Willy tragically concludes that he is 'worth more dead than alive', having scrimped to keep up with insurance payments. His suicide illustrates the sad fact that he can still only equate worth with money and popularity: not the love of family.
As stated above, Willie commits suicide in a final effort to achieve some semblance of success. The money from the life insurance policy is unlikely to be paid out however because the policy does not cover death by suicide.
In the play Willie is concerned that he has been a complete failure, which is true in some ways. He has not managed to achieve a great deal of professional success. However, he and his wife have paid off their house - an achievement which he ignores - and they have raised two healthy, relatively capable children. Willie does not recognize these feats as achievements, comparing his life to the quick and astonishing financial success of his brother.
Suicide is Willie's final failure and also his final attempt at success, again demonstrating his miscomprehension of value.
Willy kills himself by crashing his car. He does in order to allow his son Biff to cash in on his insurance policy, allowing him to begin his own business, which was Willy's ambition for him. Biff, however, never wanted to be a businessman, and it is actually Willy's other son Happy who used the money as Willy had hoped.