BOSTON (CBS) – Out-of-state drivers who don’t have E-ZPass transponders owe the Commonwealth about $15 million in unpaid tolls on the Massachusetts Turnpike.

MassDOT admits some of that won’t ever be collected.

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Since the cashless pay-by-plate system started in October 2016, Massachusetts has charged out-of-state drivers about $70 million. But, more than 20 percent of that – $15 million – has not been paid.

Electronic tolls on the Massachusetts Turnpike. (WBZ-TV)

Massachusetts has agreements with New Hampshire and Maine to keep drivers there from renewing their registrations if they have outstanding tolls here. But that doesn’t apply to the other 47 states.

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“Prior to implementing All Electronic Tolling on I-90 (the Massachusetts Turnpike), MassDOT estimated that approximately 4 to 5% of total tolling revenue would go uncollected,” MassDOT spokesman Patrick Marvin said in a statement.

He added that was all incorporated into planning their operations, maintenance and capital programs.

Marvin also said MassDOT is still “on track with revenue projections” and they will continue to pursue all unpaid tolls.

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“These outstanding charges from out-of-state customers do not necessarily equate to lost revenue, as MassDOT has several measures in place to collect these funds,” he said, including “contacting customers several times via U.S. mail to ensure they are aware of their outstanding charges” and “consistent review of billing details to ensure correct customer contact information.”