As many of you know, General Motors is planning to equip all 1995 models with daytime running lights (DRL's). The rationale for public consumption is the company's concern for highway safety. The less skeptical might take this at face value. The more suspicious will look for dollar signs behind the motivation.
No one argues that daytime running lights will increase fuel consumption (something has to power those lights), or that additional maintenance expenditures will be generated through the replacement of bulbs and related components. In the long run, this means more income for GM, although not a great deal. Conversely, DRL's will make it just that more difficult to stay on the right side of federal Corporate Average Fuel Economy Standards.
There is considerable debate over whether DRL's have a significant or lasting effect on highway safety. While Canada and Scandinavia mandate DRL's, Italy specifically prohibits their use. Our own NHTSA remains ambivalent on the value of DRL's.
The issue may not be as cut and dry as might first be thought. Under many circumstances, DRL's should improve visibility. Under other circumstances, they may be a source of irritation and a causative factor in certain kinds of accidents. (Lights can distort estimates of distances between approaching vehicles.) This may be a simple tradeoff of one kind of accident for another, more serious type of accident.
A good example of confounding effects is "right turn on red." Legalizing right turns on red lights increased right turn accidents at controlled intersections. However, it reduced other types of intersection accidents at a rate far in excess of that for accidents caused. Conversely, the installation of stop signs, cross walks, and traffic lights quite frequently increases the number, if not the severity accidents occurring at a given location. The tradeoff is traffic control.
If GM senses that DRL's hurt sales in 1995, it may be a one year experiment, or they may go after Congress to make DRL's mandatory, so that all manufacturers will be at an equal disadvantage. We can only sit back and watch the story unfold.