Currently, tolls allocate in one-dimension only, the physical realm: they have an impact on which road a person takes. The tolls on the turnpike cause some drivers to avoid the pike for local roads. The quite reasonable fear that toll hikes will cause an increase in cut-through, toll-avoiding traffic is quite reasonable. It is likewise reasonable to expect that reducing or eliminating tolls would reduce cut-through traffic.
But, there is a downside to reducing or eliminating tolls. You make it more attractive. Restricted resources that are free or priced too low are poorly used. The turnpike is a restricted resource, there is limited capacity. Giving that capacity away mis-allocates the resource. Imagine two drivers, one willing to pay a reasonable toll and one not. Removing the toll creates congestion that the first driver would have been willing to pay to avoid. Of course, imposing a toll, if it is the same price round-the-clock, causes that driver to use other roads, causing congestion there.
Not all toll avoiders are going to use other roads. Some will decide not to take the trip. Others will take mass transit. But still, there is an enormous impact on local roads.
The situation would be much different if we added another dimension to tolls: time. Imagine if the gas-tax gang proposed to reduce or eliminate tolls off-peak. Now our toll avoider has another choice: travel at a different time. Everybody wins. The willing toll payer faces less congestion as toll avoiders are given another option. The toll avoider who has the flexibility to travel off peak gets the benefit of the turnpike (compared to stop-and-go local roads). Local road users see a reduction in traffic from the toll avoiders that time-shift their travel. The tolls continue to operate as an incentive to use transit. And, the state maintains the revenue stream during peak travel.
There are going to be an awful lot of MetroWest commuters who are not going to be pleased once they live through the congestion that is the entirely foreseeable — even if unintended — consequence of removing the tolls.