What is the current state of the law in the context of cross-examination of a defendant in a motor vehicle case?

In Barshfield v. Vucklich (1921), 108 Kan. 761, 197 P. 205, the court stated: 'Another objection is that the court permitted inquiry as to other acts of careless driving and of accidents resulting from it. This testimony was drawn out in the cross-examination of the defendant. He had testified that he was a careful driver and was driving carefully at the time of the accident. He was then asked if he had not been stopped and reprimanded by officers for fast driving, if he had not run into a light pole, if he had not struck a boy, and had not been arrested for careless driving. To some of these inquiries he gave an affirmative answer and to others he entered a denial. On the direct examination no evidence was offered as to his driving habits or of careless driving on other occasions. The general rule is that acts of negligence on other occasions than the one in question are, with a few exceptions, inadmissible. [210 Cal.App.2d 422] [Citation.] Here, however, it was only a cross-examination of the defendant himself as to his claim of careful driving, and no reason is seen why such an inquiry may not be permitted within reasonable limitations.' (197 P. at pp. 206-207.)

In People v. Downs (1952), 114 Cal.App.2d 758, 762, 251 P.2d 369, 371, the court held that the defendant had 'opened the door to any competent evidence calculated to disprove his sweeping assertion of reform.'