Referendum in Leiden: referendum placards

This Wednesday the people of Leiden can vote whether they want a regional railway through their city. The railway is called "RGL", which stands for Rijn Gouwe Lijn (or: Rhine-Gouwe Line).
At election time these boards are put up so that the parties can advertise (for free) their parties or, in this case, their pro or contra stance on the RGL.
Even if the people of Leiden vote against the RGL, it is doubtful it can be stopped, because it is a regional project and the regional government can overrule the Leiden city council.