Vehicle apparatus includes a speed control for adjusting a vehicle powertrain of the vehicle in response to a speed setpoint. A grade estimator determines a road grade of a roadway where the vehicle is traveling. A traffic density estimator determines a density of traffic traveling on the roadway in the vicinity of the vehicle. An optimizer executes a selected control policy to periodically generate speed adjustments for applying to the speed setpoint to operate the vehicle powertrain at increased efficiency. The control policy is based on a value function providing an optimized solution for a cost model responsive to the determined road grade to generate an initial speed offset. The optimizer reduces the initial speed offset in proportion to the determined traffic density to generate the speed adjustments. The system minimizes negative impacts to overall traffic flow as well as any negative contribution to reduced fuel efficiency of surrounding traffic.