About six weeks after the debut of dynamic toll lanes in I-66, motorists are still seeing occasional eye-popping spikes in tolls.

Drivers this past week reported tolls above $40 at certain points, approaching record highs set shortly after the toll system opened in December.

The new toll system is designed to encourage carpooling and public transit, and keep traffic moving along I-66 eastbound. Tolls change every 6 minutes and rise and fall based on traffic conditions. The tolls are only in effect from 5:30 a.m. to 9:30 a.m. eastbound and 3 p.m. to 7 p.m. westbound.

Wednesday was a particularly high-traffic day, as some motorists may have been forced onto I-66 by the closure of Clara Barton Parkway. Tolls hit as high as $46.75 that morning, or 25 cents below a record high.

It did not help that on at least one occasion earlier this month, the app and website to check real-time tolls was not working. This prevented some drivers from knowing toll charges before they hopped on the highway.

Drivers can avoid paying a toll if they have at least one passenger and have a special E-ZPASS transponder for carpoolers.