There are 623 million cars and trucks on roads worldwide--enough for one vehicle for every nine people on the planet. If that's not enough room for growth, one-fourth of the vehicles in operation are more than 12 years old and closing in on the end of their life cycles, concludes a new study on the vehicles in use worldwide by Ward's Communications and U.K.-based Pemberton Associates. Even more surprisingly, 110 million of the oldest vehicles in operation can be found in the more-developed countries of the world.

The report, Ward's 1994 Worldwide Vehicle Parc and Age, also reveals that General Motors Corp.-brand cars and trucks are the most prevalent worldwide, with 109 million in operation. Ford Motor Co.-brand vehicles follow at 76