Dutch to English Law/Patents Law (general) Road Building Contract

Hi,

I'm translating a contract between a state department and a contractor for the construction of a road. There is a separate reader guide (leeswijzer) to the contract that states that this version of the contract is not suitable for toll roads, irrespective of whether these are "echte tolheffing of schaduwtol".

There is no further context at all.

I've established the former is the standard type of toll road where the user pays the operator direct, in the latter case the toll road operator charges the authorities.

If needs be, I can get around things by rephrasing but I'm curious to know whether anyone has an established translation for " schaduwtol".

TIA
Debs