And, unusually, a de-restricted 70mph through there, iirc.
Toll booths were considered for it at design stage, but there was nowhere acceptable to place them, as there would need to be 12 of them (6 for each direction, and all at one end) to cope with the traffic volume. Two problems: the acreage they would have taken up in a N.T. area, and the impossibility of putting them at the north end, because of the downward gradient approaching, hazardous for HGVs. So, out-of-character for the times, tolls were written out. There was some suggestion at the time that the large number of government ministers using the tunnel, and much of the A3, had something to do with the generous speed limits (all the way to Hook-Chessington), and the lack of toll. Something not easy to get to the Bottomley of.