The tunnel was completed within the federal Interstate program, and was the last major step of it. 90% of the funds were from the federal government. Even then (adjusting for inflation it was a 538 million dollar project. The reason all that extra tax money we got recently cant be used? Well you can look at TABOR for that. Because the new incomes far surpass inflation, the government cant actually use it without voter approval and must refund it to tax payers. We had to pass a new ballot measure just to spend the pot tax and it is limited to health and law enforcement. ( BALLOT BB - 2015)

It doesn't matter how much new tax money we get, the gov is hamstrung to not be able to allocate it, thus they must act within the amount + inflation increases, which isn't much. We have had around 1 million new residents come to the state in the past 10 years, but the government hasn't been able to allocate the funds to infrastructure due to partisan politics and limits placed on it by TABOR.