This aerial view shows the road layout 44 years ago in 1970. The photograph is dated 3 May 1970 (11.40am) and a short distance from the main road vehicles can be seen queuing at the two pay booths.
On the day when this photograph was taken, traffic was not a problem, but this system was subsequently altered, although I don't have dates for the change.
In those days there was a short stretch of dual carriageway by the entrance which afforded a small amount of protection to right turning traffic arriving from the M4 and Windsor, but it was not nearly effective enough at preventing long tailbacks on busy days.

Here is the RWWS Legoland page where this photograph originally appeared