, just west of Dallas, and in Tyler in eastern Texas during the afternoon rush hour.

ERCOT urged customers across the state to curtail their electricity use.

The weather service said Texas should begin to see more normal temperatures in the 70s by midweek.