While less than half of large U.S. employers offering on-site health facilities plan to add new centers, the majority expect to broaden the on-site health services they currently offer, a new survey shows.

Towers Watson & Co.'s 2015 Employer-Sponsored Health Care Centers Survey, released Thursday, found that 38% of large U.S. employers with on-site health facilities plan to add new centers in the next two years.

But 66% of the employers polled expect to expand the services they currently offer to include services beyond primary care by 2018, according to a summary of survey results.

Benefits professionals from 137 U.S. employers were surveyed from February to March of this year. Of that number, 105 companies representing 4.6 million employees currently offer employer-sponsored health centers, Towers Watson said in a statement.

Many employers believe their health care centers will play a greater role in managing and coordinating employee wellness, according to the survey. Currently, 86% of on-site health care centers offer wellness programs, and 63% provide lifestyle coaching to promote and reinforce behavior changes.

Additionally, half of the centers offer pharmacy services, up from 38% in 2012. One-third of health centers offer telemedicine services, and 12% more plan to add it in the next two years, survey results show.

Of employers that already offer or plan to implement on-site or near-site health centers, 75% do so to increase productivity, 74% to reduce health care costs, and 66% to improve convenient employee access to health services, survey results show.

The vast majority of the centers offer immunizations, draw blood, and care for acute conditions such as upper respiratory and urinary tract infections, the survey said.

Because of the need to control costs, the majority of employers with on-site health centers are now calculating their return on investment. Seventy-five percent calculate the ROI, an increase from 47% in 2012. Of those, 12% of employers use an independent third party to measure results, 33% use their health services vendors, and 30% use internal staff analysis, according to the survey.

“For employers with a critical mass of employees in one or more locations, on-site and near-site health centers can be an integral component of a high-performance health care program,” Bruce Hochstadt, senior consultant at Towers Watson, said in the statement. “Encouraged by their experience to date, many employers with these centers believe providing convenient access to health services increases employee productivity by reducing time away from work. What's more, many are ready to increase their investment.”