More background information would be helpful:

What's the visitor center for?  A national park, a town, etc?  

Is it off a main highway in an isolated area (lots of restroom use) or nestled in a downtown area?

Will it be open throughout the year? Are you trying to calculate AADTs or peak-hour volumes?

 

A few visitors' centers that I've visited were not that busy:

San Luis Reservoir; summer: maybe 5 cars (I drive by this one probably 6 times a year, and have never seen it with a full parking lot.  Perhaps the location is awkward, since it's only about 10 miles from the nearest Santa Nella truckstop.)
Mammoth Lakes; winter: maybe 15 cars
Manzanar; winter: maybe 20 cars
Owens Valley; winter: maybe 5 cars

Could have been the time of year.  However, I think that most
people tend to use their smartphones for most of their informational needs, leaving pitstop as the primary rationale for stopping.  

It seems to me that location probably drives the traffic, more than anything else.  Is it on the way to something that has really high traffic?  Does this ITE cover normal rest stop locations? or even truck stops?  

Used to be that car mileage was low, and cars would have to stop at truck stops and the like, but with the raft of high mileage cars on the roads, there seems to be less of a need to stop, and people will tend to push on toward their destinations.  Going from SF to LA on I-5 is about a 430 mile trip, which used to require at least one stop for gas.  Now, there are cars that can just about make it on a full tank.  I can go from LA to Gilroy on a single tank, so other than food and pitstop and leg stretching, there's not much need to stop in the middle.

TTFN
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