The problem of controlling the congestion front in a single link road section is considered in this paper. For this purpose, we introduce a new variable-length two-cell lumped model composed of; one congested cell, and another in free flow. This model has the advantage of having few states while preserving the vehicle conservation property. This model is used as a basis to design a simple "best-effort" controller that regulates (at its best) the congestion front to some prespecified value. The control law can be implemented using only information about the congestion front position.