I suppose you could read it that way - that they will be paying twice as much as those with tags. But the wording isn't clear, certainly not in the title of the article.

Say a toll was $5 with a tag. Right now, the non-tag toll would be $7.50. After the change, it would go to $10 - a 33.33% increase. Not twice as much.

I think that math is the way to look at it, except I reach the opposite conclusion. The headline is "Drivers will soon pay twice as much to use ZipCash on North Texas toll roads." In your example, everyone pays the $5 toll, but to use ZipCash you pay an additional $2.5 now and will pay $5 soon. The total cost isn't increasing by 100%, but the cost to use ZipCash is. The base tolls are increasing by about a penny per mile (about 5.5%) at the same time, which is a part of the regular increase every two years, but that doesn't figure into the increase amount, because what's doubling isn't the actual cost, but is the premium charged for not using a tag. The increase in the premium will be slightly more than 100% because of the base rate increase but the premium increase is still exactly 100%. The wording could be more precise, and all of this detailed information is publicly available, but a press release isn't the place to put legalese fine print. The cost to use ZipCash, which is in addition to the cost of the toll, is doubling.