About a year before the Food, Drug and Cosmetic Act was amended to include menu labeling, researchers associated with Yale and led by Christina Roberto conducted several studies to explore the effects of menu labeling on purchasing behavior. They were able to use NYC for some of these tests because NYC had added mandatory menu labeling in 2008.  Other scientists have also reviewed these policies.
   As the details of the national law were being negotiated, restaurant owners suggested that drive through menu boards be exempt from the calorie disclosures.  Instead they suggested that a notice be placed on the boards that informed customers about nutrient information that was available in side or on line.  There were problems with this idea.  First, studies had already shown that customers rarely noticed information or made use of it if it was not directly at the point of sale.  Because of this, it was likely that some proportion of fast food customers would not benefit from the law if it exempted drive through order boards.
   Roberto, et al observed customer traffic at 8 different fast food establishments during specific time periods for a total of 39 separate observations. (in Connecticut)  They categorized over 3500 customers as either inside or drive through orderers.  The results of their study likely impacted the final menu labeling rule.  In total, across all the restaurants,  57% of the customers used the drive through.  Curiously,  the lowest drive through rate was at Kentucky Fried Chicken (36%) and the highest was at Dairy Queen (70%) followed by Taco Bell (63%).  
   You might think, well, those were CT restaurants.  This is true, but it is likely that similar numbers would be found in other states.  The researchers' conclusion that menu labeling is needed on the drive through boards as well as inside makes good sense to me.  
   At last check, the legislation does include the drive through boards.  I am hoping to find some time this week to review the status of the vending and menu laws.  The FDA (through the secretary of Health and Human Services) is responsible for explaining to restaurant and vending owners exactly what they have to do, when they have to do it, what the penalty will be for not doing it, and when the FDA will begin enforcement.   The last I read, all is delayed, but the final rule may come out this fall.

The study that I referenced is available here.
Roberto CA, Hoffnagle E, Bragg MA, Brownell KD.
Public Health Nutr. 2010 Nov;13(11):1826-8. Epub 2010 Mar 18.