You may need to Google that article title and click through to read it but it outlines that even at $7 each way the price wasn't high enough so now it's $10 each way (not $8 as I stated.) Even so, the $3 price hike has done little to ease congestion.
Clearly the only scientific thing would be to have different tolls on different weekdays. Monday: $25, Tuesday: $10, Wednesday: $17, Thursday: $50, Friday: $31. Now you can see which price eases congestion the most!