Four ways people express their anger when driving were identified. Verbal Aggressive Expression (alpha=0.88) assesses verbally aggressive expression of anger (e.g., yelling or cursing at another driver); Personal Physical Aggressive Expression (alpha=0.81), the ways the person uses him/herself to express anger (e.g., trying to get out and tell off or have a physical fight with another driver); Use of the Vehicle to Express Anger (alpha=0.86), the ways the person uses his/her vehicle to express anger (e.g., flashing lights at or cutting another driver off in anger); and Adaptive/Constructive Expression (alpha=0.90), the ways the person copes positively with anger (e.g., focuses on safe driving or tries to relax). Aggressive forms can be summed into Total Aggressive Expression Index (alpha=0.90). Aggressive forms of expression correlated positively with each other (rs=0.39-0.48), but were uncorrelated or correlated negatively with adaptive/constructive expression (rs=-0.02 to -0.22). Aggressive forms of anger expression correlated positively with driving-related anger, aggression, and risky behavior; adaptive/constructive expression tended to correlate negatively with these variables. Differences in the strengths of correlations and regression analyses supported discriminant and incremental validity and suggested forms of anger expression contributed differentially to understanding driving-related behaviors. Theoretical and treatment implications were explored.