In the Loop

A CTA trains passes through the Tower 18 junction near the Clark/Lake station in Chicago. (Heather Charles, Chicago Tribune / July 18, 2012)

The CTA is operating special trains that spray water on the tracks and increasing visual inspections during the extreme heat spell to prevent “sun kinks’’ from warping the rails and possibly causing derailments, transit officials said Wednesday.

Temporary slow zones are also in effect over older track, across areas where heavy braking or acceleration is needed and on segments with drainage problems, CTA spokeswoman Molly Sullivan said.

On the Dan Ryan branch of the Red Line, train speeds were recently reduced to 35 mph from the normal 55 mph “to prevent rail spreading,’’ Sullivan said.

The issue was raised at Wednesday’s CTA board meeting when director Ashish Senasked why a performance report showed the CTA was not meeting its target for controlling rail delays. The response from CTA staff was that the heat has stressed the fleet.

CTA as well as Metra trains have suffered heat-related mechanical problems this summer.

Many of the mechanical problems are related to the air-conditioning systems on the rail cars due to constant use, Sullivan said.

"It means we swap out the cars where the A/C has gone out and this usually means limited delays and/or limited car crowding until the replacement cars are in place," she said.

CTA rail crews are carrying out extra safety measures to reduce the risk of sun kinks when temperatures exceed 95 degrees for three days or more with no rain, officials said.

The precautions include additional track inspections in the afternoon to look for rails improperly seated on rail plates that keep the rails secure; loose or lifting rail fasteners and spikes; visible movement of rail ties; and misalignment, kinks or buckles in the track.

The water train is also being used to keep the rails cool, officials said.

RedEye reporter Tracy Swartz contributed.

jhilkevitch@tribune.com