The vote will decide whether the 10 Greater Manchester authorities will accept a £3bn package of Transport Innovation Fund (TIF) money for transport improvements, with a peak time congestion charge in 2013, or not.
Seven of the 10 authorites must vote for the TIF package for the plans to be carried.
Polls suggest that the vote is too close to call, with a margin of error indicating the result could go either way.
Voter turnout is predicted to be high - possibly on par with the last general election - which would favour a "yes" vote. More than 1M votes are understood to have been counted so far, bringing the total proportion to more than 50%.
To maximise the number of votes counted, post offices throughout Manchester were "sweeped" last night to ensure every vote cast would count.