Adding HOV lanes along Interstate 45 to ease traffic between Spring and Conroe is becoming the little project that can’t open.

After first anticipating a June opening on the long-awaited project, Texas Department of Transportation officials said crews are still working on the finishing touches and have missed the fourth revised deadline in as many months. The latest estimate had the southbound lanes opening by the end of September and the northbound lanes from FM 1960 to Loop 336 ready by mid-October.

“Work just isn’t progressing at the rate they predicted,” TxDOT spokeswoman Deidrea George said. “So southbound will definitely not open by the end of the month.”

Delays have been common on the 18-mile HOV lane addition. In mid-2014, officials said they hoped to begin construction in about a year and finish by the end of the 2015. Citing funding challenges, TxDOT didn’t start construction until October, with a plan to open the lanes in April.

Slow-going and weather-related stops in work meant the April completion was pushed to June. By summer, George said misplaced and incorrectly labeled overhead signs pushed the opening to August. Rains in August kept crews from painting the lane markings, and since then workers have failed to achieve their expected pace of painting two miles per day.

Drivers have anxiously awaited the opening.

The project, estimated to cost $2.6 million, is meant as relief for area carpoolers. More than 240,000 vehicles per day use I-45 near the Harris County line, and development and jobs continue to increase in the area around The Woodlands and Conroe.