Some Suffolk drivers will get a new bill in the mail soon. Anyone who has used the Downtown or Midtown tunnels since Feb. 1 without an E-ZPass transponder in the car will get an idea of just how expensive a habit that can be when bills from Elizabeth River Tunnels Customer Service Center show up this month.

The company is the private partner with the state in the Public Private Partnership that allows ERT to collect tolls for 58 years in return for building a new Midtown Tunnel tube, renovating and maintaining the existing Midtown and Downtown tubes and building an extension to the Martin Luther King Jr. Expressway.

Especially considering the same trips were free to commuters until Feb. 1, the tolls are not cheap. For passenger vehicles, off-peak tolls are 75 cents each way, and so-called peak travel times, which account for a whopping nine hours of each day, cost an extra quarter. Those prices will take a big jump when the tunnel project is complete, and the agreement with the commonwealth allows ERT to assure itself significant profits each year through ever-increasing toll rates.

But the most expensive thing about the tolls is the fact that drivers without E-ZPass transponders are automatically billed at substantially higher rates than those with transponders.

Drivers who have registered their license plates with the system and who maintain prepaid accounts can use the tunnels without transponders, but they face an extra 75-cent “processing fee” per crossing. For those who neither use a transponder nor register for the prepaid service, the costs are even higher, shooting up to a total of $2.25 for off-peak travel and $2.50 for peak travel, including a $1.50 “processing fee.”

Both of those sets of drivers — whom traffic counts show accounted for 28 percent of all weekdays trips in February — could be in for a shock this month, when the first bills arrive from ERT.

In an effort to convert more Hampton Roads drivers to the E-ZPass system, the company is offering a one-time deal to those drivers who have not yet picked up transponders: Pay your bill within 30 days of the invoice date and then convert to E-ZPass or prove that you already have done so, and the company will waive half the processing fee for your February trips. Your costs will still be higher than if you’d already had a transponder in your car, but you’ll at least save a little money.

To take advantage of the offer, call 855-ERT-ROAD or visit the Elizabeth River Tunnels Customer Service Center at 700 Port Centre Parkway, Portsmouth. Elizabeth River Tunnels customer service representatives are also temporarily located at the E-ZPass Customer Service Centers at 1701 Church St., Norfolk, and 4010 Victory Blvd., Portsmouth. Transponders also are available at the Suffolk Visitor Center and city treasurer’s offices.