I have over twenty of experience preparing estimates and forecasts. This includes 10-years in the public sector as a strategic planner and almost 12-years in the carwash industry as a consultant. I can assure you that forecasting is more of an art than a science.
Accurately determining customer attraction rate and store turnover rate (sales volume) for a carwash site has always been an issue of debate and an area of concern for developers.
Experience has shown that an operator can expect to capture between 0.4% and 1.81% or more of the daily highway traffic passing by a site. This is a very broad forecast interval to consider and capture rate is known to vary considerably depending on category of wash, business model, geographic region and other site location factors.
For example, using annual average daily traffic count (AADT) of 25,000, the lower and upper bounds of capture rate would produce annual site yield of;
25,000 x 0.004 x 312 = 31,200
25,000 x 0.0181 x 312 = 141,180
Some people believe developers should base projections on an average rate. For example, AADT of 25,000 and average rate of 0.7% would produce annual site yield of;
25,000 x 0.007 x 312 = 54,600
This may seem like good advice but the capture rate approach is naive meaning that it is not based on cause and effect. Studies have shown that traffic count capture rate is unbiased but it is not a consistent estimator of carwash sales volumes. In other words, there is too much unexplained error in the estimate to content with or bet on.
There are a number of ways beside capture rate to estimate and forecast carwash volumes such as analogue-based procedures, discriminate analysis, analogue-based regression analysis, gravity models, spatial models as well as statistical procedures to merge individual estimates into an indicated volume to improve the degree of confidence.
I have an entire section on my website that provides an overview of customer attraction as well as other stuff like location assessment that you might find of interest in dealing with your problem.
I would provide it the web address, but I don’t believe I am allowed to.
However, if you know how to surf a little bit, I’m sure you will be able to track it down.