GRTC is looking for a new leader.

The search is about to begin following the sudden resignation of David Green, GRTC’s chief executive officer, less than two months after launching the new Pulse bus rapid transit system ushering in a controversial overhaul of all other GRTC bus routes.

Mr. Green, who had led the company since January 2014, notified employees following a special board meeting Wednesday that he would be leaving at the end of August.

It is was not immediately clear whether he made the decision to step down or was forced out by the six-member GRTC board that includes three representatives from Richmond and three from Chesterfield County.

Mr. Green told employees in his email that the time had come for him to seek “a new opportunity and professional growth” after nearly two decades with the company.

Sheryl Adams, GRTC’s chief operating officer, is expected to be named interim CEO during the board’s search for a new chief executive.

In his email to employees, Mr. Green said he had sought to develop a company of which the entire region could be proud by ensuring GRTC offered meaningful service.

He also ticked off 16 innovations he helped usher in since taking over from former CEO Eldridge Coles, who is now a board member. They ranged from funding, developing and starting Pulse to the creation of passes providing unlimited rides, installation of modern fare boxes and development of mobile payment apps.

He also led GRTC’s shift from using air polluting diesel fuel to power buses to cleaner compressed natural gas that now powers 75 percent of the fleet.

During his tenure, GRTC also installed its first Downtown transfer station and inked a $1.2 million deal with Virginia Commonwealth University to provide free rides to students, faculty and staff on the GRTC system in the city.

Mr. Green also completed preparations for a new program to provide free, unlimited rides on GRTC for Richmond Public Schools’ high school students in partnership with the city.

Mr. Green joined GRTC in 1999 as assistant finance director. He later served as director of procurement and grants management and as chief of staff to Mr. Coles before being tapped for the top job.